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In [[compiler]] design, '''static single assignment form''' (often abbreviated as '''SSA form''' or simply '''SSA''') is a property of an [[intermediate representation]] (IR), which says that each variable is assigned exactly once. Existing variables in the original IR are split into ''versions'', new variables typically indicated by the original name with a subscript in textbooks, so that every definition gets its own version. In SSA form, [[use-define chain|use-def chains]] are explicit and each contains a single element.
 
SSA was developed by [[Ron Cytron]], [[Jeanne Ferrante]], [[Barry Rosen (computer scientist)|Barry K. Rosen]], [[Mark N. Wegman]], and [[F. Kenneth Zadeck]], researchers at [[International Business Machines|IBM]] in the 1980s.
 
In [[functional language]] compilers, such as those for [[Scheme (programming language)|Scheme]], [[ML programming language|ML]] and [[Haskell (programming language)|Haskell]], [[continuation-passing style]] (CPS) is generally used while one might expect to find SSA in a compiler for [[Fortran]] or [[C (programming language)|C]].  SSA is formally equivalent to a well-behaved subset of CPS (excluding non-local control flow, which does not occur when CPS is used as intermediate representation), so optimizations and transformations formulated in terms of one immediately apply to the other.
 
==Benefits==
The primary usefulness of SSA comes from how it simultaneously simplifies and improves the results of a variety of [[compiler optimization]]s, by simplifying the properties of variables. For example, consider this piece of code:
 
  y := 1
  y := 2
  x := y
 
Humans can see that the first assignment is not necessary, and that the value of <code>y</code> being used in the third line comes from the second assignment of <code>y</code>. A program would have to perform [[reaching definition|reaching definition analysis]] to determine this. But if the program is in SSA form, both of these are immediate:
 
  y<sub>1</sub> := 1
  y<sub>2</sub> := 2
  x<sub>1</sub> := y<sub>2</sub>
 
[[Compiler optimization]] algorithms which are either enabled or strongly enhanced by the use of SSA include:
*[[constant propagation]]
*[http://llvm.org/devmtg/2007-05/05-Lewycky-Predsimplify.pdf value range propagation]
*[[sparse conditional constant propagation]]
*[[dead code elimination]]
*[[global value numbering]]
*[[partial redundancy elimination]]
*[[strength reduction]]
*[[register allocation]]
 
==Converting to SSA==
Converting ordinary code into SSA form is primarily a simple matter of replacing the target of each assignment with a new variable, and replacing each use of a variable with the "version" of the variable [[reaching definition|reaching]] that point. For example, consider the following [[control flow graph]]:
 
<center>
[[Image:SSA example1.1.png|An example control flow graph, before conversion to SSA]]
</center>
 
Notice that we could change the name on the left side of "x <math>\leftarrow</math> x - 3", and change the following uses of <var>x</var> to use that new name, and the program would still do the same thing. We exploit this in SSA by creating two new variables, <var>x</var><sub>1</sub> and <var>x</var><sub>2</sub>, each of which is assigned only once. We likewise give distinguishing subscripts to all the other variables, and we get this:
 
<center>
[[Image:SSA example1.2.png|An example control flow graph, partially converted to SSA]]
</center>
 
We've figured out which definition each use is referring to, except for one thing: the uses of <var>y</var> in the bottom block could be referring to ''either'' <var>y</var><sub>1</sub> or <var>y</var><sub>2</sub>, depending on which way the control flow came from. So how do we know which one to use?
 
The answer is that we add a special statement, called a ''Φ (Phi) function'', to the beginning of the last block. This statement will generate a new definition of <var>y</var>, <var>y</var><sub>3</sub>, by "choosing" either <var>y</var><sub>1</sub> or <var>y</var><sub>2</sub>, depending on which arrow control arrived from:
 
<center>
[[Image:SSA example1.3.png|An example control flow graph, fully converted to SSA]]
</center>
 
Now, the uses of <var>y</var> in the last block can simply use <var>y</var><sub>3</sub>, and they'll obtain the correct value either way. You might ask at this point, do we need to add a Φ function for <var>x</var> too? The answer is no; only one version of <var>x</var>, namely <var>x</var><sub>2</sub> is reaching this place, so there's no problem.
 
A more general question along the same lines is, given an arbitrary control flow graph, how can I tell where to insert Φ functions, and for what variables? This is a difficult question, but one that has an efficient solution that can be computed using a concept called ''dominance frontiers''.
 
Note: the Φ functions are not actually implemented; instead, they're just markers for the compiler to place the value of all the variables, which are grouped together by the Φ function, in the same location in memory (or same register).
 
According to Kenny Zadeck<ref>Zadeck, F. Kenneth, [http://citi2.rice.edu/WS07/KennethZadeck.pdf ''Presentation on the History of SSA''] at the [http://www.prog.uni-saarland.de/ssasem/ SSA'09 Seminar], Autrans, France, April 2009</ref> Φ functions were originally known as ''phoney'' functions while SSA was being developed at IBM Research in the 1980s. The formal name of Φ function was only adopted when the work was first published in an academic paper.
 
===Computing minimal SSA using dominance frontiers===
First, we need the concept of a [[dominator (graph theory)|''dominator'']]: we say that a node A ''strictly dominates'' a different node B in the control flow graph if it's impossible to reach B without passing through A first. This is useful, because if we ever reach B we know that any code in A has run. We say that A ''dominates'' B (B is ''dominated by'' A) if either A strictly dominates B or A = B.
 
Now we can define the [[dominator (graph theory)|''dominance frontier'']]: a node B is in the dominance frontier of a node A if A does ''not'' strictly dominate B, but does dominate some immediate predecessor of B (possibly node A is an immediate predecessor of B. Then, because any node dominates itself and node A dominates itself, node B is in the dominance frontier of node A.). From A's point of view, these are the nodes at which other control paths, which don't go through A, make their earliest appearance.
<!-- Need an example -->
 
Dominance frontiers capture the precise places at which we need Φ functions: if the node A defines a certain variable, then that definition and that definition alone (or redefinitions) will reach every node A dominates. Only when we leave these nodes and enter the dominance frontier must we account for other flows bringing in other definitions of the same variable. Moreover, no other Φ functions are needed in the control flow graph to deal with A's definitions, and we can do with no less.
<!-- Describe the algorithm for finding dominance frontiers in the future -->
 
One algorithm for computing the dominance frontier set<ref name="Cooper_2001">{{cite paper
|title=A Simple, Fast Dominance Algorithm
|last=Cooper |first=Keith D. |coauthors=Harvey, Timothy J.; and Kennedy, Ken |year=2001 |url=http://www.cs.rice.edu/~keith/EMBED/dom.pdf }}</ref> is:
 
'''for each''' node b
    '''if''' the number of immediate predecessors of b ≥ 2
        '''for each''' p '''in''' immediate predecessors of b
            runner := p
            '''while''' runner ≠ idom(b)
                add b to runner’s dominance frontier set
                runner := idom(runner)
 
Note: in the code above, an immediate predecessor of node n is any node from which control is transferred to node n, and idom(b) is the node that immediately dominates node b (a singleton set).
 
There is an efficient algorithm for finding dominance frontiers of each node. This algorithm was originally described in Cytron ''et al.'' 1991.<ref name="Cytron_1991">{{cite journal
|title=Efficiently computing static single assignment form and the control dependence graph
|author=Cytron, Ron; Ferrante, Jeanne; Rosen, Barry K.; Wegman, Mark N.; and Zadeck, F. Kenneth |journal=ACM Transactions on Programming Languages and Systems |volume=13 |year=1991 |pages=451&ndash;490 |url=http://www.cs.utexas.edu/~pingali/CS380C/2010/papers/ssaCytron.pdf |issue=4
|doi=10.1145/115372.115320 }}</ref> Also useful is chapter 19 of the book "Modern compiler implementation in Java" by Andrew Appel (Cambridge University Press, 2002). See the paper for more details.
 
Keith D. Cooper, Timothy J. Harvey, and Ken Kennedy of [[Rice University]] describe an algorithm in their paper titled ''A Simple, Fast Dominance Algorithm''.<ref name="Cooper_2001" /> The algorithm uses well-engineered data structures to improve performance.
 
== Variations that reduce the number of Φ functions ==
"Minimal" SSA inserts the minimal number of Φ functions required to ensure that each name is assigned a value exactly once and that each reference (use) of a name in the original program can still refer to a unique name. (The latter requirement is needed to ensure that the compiler can write down a name for each operand in each operation.)
 
However, some of these Φ functions could be ''[[dead code elimination|dead]]''.  For this reason, minimal SSA does not necessarily produce the fewest number of Φ functions that are needed by a specific procedure.  For some types of analysis, these Φ functions are superfluous and can cause the analysis to run less efficiently.
 
===Pruned SSA===
Pruned SSA form is based on a simple observation: Φ functions are only needed for variables that are "live" after the Φ function. (Here, "live" means that the value is used along some path that begins at the Φ function in question.) If a variable is not live, the result of the Φ function cannot be used and the assignment by the Φ function is dead.
 
Construction of pruned SSA form uses [[live variable analysis|live variable information]] in the Φ function insertion phase to decide whether a given Φ function is needed.  If the original variable name isn't live at the Φ function insertion point, the Φ function isn't inserted.
 
Another possibility is to treat pruning as a [[dead code elimination]] problem.  Then, a Φ function is live only if any use in the input program will be rewritten to it, or if it will be used as an argument in another Φ function.  When entering SSA form, each use is rewritten to the nearest definition that dominates it. A Φ function will then be considered live as long as it is the nearest definition that dominates at least one use, or at least one argument of a live Φ.
 
===Semi-pruned SSA===
Semi-pruned SSA form <ref>{{cite paper
|title=Practical Improvements to the Construction and Destruction of Static Single Assignment Form
|year=1998 |last=Briggs |first=Preston |coauthors= Cooper, Keith D.; Harvey, Timothy J.; and Simpson, L. Taylor |url=http://www.cs.rice.edu/~harv/my_papers/ssa.pdf }}</ref> is an attempt to reduce the number of Φ functions without incurring the relatively high cost of computing live variable information.  It is based on the following observation: if a variable is never live upon entry into a basic block, it never needs a Φ function.  During SSA construction, Φ functions for any "block-local" variables are omitted.
 
Computing the set of block-local variables is a simpler and faster procedure than full live variable analysis, making semi-pruned SSA form more efficient to compute than pruned SSA form.  On the other hand, semi-pruned SSA form will contain more Φ functions.
 
==Converting out of SSA form==
SSA form is not normally used for direct execution (although it is possible to interpret SSA<ref>{{cite paper
|title=Interpreting programs in static single assignment form |year=2004 |last=von Ronne |first=Jeffery |coauthors=Ning Wang; Michael Franz |url=http://dl.acm.org/citation.cfm?doid=1059579.1059585 }}</ref>), and it is frequently used "on top of" another IR with which it remains in direct correspondence.  This can be accomplished by "constructing" SSA as a set of functions which map between parts of the existing IR (basic blocks, instructions, operands, ''etc.'') and its SSA counterpart.  When the SSA form is no longer needed, these mapping functions may be discarded, leaving only the now-optimized IR.
 
Performing optimizations on SSA form usually leads to entangled SSA-Webs, meaning there are phi instructions whose operands do not all have the same root operand. In such cases color-out algorithms are used to come out of SSA. Naive algorithms introduce a copy along each predecessor path which caused a source of different root symbol to be put in phi than the destination of phi. There are multiple algorithms for coming out of SSA with fewer copies, most use interference graphs or some approximation of it to do copy coalescing.
 
==Extensions==
Extensions to SSA form can be divided into two categories.
 
''Renaming scheme'' extensions alter the renaming criterion. Recall that SSA form renames each variable when it is assigned a value. Alternative schemes include static single use form (which renames each variable at each statement when it is used) and static single information form (which renames each variable when it is assigned a value, and at the post-dominance frontier).
 
''Feature-specific'' extensions retain the single assignment property for variables, but incorporate new semantics to model additional features. Some feature-specific extensions model high-level programming language features like arrays, objects and aliased pointers. Other feature-specific extensions model low-level architectural features like speculation and predication.
 
==Compilers using SSA form==
SSA form is a relatively recent development in the compiler community.  As such, many older compilers only use SSA form for some part of the compilation or optimization process, but most do not rely on it.  Examples of compilers that rely heavily on SSA form include:
 
*The ETH [[Oberon-2]] compiler was one of the first public projects to incorporate "GSA", a variant of SSA.
 
*The [[LLVM]] Compiler Infrastructure uses SSA form for all scalar register values (everything except memory) in its primary code representation.  SSA form is only eliminated once register allocation occurs, late in the compile process (often at link time).
 
*The [[Open64]] compiler uses SSA form in its global scalar optimizer, though the code is brought into SSA form before and taken out of SSA form afterwards.  Open64 uses extensions to SSA form to represent memory in SSA form as well as scalar values.
 
*As of version 4 (released in April 2005) GCC, the [[GNU Compiler Collection]], makes extensive use of SSA. The [[front and back ends|frontends]] generate "GENERIC" code which is then converted into "[[GIMPLE]]" code by the "gimplifier". High-level optimizations are then applied on the SSA form of "GIMPLE".  The resulting optimized intermediate code is then translated into [[Register Transfer Language|RTL]], on which low-level optimizations are applied. The architecture-specific [[backend]]s finally turn RTL into [[assembly language]].
 
*[[IBM]]'s open source adaptive [[Java virtual machine]], [[Jikes RVM]], uses extended Array SSA, an extension of SSA that allows analysis of scalars, arrays, and object fields in a unified framework. Extended Array SSA analysis is only enabled at the maximum optimization level, which is applied to the most frequently executed portions of code.
 
*In 2002, [http://citeseer.ist.psu.edu/721276.html researchers modified] IBM's JikesRVM (named Jalapeño at the time) to run both standard Java [[byte-code]] and a typesafe SSA ([[SafeTSA]]) byte-code class files, and demonstrated significant performance benefits to using the SSA byte-code.
 
*[[Oracle Corporation|Oracle]]'s [[Java HotSpot Virtual Machine]] uses an SSA-based intermediate language in its JIT compiler.
*[[Mono (software)|Mono]] uses SSA in its JIT compiler called Mini.
*[http://jackcc.sf.net jackcc] is an open-source compiler for the academic instruction set Jackal 3.0.  It uses a simple 3-operand code with SSA for its intermediate representation.  As an interesting variant, it replaces Φ functions with a so-called SAME instruction, which instructs the register allocator to place the two live ranges into the same physical register.
 
*Although not a compiler, the [[Boomerang (decompiler)|Boomerang decompiler]] uses SSA form in its internal representation. SSA is used to simplify expression propagation, identifying parameters and returns, preservation analysis, and more.
 
*[[Portable.NET]] uses SSA in its JIT compiler.
*[http://pp.ipd.kit.edu/firm/ libFirm] a completely graph based SSA intermediate representation for compilers. libFirm uses SSA form for all scalar register values until code generation by use of an SSA-aware register allocator.
 
*The Illinois Concert Compiler circa 1994<ref>{{cite web|url=http://www-csag.ucsd.edu/projects/concert.html|title=Illinois Concert Project}}</ref> used a variant of SSA called SSU (Static Single Use) which renames each variable when it is assigned a value, and in each conditional context in which that variable is used; essentially the static single information form mentioned above.  The SSU form is documented in [http://www-csag.ucsd.edu/papers/jplevyak-thesis.ps John Plevyak's Ph.D Thesis].
 
*The COINS compiler uses SSA form optimizations as explained here: http://www.is.titech.ac.jp/~sassa/coins-www-ssa/english/
 
*The [[Chromium (web browser)|Chromium]] [[V8 JavaScript engine]] implements SSA in its Crankshaft compiler infrastructure as [http://blog.chromium.org/2010/12/new-crankshaft-for-v8.html announced in December 2010]
 
*[[PyPy]] uses a linear SSA representation for traces in its JIT compiler.
 
*[[Android (operating system)|Android]]'s [[Dalvik (software)|Dalvik]] virtual machine uses SSA in its JIT compiler.
 
*The Standard ML compiler [[MLton]] uses SSA in one of its intermediate languages.
 
*[[LuaJIT]] makes heavy use of SSA-based optimizations.<ref>{{cite web|url=http://wiki.luajit.org/Optimizations|title=Bytecode Optimizations|publisher=the LuaJIT project}}</ref>
 
==See also==
*[[Compiler optimization]]
*[[Valgrind]]
*[[Jimple]]
 
==References==
 
===Notes===
{{reflist}}
 
===General references===
* {{cite book |author=Appel, Andrew W.
|title=Modern Compiler Implementation in ML
|publisher=Cambridge University Press |year=1999 |isbn=0-521-58274-1 }} Also available in [[Java (programming language)|Java]] (ISBN 0-521-82060-X 2002) and [[C (programming language)|C]] (ISBN 0-521-60765-5, 1998) versions.
* {{cite book |author=Cooper, Keith D.; and Torczon, Linda
|title=Engineering a Compiler
|publisher=Morgan Kaufmann |year=2003 |isbn=1-55860-698-X }}
* {{cite book |author=Muchnick, Steven S.
|title=Advanced Compiler Design and Implementation
|publisher=Morgan Kaufmann |year=1997 |isbn=1-55860-320-4 }}
* {{cite journal |author=Kelsey, Richard A.
|title=A Correspondence between Continuation Passing Style and Static Single Assignment Form
|journal=ACM SIGPLAN Notices |year=1995 |volume=30 |issue=3 |month=March |pages=13–22 |doi=10.1145/202530.202532 }}
* {{cite journal |author=Appel, Andrew W.
|title=SSA is Functional Programming
|journal=ACM SIGPLAN Notices |year=1998 |volume=33 |issue=4 |month=April |pages=17–20 |doi=10.1145/278283.278285 }}
* {{cite journal |author=Pop, Sebastian
|title=The SSA Representation Framework: Semantics, Analyses and GCC Implementation
|year=2006 |url=http://cri.ensmp.fr/people/pop/papers/2006-12-thesis.pdf }}
* {{citation | author=Matthias Braun, Sebastian Buchwald, Sebastian Hack, Roland Leißa, Christoph Mallon, Andreas Zwinkau| title=Simple and Efficient Construction of Static Single Assignment Form| year=2013| volume=7791| pages=102–122| publisher=Springer Berlin Heidelberg| series=Lecture Notes in Computer Science| doi=10.1007/978-3-642-37051-9_6| url=http://www.cdl.uni-saarland.de/projects/ssaconstr| accessdate=24 March 2013}}
 
==External links==
* Bosscher, Steven; and Novillo, Diego. [http://lwn.net/Articles/84888/ GCC gets a new Optimizer Framework]. An article about GCC's use of SSA and how it improves over older IRs.
*[http://www.dcs.gla.ac.uk/~jsinger/ssa.html The SSA Bibliography]. Extensive catalogue of SSA research papers.
* Zadeck, F. Kenneth. [http://webcast.rice.edu/webcast.php?action=details&event=1346 "The Development of Static Single Assignment Form"], December 2007 talk on the origins of SSA.
 
{{DEFAULTSORT:Static Single Assignment Form}}
[[Category:Compiler construction]]
[[Category:Articles with example pseudocode]]

Revision as of 05:40, 22 March 2013

In compiler design, static single assignment form (often abbreviated as SSA form or simply SSA) is a property of an intermediate representation (IR), which says that each variable is assigned exactly once. Existing variables in the original IR are split into versions, new variables typically indicated by the original name with a subscript in textbooks, so that every definition gets its own version. In SSA form, use-def chains are explicit and each contains a single element.

SSA was developed by Ron Cytron, Jeanne Ferrante, Barry K. Rosen, Mark N. Wegman, and F. Kenneth Zadeck, researchers at IBM in the 1980s.

In functional language compilers, such as those for Scheme, ML and Haskell, continuation-passing style (CPS) is generally used while one might expect to find SSA in a compiler for Fortran or C. SSA is formally equivalent to a well-behaved subset of CPS (excluding non-local control flow, which does not occur when CPS is used as intermediate representation), so optimizations and transformations formulated in terms of one immediately apply to the other.

Benefits

The primary usefulness of SSA comes from how it simultaneously simplifies and improves the results of a variety of compiler optimizations, by simplifying the properties of variables. For example, consider this piece of code:

 y := 1
 y := 2
 x := y

Humans can see that the first assignment is not necessary, and that the value of y being used in the third line comes from the second assignment of y. A program would have to perform reaching definition analysis to determine this. But if the program is in SSA form, both of these are immediate:

 y1 := 1
 y2 := 2
 x1 := y2

Compiler optimization algorithms which are either enabled or strongly enhanced by the use of SSA include:

Converting to SSA

Converting ordinary code into SSA form is primarily a simple matter of replacing the target of each assignment with a new variable, and replacing each use of a variable with the "version" of the variable reaching that point. For example, consider the following control flow graph:

An example control flow graph, before conversion to SSA

Notice that we could change the name on the left side of "x x - 3", and change the following uses of x to use that new name, and the program would still do the same thing. We exploit this in SSA by creating two new variables, x1 and x2, each of which is assigned only once. We likewise give distinguishing subscripts to all the other variables, and we get this:

An example control flow graph, partially converted to SSA

We've figured out which definition each use is referring to, except for one thing: the uses of y in the bottom block could be referring to either y1 or y2, depending on which way the control flow came from. So how do we know which one to use?

The answer is that we add a special statement, called a Φ (Phi) function, to the beginning of the last block. This statement will generate a new definition of y, y3, by "choosing" either y1 or y2, depending on which arrow control arrived from:

An example control flow graph, fully converted to SSA

Now, the uses of y in the last block can simply use y3, and they'll obtain the correct value either way. You might ask at this point, do we need to add a Φ function for x too? The answer is no; only one version of x, namely x2 is reaching this place, so there's no problem.

A more general question along the same lines is, given an arbitrary control flow graph, how can I tell where to insert Φ functions, and for what variables? This is a difficult question, but one that has an efficient solution that can be computed using a concept called dominance frontiers.

Note: the Φ functions are not actually implemented; instead, they're just markers for the compiler to place the value of all the variables, which are grouped together by the Φ function, in the same location in memory (or same register).

According to Kenny Zadeck[1] Φ functions were originally known as phoney functions while SSA was being developed at IBM Research in the 1980s. The formal name of Φ function was only adopted when the work was first published in an academic paper.

Computing minimal SSA using dominance frontiers

First, we need the concept of a dominator: we say that a node A strictly dominates a different node B in the control flow graph if it's impossible to reach B without passing through A first. This is useful, because if we ever reach B we know that any code in A has run. We say that A dominates B (B is dominated by A) if either A strictly dominates B or A = B.

Now we can define the dominance frontier: a node B is in the dominance frontier of a node A if A does not strictly dominate B, but does dominate some immediate predecessor of B (possibly node A is an immediate predecessor of B. Then, because any node dominates itself and node A dominates itself, node B is in the dominance frontier of node A.). From A's point of view, these are the nodes at which other control paths, which don't go through A, make their earliest appearance.

Dominance frontiers capture the precise places at which we need Φ functions: if the node A defines a certain variable, then that definition and that definition alone (or redefinitions) will reach every node A dominates. Only when we leave these nodes and enter the dominance frontier must we account for other flows bringing in other definitions of the same variable. Moreover, no other Φ functions are needed in the control flow graph to deal with A's definitions, and we can do with no less.

One algorithm for computing the dominance frontier set[2] is:

for each node b
    if the number of immediate predecessors of b ≥ 2
        for each p in immediate predecessors of b
            runner := p
            while runner ≠ idom(b)
                add b to runner’s dominance frontier set
                runner := idom(runner)

Note: in the code above, an immediate predecessor of node n is any node from which control is transferred to node n, and idom(b) is the node that immediately dominates node b (a singleton set).

There is an efficient algorithm for finding dominance frontiers of each node. This algorithm was originally described in Cytron et al. 1991.[3] Also useful is chapter 19 of the book "Modern compiler implementation in Java" by Andrew Appel (Cambridge University Press, 2002). See the paper for more details.

Keith D. Cooper, Timothy J. Harvey, and Ken Kennedy of Rice University describe an algorithm in their paper titled A Simple, Fast Dominance Algorithm.[2] The algorithm uses well-engineered data structures to improve performance.

Variations that reduce the number of Φ functions

"Minimal" SSA inserts the minimal number of Φ functions required to ensure that each name is assigned a value exactly once and that each reference (use) of a name in the original program can still refer to a unique name. (The latter requirement is needed to ensure that the compiler can write down a name for each operand in each operation.)

However, some of these Φ functions could be dead. For this reason, minimal SSA does not necessarily produce the fewest number of Φ functions that are needed by a specific procedure. For some types of analysis, these Φ functions are superfluous and can cause the analysis to run less efficiently.

Pruned SSA

Pruned SSA form is based on a simple observation: Φ functions are only needed for variables that are "live" after the Φ function. (Here, "live" means that the value is used along some path that begins at the Φ function in question.) If a variable is not live, the result of the Φ function cannot be used and the assignment by the Φ function is dead.

Construction of pruned SSA form uses live variable information in the Φ function insertion phase to decide whether a given Φ function is needed. If the original variable name isn't live at the Φ function insertion point, the Φ function isn't inserted.

Another possibility is to treat pruning as a dead code elimination problem. Then, a Φ function is live only if any use in the input program will be rewritten to it, or if it will be used as an argument in another Φ function. When entering SSA form, each use is rewritten to the nearest definition that dominates it. A Φ function will then be considered live as long as it is the nearest definition that dominates at least one use, or at least one argument of a live Φ.

Semi-pruned SSA

Semi-pruned SSA form [4] is an attempt to reduce the number of Φ functions without incurring the relatively high cost of computing live variable information. It is based on the following observation: if a variable is never live upon entry into a basic block, it never needs a Φ function. During SSA construction, Φ functions for any "block-local" variables are omitted.

Computing the set of block-local variables is a simpler and faster procedure than full live variable analysis, making semi-pruned SSA form more efficient to compute than pruned SSA form. On the other hand, semi-pruned SSA form will contain more Φ functions.

Converting out of SSA form

SSA form is not normally used for direct execution (although it is possible to interpret SSA[5]), and it is frequently used "on top of" another IR with which it remains in direct correspondence. This can be accomplished by "constructing" SSA as a set of functions which map between parts of the existing IR (basic blocks, instructions, operands, etc.) and its SSA counterpart. When the SSA form is no longer needed, these mapping functions may be discarded, leaving only the now-optimized IR.

Performing optimizations on SSA form usually leads to entangled SSA-Webs, meaning there are phi instructions whose operands do not all have the same root operand. In such cases color-out algorithms are used to come out of SSA. Naive algorithms introduce a copy along each predecessor path which caused a source of different root symbol to be put in phi than the destination of phi. There are multiple algorithms for coming out of SSA with fewer copies, most use interference graphs or some approximation of it to do copy coalescing.

Extensions

Extensions to SSA form can be divided into two categories.

Renaming scheme extensions alter the renaming criterion. Recall that SSA form renames each variable when it is assigned a value. Alternative schemes include static single use form (which renames each variable at each statement when it is used) and static single information form (which renames each variable when it is assigned a value, and at the post-dominance frontier).

Feature-specific extensions retain the single assignment property for variables, but incorporate new semantics to model additional features. Some feature-specific extensions model high-level programming language features like arrays, objects and aliased pointers. Other feature-specific extensions model low-level architectural features like speculation and predication.

Compilers using SSA form

SSA form is a relatively recent development in the compiler community. As such, many older compilers only use SSA form for some part of the compilation or optimization process, but most do not rely on it. Examples of compilers that rely heavily on SSA form include:

  • The ETH Oberon-2 compiler was one of the first public projects to incorporate "GSA", a variant of SSA.
  • The LLVM Compiler Infrastructure uses SSA form for all scalar register values (everything except memory) in its primary code representation. SSA form is only eliminated once register allocation occurs, late in the compile process (often at link time).
  • The Open64 compiler uses SSA form in its global scalar optimizer, though the code is brought into SSA form before and taken out of SSA form afterwards. Open64 uses extensions to SSA form to represent memory in SSA form as well as scalar values.
  • As of version 4 (released in April 2005) GCC, the GNU Compiler Collection, makes extensive use of SSA. The frontends generate "GENERIC" code which is then converted into "GIMPLE" code by the "gimplifier". High-level optimizations are then applied on the SSA form of "GIMPLE". The resulting optimized intermediate code is then translated into RTL, on which low-level optimizations are applied. The architecture-specific backends finally turn RTL into assembly language.
  • IBM's open source adaptive Java virtual machine, Jikes RVM, uses extended Array SSA, an extension of SSA that allows analysis of scalars, arrays, and object fields in a unified framework. Extended Array SSA analysis is only enabled at the maximum optimization level, which is applied to the most frequently executed portions of code.
  • In 2002, researchers modified IBM's JikesRVM (named Jalapeño at the time) to run both standard Java byte-code and a typesafe SSA (SafeTSA) byte-code class files, and demonstrated significant performance benefits to using the SSA byte-code.
  • Oracle's Java HotSpot Virtual Machine uses an SSA-based intermediate language in its JIT compiler.
  • Mono uses SSA in its JIT compiler called Mini.
  • jackcc is an open-source compiler for the academic instruction set Jackal 3.0. It uses a simple 3-operand code with SSA for its intermediate representation. As an interesting variant, it replaces Φ functions with a so-called SAME instruction, which instructs the register allocator to place the two live ranges into the same physical register.
  • Although not a compiler, the Boomerang decompiler uses SSA form in its internal representation. SSA is used to simplify expression propagation, identifying parameters and returns, preservation analysis, and more.
  • Portable.NET uses SSA in its JIT compiler.
  • libFirm a completely graph based SSA intermediate representation for compilers. libFirm uses SSA form for all scalar register values until code generation by use of an SSA-aware register allocator.
  • The Illinois Concert Compiler circa 1994[6] used a variant of SSA called SSU (Static Single Use) which renames each variable when it is assigned a value, and in each conditional context in which that variable is used; essentially the static single information form mentioned above. The SSU form is documented in John Plevyak's Ph.D Thesis.
  • PyPy uses a linear SSA representation for traces in its JIT compiler.
  • The Standard ML compiler MLton uses SSA in one of its intermediate languages.
  • LuaJIT makes heavy use of SSA-based optimizations.[7]

See also

References

Notes

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General references

  • 20 year-old Real Estate Agent Rusty from Saint-Paul, has hobbies and interests which includes monopoly, property developers in singapore and poker. Will soon undertake a contiki trip that may include going to the Lower Valley of the Omo.

    My blog: http://www.primaboinca.com/view_profile.php?userid=5889534 Also available in Java (ISBN 0-521-82060-X 2002) and C (ISBN 0-521-60765-5, 1998) versions.
  • 20 year-old Real Estate Agent Rusty from Saint-Paul, has hobbies and interests which includes monopoly, property developers in singapore and poker. Will soon undertake a contiki trip that may include going to the Lower Valley of the Omo.

    My blog: http://www.primaboinca.com/view_profile.php?userid=5889534
  • 20 year-old Real Estate Agent Rusty from Saint-Paul, has hobbies and interests which includes monopoly, property developers in singapore and poker. Will soon undertake a contiki trip that may include going to the Lower Valley of the Omo.

    My blog: http://www.primaboinca.com/view_profile.php?userid=5889534
  • One of the biggest reasons investing in a Singapore new launch is an effective things is as a result of it is doable to be lent massive quantities of money at very low interest rates that you should utilize to purchase it. Then, if property values continue to go up, then you'll get a really high return on funding (ROI). Simply make sure you purchase one of the higher properties, reminiscent of the ones at Fernvale the Riverbank or any Singapore landed property Get Earnings by means of Renting

    In its statement, the singapore property listing - website link, government claimed that the majority citizens buying their first residence won't be hurt by the new measures. Some concessions can even be prolonged to chose teams of consumers, similar to married couples with a minimum of one Singaporean partner who are purchasing their second property so long as they intend to promote their first residential property. Lower the LTV limit on housing loans granted by monetary establishments regulated by MAS from 70% to 60% for property purchasers who are individuals with a number of outstanding housing loans on the time of the brand new housing purchase. Singapore Property Measures - 30 August 2010 The most popular seek for the number of bedrooms in Singapore is 4, followed by 2 and three. Lush Acres EC @ Sengkang

    Discover out more about real estate funding in the area, together with info on international funding incentives and property possession. Many Singaporeans have been investing in property across the causeway in recent years, attracted by comparatively low prices. However, those who need to exit their investments quickly are likely to face significant challenges when trying to sell their property – and could finally be stuck with a property they can't sell. Career improvement programmes, in-house valuation, auctions and administrative help, venture advertising and marketing, skilled talks and traisning are continuously planned for the sales associates to help them obtain better outcomes for his or her shoppers while at Knight Frank Singapore. No change Present Rules

    Extending the tax exemption would help. The exemption, which may be as a lot as $2 million per family, covers individuals who negotiate a principal reduction on their existing mortgage, sell their house short (i.e., for lower than the excellent loans), or take part in a foreclosure course of. An extension of theexemption would seem like a common-sense means to assist stabilize the housing market, but the political turmoil around the fiscal-cliff negotiations means widespread sense could not win out. Home Minority Chief Nancy Pelosi (D-Calif.) believes that the mortgage relief provision will be on the table during the grand-cut price talks, in response to communications director Nadeam Elshami. Buying or promoting of blue mild bulbs is unlawful.

    A vendor's stamp duty has been launched on industrial property for the primary time, at rates ranging from 5 per cent to 15 per cent. The Authorities might be trying to reassure the market that they aren't in opposition to foreigners and PRs investing in Singapore's property market. They imposed these measures because of extenuating components available in the market." The sale of new dual-key EC models will even be restricted to multi-generational households only. The models have two separate entrances, permitting grandparents, for example, to dwell separately. The vendor's stamp obligation takes effect right this moment and applies to industrial property and plots which might be offered inside three years of the date of buy. JLL named Best Performing Property Brand for second year running

    The data offered is for normal info purposes only and isn't supposed to be personalised investment or monetary advice. Motley Fool Singapore contributor Stanley Lim would not personal shares in any corporations talked about. Singapore private home costs increased by 1.eight% within the fourth quarter of 2012, up from 0.6% within the earlier quarter. Resale prices of government-built HDB residences which are usually bought by Singaporeans, elevated by 2.5%, quarter on quarter, the quickest acquire in five quarters. And industrial property, prices are actually double the levels of three years ago. No withholding tax in the event you sell your property. All your local information regarding vital HDB policies, condominium launches, land growth, commercial property and more

    There are various methods to go about discovering the precise property. Some local newspapers (together with the Straits Instances ) have categorised property sections and many local property brokers have websites. Now there are some specifics to consider when buying a 'new launch' rental. Intended use of the unit Every sale begins with 10 p.c low cost for finish of season sale; changes to 20 % discount storewide; follows by additional reduction of fiftyand ends with last discount of 70 % or extra. Typically there is even a warehouse sale or transferring out sale with huge mark-down of costs for stock clearance. Deborah Regulation from Expat Realtor shares her property market update, plus prime rental residences and houses at the moment available to lease Esparina EC @ Sengkang
  • One of the biggest reasons investing in a Singapore new launch is an effective things is as a result of it is doable to be lent massive quantities of money at very low interest rates that you should utilize to purchase it. Then, if property values continue to go up, then you'll get a really high return on funding (ROI). Simply make sure you purchase one of the higher properties, reminiscent of the ones at Fernvale the Riverbank or any Singapore landed property Get Earnings by means of Renting

    In its statement, the singapore property listing - website link, government claimed that the majority citizens buying their first residence won't be hurt by the new measures. Some concessions can even be prolonged to chose teams of consumers, similar to married couples with a minimum of one Singaporean partner who are purchasing their second property so long as they intend to promote their first residential property. Lower the LTV limit on housing loans granted by monetary establishments regulated by MAS from 70% to 60% for property purchasers who are individuals with a number of outstanding housing loans on the time of the brand new housing purchase. Singapore Property Measures - 30 August 2010 The most popular seek for the number of bedrooms in Singapore is 4, followed by 2 and three. Lush Acres EC @ Sengkang

    Discover out more about real estate funding in the area, together with info on international funding incentives and property possession. Many Singaporeans have been investing in property across the causeway in recent years, attracted by comparatively low prices. However, those who need to exit their investments quickly are likely to face significant challenges when trying to sell their property – and could finally be stuck with a property they can't sell. Career improvement programmes, in-house valuation, auctions and administrative help, venture advertising and marketing, skilled talks and traisning are continuously planned for the sales associates to help them obtain better outcomes for his or her shoppers while at Knight Frank Singapore. No change Present Rules

    Extending the tax exemption would help. The exemption, which may be as a lot as $2 million per family, covers individuals who negotiate a principal reduction on their existing mortgage, sell their house short (i.e., for lower than the excellent loans), or take part in a foreclosure course of. An extension of theexemption would seem like a common-sense means to assist stabilize the housing market, but the political turmoil around the fiscal-cliff negotiations means widespread sense could not win out. Home Minority Chief Nancy Pelosi (D-Calif.) believes that the mortgage relief provision will be on the table during the grand-cut price talks, in response to communications director Nadeam Elshami. Buying or promoting of blue mild bulbs is unlawful.

    A vendor's stamp duty has been launched on industrial property for the primary time, at rates ranging from 5 per cent to 15 per cent. The Authorities might be trying to reassure the market that they aren't in opposition to foreigners and PRs investing in Singapore's property market. They imposed these measures because of extenuating components available in the market." The sale of new dual-key EC models will even be restricted to multi-generational households only. The models have two separate entrances, permitting grandparents, for example, to dwell separately. The vendor's stamp obligation takes effect right this moment and applies to industrial property and plots which might be offered inside three years of the date of buy. JLL named Best Performing Property Brand for second year running

    The data offered is for normal info purposes only and isn't supposed to be personalised investment or monetary advice. Motley Fool Singapore contributor Stanley Lim would not personal shares in any corporations talked about. Singapore private home costs increased by 1.eight% within the fourth quarter of 2012, up from 0.6% within the earlier quarter. Resale prices of government-built HDB residences which are usually bought by Singaporeans, elevated by 2.5%, quarter on quarter, the quickest acquire in five quarters. And industrial property, prices are actually double the levels of three years ago. No withholding tax in the event you sell your property. All your local information regarding vital HDB policies, condominium launches, land growth, commercial property and more

    There are various methods to go about discovering the precise property. Some local newspapers (together with the Straits Instances ) have categorised property sections and many local property brokers have websites. Now there are some specifics to consider when buying a 'new launch' rental. Intended use of the unit Every sale begins with 10 p.c low cost for finish of season sale; changes to 20 % discount storewide; follows by additional reduction of fiftyand ends with last discount of 70 % or extra. Typically there is even a warehouse sale or transferring out sale with huge mark-down of costs for stock clearance. Deborah Regulation from Expat Realtor shares her property market update, plus prime rental residences and houses at the moment available to lease Esparina EC @ Sengkang
  • One of the biggest reasons investing in a Singapore new launch is an effective things is as a result of it is doable to be lent massive quantities of money at very low interest rates that you should utilize to purchase it. Then, if property values continue to go up, then you'll get a really high return on funding (ROI). Simply make sure you purchase one of the higher properties, reminiscent of the ones at Fernvale the Riverbank or any Singapore landed property Get Earnings by means of Renting

    In its statement, the singapore property listing - website link, government claimed that the majority citizens buying their first residence won't be hurt by the new measures. Some concessions can even be prolonged to chose teams of consumers, similar to married couples with a minimum of one Singaporean partner who are purchasing their second property so long as they intend to promote their first residential property. Lower the LTV limit on housing loans granted by monetary establishments regulated by MAS from 70% to 60% for property purchasers who are individuals with a number of outstanding housing loans on the time of the brand new housing purchase. Singapore Property Measures - 30 August 2010 The most popular seek for the number of bedrooms in Singapore is 4, followed by 2 and three. Lush Acres EC @ Sengkang

    Discover out more about real estate funding in the area, together with info on international funding incentives and property possession. Many Singaporeans have been investing in property across the causeway in recent years, attracted by comparatively low prices. However, those who need to exit their investments quickly are likely to face significant challenges when trying to sell their property – and could finally be stuck with a property they can't sell. Career improvement programmes, in-house valuation, auctions and administrative help, venture advertising and marketing, skilled talks and traisning are continuously planned for the sales associates to help them obtain better outcomes for his or her shoppers while at Knight Frank Singapore. No change Present Rules

    Extending the tax exemption would help. The exemption, which may be as a lot as $2 million per family, covers individuals who negotiate a principal reduction on their existing mortgage, sell their house short (i.e., for lower than the excellent loans), or take part in a foreclosure course of. An extension of theexemption would seem like a common-sense means to assist stabilize the housing market, but the political turmoil around the fiscal-cliff negotiations means widespread sense could not win out. Home Minority Chief Nancy Pelosi (D-Calif.) believes that the mortgage relief provision will be on the table during the grand-cut price talks, in response to communications director Nadeam Elshami. Buying or promoting of blue mild bulbs is unlawful.

    A vendor's stamp duty has been launched on industrial property for the primary time, at rates ranging from 5 per cent to 15 per cent. The Authorities might be trying to reassure the market that they aren't in opposition to foreigners and PRs investing in Singapore's property market. They imposed these measures because of extenuating components available in the market." The sale of new dual-key EC models will even be restricted to multi-generational households only. The models have two separate entrances, permitting grandparents, for example, to dwell separately. The vendor's stamp obligation takes effect right this moment and applies to industrial property and plots which might be offered inside three years of the date of buy. JLL named Best Performing Property Brand for second year running

    The data offered is for normal info purposes only and isn't supposed to be personalised investment or monetary advice. Motley Fool Singapore contributor Stanley Lim would not personal shares in any corporations talked about. Singapore private home costs increased by 1.eight% within the fourth quarter of 2012, up from 0.6% within the earlier quarter. Resale prices of government-built HDB residences which are usually bought by Singaporeans, elevated by 2.5%, quarter on quarter, the quickest acquire in five quarters. And industrial property, prices are actually double the levels of three years ago. No withholding tax in the event you sell your property. All your local information regarding vital HDB policies, condominium launches, land growth, commercial property and more

    There are various methods to go about discovering the precise property. Some local newspapers (together with the Straits Instances ) have categorised property sections and many local property brokers have websites. Now there are some specifics to consider when buying a 'new launch' rental. Intended use of the unit Every sale begins with 10 p.c low cost for finish of season sale; changes to 20 % discount storewide; follows by additional reduction of fiftyand ends with last discount of 70 % or extra. Typically there is even a warehouse sale or transferring out sale with huge mark-down of costs for stock clearance. Deborah Regulation from Expat Realtor shares her property market update, plus prime rental residences and houses at the moment available to lease Esparina EC @ Sengkang
  • Many property agents need to declare for the PIC grant in Singapore. However, not all of them know find out how to do the correct process for getting this PIC scheme from the IRAS. There are a number of steps that you need to do before your software can be approved.

    Naturally, you will have to pay a safety deposit and that is usually one month rent for annually of the settlement. That is the place your good religion deposit will likely be taken into account and will kind part or all of your security deposit. Anticipate to have a proportionate amount deducted out of your deposit if something is discovered to be damaged if you move out. It's best to you'll want to test the inventory drawn up by the owner, which can detail all objects in the property and their condition. If you happen to fail to notice any harm not already mentioned within the inventory before transferring in, you danger having to pay for it yourself.

    In case you are in search of an actual estate or Singapore property agent on-line, you simply should belief your intuition. It's because you do not know which agent is nice and which agent will not be. Carry out research on several brokers by looking out the internet. As soon as if you end up positive that a selected agent is dependable and reliable, you can choose to utilize his partnerise in finding you a home in Singapore. Most of the time, a property agent is taken into account to be good if he or she locations the contact data on his website. This may mean that the agent does not mind you calling them and asking them any questions relating to new properties in singapore in Singapore. After chatting with them you too can see them in their office after taking an appointment.

    Have handed an trade examination i.e Widespread Examination for House Brokers (CEHA) or Actual Property Agency (REA) examination, or equal; Exclusive brokers are extra keen to share listing information thus making certain the widest doable coverage inside the real estate community via Multiple Listings and Networking. Accepting a severe provide is simpler since your agent is totally conscious of all advertising activity related with your property. This reduces your having to check with a number of agents for some other offers. Price control is easily achieved. Paint work in good restore-discuss with your Property Marketing consultant if main works are still to be done. Softening in residential property prices proceed, led by 2.8 per cent decline within the index for Remainder of Central Region

    Once you place down the one per cent choice price to carry down a non-public property, it's important to accept its situation as it is whenever you move in – faulty air-con, choked rest room and all. Get round this by asking your agent to incorporate a ultimate inspection clause within the possibility-to-buy letter. HDB flat patrons routinely take pleasure in this security net. "There's a ultimate inspection of the property two days before the completion of all HDB transactions. If the air-con is defective, you can request the seller to repair it," says Kelvin.

    15.6.1 As the agent is an intermediary, generally, as soon as the principal and third party are introduced right into a contractual relationship, the agent drops out of the image, subject to any problems with remuneration or indemnification that he could have against the principal, and extra exceptionally, against the third occasion. Generally, agents are entitled to be indemnified for all liabilities reasonably incurred within the execution of the brokers´ authority.

    To achieve the very best outcomes, you must be always updated on market situations, including past transaction information and reliable projections. You could review and examine comparable homes that are currently available in the market, especially these which have been sold or not bought up to now six months. You'll be able to see a pattern of such report by clicking here It's essential to defend yourself in opposition to unscrupulous patrons. They are often very skilled in using highly unethical and manipulative techniques to try and lure you into a lure. That you must also protect your self, your loved ones, and personal belongings as you'll be serving many strangers in your home. Sign a listing itemizing of all of the objects provided by the proprietor, together with their situation. HSR Prime Recruiter 2010

External links

  1. Zadeck, F. Kenneth, Presentation on the History of SSA at the SSA'09 Seminar, Autrans, France, April 2009
  2. 2.0 2.1 Template:Cite paper
  3. One of the biggest reasons investing in a Singapore new launch is an effective things is as a result of it is doable to be lent massive quantities of money at very low interest rates that you should utilize to purchase it. Then, if property values continue to go up, then you'll get a really high return on funding (ROI). Simply make sure you purchase one of the higher properties, reminiscent of the ones at Fernvale the Riverbank or any Singapore landed property Get Earnings by means of Renting

    In its statement, the singapore property listing - website link, government claimed that the majority citizens buying their first residence won't be hurt by the new measures. Some concessions can even be prolonged to chose teams of consumers, similar to married couples with a minimum of one Singaporean partner who are purchasing their second property so long as they intend to promote their first residential property. Lower the LTV limit on housing loans granted by monetary establishments regulated by MAS from 70% to 60% for property purchasers who are individuals with a number of outstanding housing loans on the time of the brand new housing purchase. Singapore Property Measures - 30 August 2010 The most popular seek for the number of bedrooms in Singapore is 4, followed by 2 and three. Lush Acres EC @ Sengkang

    Discover out more about real estate funding in the area, together with info on international funding incentives and property possession. Many Singaporeans have been investing in property across the causeway in recent years, attracted by comparatively low prices. However, those who need to exit their investments quickly are likely to face significant challenges when trying to sell their property – and could finally be stuck with a property they can't sell. Career improvement programmes, in-house valuation, auctions and administrative help, venture advertising and marketing, skilled talks and traisning are continuously planned for the sales associates to help them obtain better outcomes for his or her shoppers while at Knight Frank Singapore. No change Present Rules

    Extending the tax exemption would help. The exemption, which may be as a lot as $2 million per family, covers individuals who negotiate a principal reduction on their existing mortgage, sell their house short (i.e., for lower than the excellent loans), or take part in a foreclosure course of. An extension of theexemption would seem like a common-sense means to assist stabilize the housing market, but the political turmoil around the fiscal-cliff negotiations means widespread sense could not win out. Home Minority Chief Nancy Pelosi (D-Calif.) believes that the mortgage relief provision will be on the table during the grand-cut price talks, in response to communications director Nadeam Elshami. Buying or promoting of blue mild bulbs is unlawful.

    A vendor's stamp duty has been launched on industrial property for the primary time, at rates ranging from 5 per cent to 15 per cent. The Authorities might be trying to reassure the market that they aren't in opposition to foreigners and PRs investing in Singapore's property market. They imposed these measures because of extenuating components available in the market." The sale of new dual-key EC models will even be restricted to multi-generational households only. The models have two separate entrances, permitting grandparents, for example, to dwell separately. The vendor's stamp obligation takes effect right this moment and applies to industrial property and plots which might be offered inside three years of the date of buy. JLL named Best Performing Property Brand for second year running

    The data offered is for normal info purposes only and isn't supposed to be personalised investment or monetary advice. Motley Fool Singapore contributor Stanley Lim would not personal shares in any corporations talked about. Singapore private home costs increased by 1.eight% within the fourth quarter of 2012, up from 0.6% within the earlier quarter. Resale prices of government-built HDB residences which are usually bought by Singaporeans, elevated by 2.5%, quarter on quarter, the quickest acquire in five quarters. And industrial property, prices are actually double the levels of three years ago. No withholding tax in the event you sell your property. All your local information regarding vital HDB policies, condominium launches, land growth, commercial property and more

    There are various methods to go about discovering the precise property. Some local newspapers (together with the Straits Instances ) have categorised property sections and many local property brokers have websites. Now there are some specifics to consider when buying a 'new launch' rental. Intended use of the unit Every sale begins with 10 p.c low cost for finish of season sale; changes to 20 % discount storewide; follows by additional reduction of fiftyand ends with last discount of 70 % or extra. Typically there is even a warehouse sale or transferring out sale with huge mark-down of costs for stock clearance. Deborah Regulation from Expat Realtor shares her property market update, plus prime rental residences and houses at the moment available to lease Esparina EC @ Sengkang
  4. Template:Cite paper
  5. Template:Cite paper
  6. Template:Cite web
  7. Template:Cite web