[LLVMdev] writing an alias analysis pass?

[Matthew O'Connor]

On Mon, Apr 28, 2014 at 10:46 PM, Chen Li <meloli87 at gmail.com> wrote:

> Hi Matthew,
>
> Did you add your alias analysis pass initializeEverythingMustAliasPass()
> into llvm::initializeAnalysis(PassRegistry &Registry) {} ?
> This will initialize it linked into the Analysis library.
>
> thanks,
> chen
>

I want to be able to load my pass from an external library & not have it
compiled into opt.


> On Apr 28, 2014, at 8:43 PM, Jingyue Wu <jingyue at google.com> wrote:
>
>
>
>
> On Thu, Apr 24, 2014 at 4:38 PM, Matthew O'Connor <
> thegreendragon at gmail.com> wrote:
>
>> Hi,
>>
>> I'm attempting to do some alias analysis & other memory inspection. I've
>> written a pointless AliasAnalysis pass (that says everything must alias) to
>> attempt to verify that my pass is getting picked up & run by opt.
>>
>> I run opt with: opt -load ~/Applications/llvm/lib/MustAA.so -must-aa
>> -aa-eval -debug < trace0.ll
>>
>> I see my pass being initialized, but never being called (I see only may
>> alias results).
>>
>> Any ideas as to what to do to debug this? Or what I'm missing? I've read
>> through http://llvm.org/docs/AliasAnalysis.html and don't see anything
>> that I'm missing.
>>
>> Thanks,
>> Matthew
>>
>> P.S. Here's the full source code of my pass:
>>
>> #define DEBUG_TYPE "must-aa"
>> #include "llvm/Pass.h"
>> #include "llvm/Analysis/AliasAnalysis.h"
>> #include "llvm/Support/raw_ostream.h"
>> #include "llvm/Support/Debug.h"
>> using namespace llvm;
>>
>> namespace {
>> struct EverythingMustAlias : public ImmutablePass, public AliasAnalysis {
>>   static char ID;
>>   EverythingMustAlias() : ImmutablePass(ID) {}
>>
>>   virtual void initializePass() {
>>     DEBUG(dbgs() << "Initializing everything-must-alias\n");
>>     InitializeAliasAnalysis(this);
>>   }
>>
>>   virtual void getAnalysisUsage(AnalysisUsage &AU) const {
>>     AliasAnalysis::getAnalysisUsage(AU);
>>     AU.setPreservesAll();
>>   }
>>
>>   virtual AliasResult alias(const Location &LocA, const Location &LocB) {
>>     DEBUG(dbgs() << "Everything must alias!\n");
>>     return AliasAnalysis::MustAlias;
>>   }
>> };
>> }
>>
>> namespace llvm {
>> void initializeEverythingMustAliasPass(PassRegistry &Registry);
>> }
>>
>> char EverythingMustAlias::ID = 0;
>> static RegisterPass<EverythingMustAlias> A("must-aa", "Everything must
>> alias");
>>
>
> static RegisterPass<EverythingMustAlias> A("must-aa", "Everything must
> alias", false, true);
>
> Can you try this?
>
>
I changed "static RegisterPass<EverythingMustAlias> A("must-aa",
"Everything must alias");"
to
"static RegisterPass<
EverythingMustAlias> A("must-aa", "Everything must alias", false, true);"
and am seeing the same behavior.

 INITIALIZE_AG_PASS(EverythingMustAlias, AliasAnalysis, "must-aa",
>>                    "Everything must alias", false, true, false)
>>
>>
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>>
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