Hello again,<br><br>I want to ask you some piece of advice if it is possible.<br><br>I tried methods related to point 1) suggested by you, but I still have problems of finding dependencies. What exactly I want to do:<br><br>
I have a chain like : Alloca -> Load(1) -> ... -> Computation where the variable
might be changed -> Store(new_var) -> ... -> Load(n)<br><br>Computation where the variable is changed = means that : I might have Alloca(a), c=a+7000*b[32], Load(c)...ICMP(c, ...)<br><br>I want to get the corresponding Alloca from every Load (corresponding from the point of view of the variable used, meaning that the Load is using a variables based/dependent on the Alloca or Allocas).<br>
<br><br>First, I tried the point 1) suggested by you. AliasSetTracker uses methods from AliasAnalysis, so I tried to use directly those methods.<br>After I see all the must-aliases, I categorize them into 2 :<br>
1. category A : aliases with allocas<br>2. category B: aliases without allocas<br>For category A, is straight ahead for what I need.<br>For
category B, I check if there is an instruction where the variable is
used also from an instruction from the aliases from category A. If it is, it is ok.<br><br>But the following given me no result at all (and they should, I have dependencies - meaning Load j is used multiple times in my code, so the pointers should be must-alias) I have all the Load instructions in an array loadInstrArray. :<br>
<br>1. if( AA.isMustAlias(Loci,Locj) ) - no result<br>2. if( AA.alias(Loci,Locj) ) - wrong results, like "LOAD %2 = load i32* %j, align 4 IS DEPENDENT ON %3 = load i32* %c, align 4"<br> where j is totally independent from c<br>
3. if( AA.getModRefInfo(allocaInstrArray[j],Loci) ) - no result<br><br><br>Second, I tried to use methods from DependencyAnalysis class. <br><br>1. if (DA.depends(loadInstrArray[i],loadInstrArray[j],false)) - no result<br>
<br><br>Third, I tried methods from MemoryDependenceAnalysis class - the existing pass <a href="http://llvm.org/docs/doxygen/html/MemDepPrinter_8cpp_source.html">http://llvm.org/docs/doxygen/html/MemDepPrinter_8cpp_source.html</a> . <br>
<br>1. I have wrong results, like : %1 = load i32* %j, align 4 IS Clobber FROM: store i32 0, i32* %c, align 4<br>2. then I tried to get only DEF (not clobber), since I only need to see the correspondent Alloca for every Load. I don't have any result for Loads. I also checked with getDef() method, so Loads are dependent on themselves<br>
3. I have to mention that I commented line 00131, since I had an unsolved segfault and not the parameters are the problem.<br><br><br>Fourth, I took a look in to DSNodeEquivs pass suggested by you. I think that getMemberForValue() method I can use. To be honest, I tried to focus on the classes that are already existent on LLVM.<br>
<br>What do you think I should focus on, what approach is better to take into account and what to eliminate?<br><br>Thank you a lot for your time !<br><br><br><br><div class="gmail_quote">On Tue, Jan 22, 2013 at 4:57 PM, John Criswell <span dir="ltr"><<a href="mailto:criswell@illinois.edu" target="_blank">criswell@illinois.edu</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div bgcolor="#FFFFFF" text="#000000"><div class="im">
<div>On 1/21/13 5:22 AM, Alexandru Ionut
Diaconescu wrote:<br>
</div>
<blockquote type="cite">
Hello everyone !<br>
<br clear="all">
I am trying to determine for certain Load instructions from my
pass their corresponding Alloca instructions (that can be in other
previous blocks). The chain can be something like :
`TargetLoad(var) -> other stores/loads that use var (or
dependencies on var) -> alloca(var).` , linked on several basic
blocks. Do you know how can I do it?<br>
</blockquote>
<br></div>
This sounds like an alias analysis query that you're trying to do.
There are a couple of options:<br>
<br>
1) Cycle through all the allocas and ask if they alias with the
loaded pointer. You can use any of the alias analysis
implementations available for LLVM. Alternatively, I think LLVM
might have a class called AliasSetTracker which can do something
similar for you.<br>
<br>
2) Use DSA from the poolalloc project. The DSNodeEquivs pass can be
used to determine if a load and an alloca alias. Depending on your
situation, DSA may give better or worse results than LLVM's current
alias analysis algorithms. I would think that DSA can do a better
job for pointers stored into memory locations. <br>
<br>
-- John T.<br>
<br>
<br>
</div>
</blockquote></div><br><br clear="all"><br>-- <br><font style="background-color:rgb(255,255,255);color:rgb(153,153,153)">Best regards,</font><br style="background-color:rgb(255,255,255);color:rgb(153,153,153)"><font style="background-color:rgb(255,255,255);color:rgb(153,153,153)">Alexandru Ionut Diaconescu</font><br>