[LLVMdev] writing an alias analysis pass?

[Jingyue Wu]

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?


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