[llvm] 931b606 - [BasicAA] Handle assumes with operand bundles

[Nikita Popov via llvm-commits]

On Tue, Mar 23, 2021 at 10:21 PM Philip Reames <listmail at philipreames.com>
wrote:

> This doesn't seem like the right fix.  We conservatively report operand
> bundles allowing reads for *unknown* bundle types.  The assume bundle
> type should have well defined semantics and could be explicitly
> whitelisted.
>
> Philip
>

I believe the assume operand bundles are somewhat special and distinct from
other bundles, in that they only apply to assumes, and in that they are not
explicitly enumerated. An operand bundle on an assume simply corresponds to
the attribute of the same name.

Regards,
Nikita


> On 3/23/21 1:21 PM, Nikita Popov via llvm-commits wrote:
> > Author: Nikita Popov
> > Date: 2021-03-23T21:21:19+01:00
> > New Revision: 931b6066acc597e680b8df25521a2f83b40dfaae
> >
> > URL:
> https://github.com/llvm/llvm-project/commit/931b6066acc597e680b8df25521a2f83b40dfaae
> > DIFF:
> https://github.com/llvm/llvm-project/commit/931b6066acc597e680b8df25521a2f83b40dfaae.diff
> >
> > LOG: [BasicAA] Handle assumes with operand bundles
> >
> > This fixes a regression reported on D99022: If a call has operand
> > bundles, then the inaccessiblememonly attribute on the function
> > will be ignored, as operand bundles can affect modref behavior in
> > the general case. However, for assume operand bundles in particular
> > this is not the case.
> >
> > Adjust getModRefBehavior() to always report inaccessiblememonly
> > for assumes, regardless of presence of operand bundles.
> >
> > Added:
> >
> >
> > Modified:
> >      llvm/lib/Analysis/BasicAliasAnalysis.cpp
> >      llvm/test/Analysis/BasicAA/assume.ll
> >
> > Removed:
> >
> >
> >
> >
> ################################################################################
> > diff  --git a/llvm/lib/Analysis/BasicAliasAnalysis.cpp
> b/llvm/lib/Analysis/BasicAliasAnalysis.cpp
> > index 86362f770e2d4..65117d82a81ce 100644
> > --- a/llvm/lib/Analysis/BasicAliasAnalysis.cpp
> > +++ b/llvm/lib/Analysis/BasicAliasAnalysis.cpp
> > @@ -672,12 +672,22 @@ bool BasicAAResult::pointsToConstantMemory(const
> MemoryLocation &Loc,
> >     return Worklist.empty();
> >   }
> >
> > +static bool isIntrinsicCall(const CallBase *Call, Intrinsic::ID IID) {
> > +  const IntrinsicInst *II = dyn_cast<IntrinsicInst>(Call);
> > +  return II && II->getIntrinsicID() == IID;
> > +}
> > +
> >   /// Returns the behavior when calling the given call site.
> >   FunctionModRefBehavior BasicAAResult::getModRefBehavior(const CallBase
> *Call) {
> >     if (Call->doesNotAccessMemory())
> >       // Can't do better than this.
> >       return FMRB_DoesNotAccessMemory;
> >
> > +  // The assume intrinsic can have operand bundles, but still only
> accesses
> > +  // inaccessible memory in that case (to maintain control
> dependencies).
> > +  if (isIntrinsicCall(Call, Intrinsic::assume))
> > +    return FMRB_OnlyAccessesInaccessibleMem;
> > +
> >     FunctionModRefBehavior Min = FMRB_UnknownModRefBehavior;
> >
> >     // If the callsite knows it only reads memory, don't return worse
> > @@ -771,11 +781,6 @@ ModRefInfo BasicAAResult::getArgModRefInfo(const
> CallBase *Call,
> >     return AAResultBase::getArgModRefInfo(Call, ArgIdx);
> >   }
> >
> > -static bool isIntrinsicCall(const CallBase *Call, Intrinsic::ID IID) {
> > -  const IntrinsicInst *II = dyn_cast<IntrinsicInst>(Call);
> > -  return II && II->getIntrinsicID() == IID;
> > -}
> > -
> >   #ifndef NDEBUG
> >   static const Function *getParent(const Value *V) {
> >     if (const Instruction *inst = dyn_cast<Instruction>(V)) {
> >
> > diff  --git a/llvm/test/Analysis/BasicAA/assume.ll
> b/llvm/test/Analysis/BasicAA/assume.ll
> > index 4b268836cc49e..bc6be3ef0157e 100644
> > --- a/llvm/test/Analysis/BasicAA/assume.ll
> > +++ b/llvm/test/Analysis/BasicAA/assume.ll
> > @@ -29,12 +29,12 @@ define void @test2(i8* %P, i8* %Q) nounwind ssp {
> >   ; CHECK-LABEL: Function: test2:
> >
> >   ; CHECK: MayAlias:  i8* %P, i8* %Q
> > -; CHECK: Both ModRef:  Ptr: i8* %P   <->  tail call void
> @llvm.assume(i1 true) [ "nonnull"(i8* %P) ]
> > -; CHECK: Both ModRef:  Ptr: i8* %Q   <->  tail call void
> @llvm.assume(i1 true) [ "nonnull"(i8* %P) ]
> > +; CHECK: NoModRef:  Ptr: i8* %P      <->  tail call void
> @llvm.assume(i1 true) [ "nonnull"(i8* %P) ]
> > +; CHECK: NoModRef:  Ptr: i8* %Q      <->  tail call void
> @llvm.assume(i1 true) [ "nonnull"(i8* %P) ]
> >   ; CHECK: Both ModRef:  Ptr: i8* %P  <->  tail call void
> @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false)
> >   ; CHECK: Both ModRef:  Ptr: i8* %Q  <->  tail call void
> @llvm.memcpy.p0i8.p0i8.i64(i8* %P, i8* %Q, i64 12, i1 false)
> > -; CHECK: Both ModRef:   tail call void @llvm.assume(i1 true) [
> "nonnull"(i8* %P) ] <->   tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P,
> i8* %Q, i64 12, i1 false)
> > -; CHECK: Both ModRef:   tail call void @llvm.memcpy.p0i8.p0i8.i64(i8*
> %P, i8* %Q, i64 12, i1 false) <->   tail call void @llvm.assume(i1 true) [
> "nonnull"(i8* %P) ]
> > +; CHECK: NoModRef:   tail call void @llvm.assume(i1 true) [
> "nonnull"(i8* %P) ] <->   tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P,
> i8* %Q, i64 12, i1 false)
> > +; CHECK: NoModRef:   tail call void @llvm.memcpy.p0i8.p0i8.i64(i8* %P,
> i8* %Q, i64 12, i1 false) <->   tail call void @llvm.assume(i1 true) [
> "nonnull"(i8* %P) ]
> >   }
> >
> >   attributes #0 = { nounwind }
> >
> >
> >
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>
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