[llvm] r272703 - [ValueTracking] Calls to @llvm.assume always return

[David Majnemer via llvm-commits]

Hmm, what if we have:

volatile store i32 0, i32* %p
call void @llvm.assume(i1 false)
...

Can't this sort of logic let us sink the store past the assume? What if the
assume gets replaced with unreachable?


On Tue, Jun 14, 2016 at 1:33 PM, Sanjoy Das via llvm-commits <
llvm-commits at lists.llvm.org> wrote:

> Forgot to mention in the commit message: this regression was
> introduced in http://reviews.llvm.org/rL272489
>
> On Tue, Jun 14, 2016 at 1:23 PM, Sanjoy Das via llvm-commits
> <llvm-commits at lists.llvm.org> wrote:
> > Author: sanjoy
> > Date: Tue Jun 14 15:23:16 2016
> > New Revision: 272703
> >
> > URL: http://llvm.org/viewvc/llvm-project?rev=272703&view=rev
> > Log:
> > [ValueTracking] Calls to @llvm.assume always return
> >
> > This change teaches llvm::isGuaranteedToTransferExecutionToSuccessor
> > that calls to @llvm.assume always terminate.  Most other relevant
> > intrinsics should be covered by the "CS.onlyReadsMemory() ||
> > CS.onlyAccessesArgMemory()" bit but we were missing @llvm.assumes
> > because we state that it clobbers memory.
> >
> > Added an LICM test case, but this change is not specific to LICM.
> >
> > Modified:
> >     llvm/trunk/lib/Analysis/ValueTracking.cpp
> >     llvm/trunk/test/Transforms/LICM/assume.ll
> >
> > Modified: llvm/trunk/lib/Analysis/ValueTracking.cpp
> > URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/ValueTracking.cpp?rev=272703&r1=272702&r2=272703&view=diff
> >
> ==============================================================================
> > --- llvm/trunk/lib/Analysis/ValueTracking.cpp (original)
> > +++ llvm/trunk/lib/Analysis/ValueTracking.cpp Tue Jun 14 15:23:16 2016
> > @@ -3478,7 +3478,8 @@ bool llvm::isGuaranteedToTransferExecuti
> >      // but it's consistent with other passes. See http://llvm.org/PR965
> .
> >      // FIXME: This isn't aggressive enough; a call which only writes to
> a
> >      // global is guaranteed to return.
> > -    return CS.onlyReadsMemory() || CS.onlyAccessesArgMemory();
> > +    return CS.onlyReadsMemory() || CS.onlyAccessesArgMemory() ||
> > +           match(I, m_Intrinsic<Intrinsic::assume>());
> >    }
> >
> >    // Other instructions return normally.
> >
> > Modified: llvm/trunk/test/Transforms/LICM/assume.ll
> > URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/LICM/assume.ll?rev=272703&r1=272702&r2=272703&view=diff
> >
> ==============================================================================
> > --- llvm/trunk/test/Transforms/LICM/assume.ll (original)
> > +++ llvm/trunk/test/Transforms/LICM/assume.ll Tue Jun 14 15:23:16 2016
> > @@ -1,6 +1,7 @@
> >  ; RUN: opt -licm -basicaa < %s -S | FileCheck %s
> >
> > -define void @f(i1 %p) nounwind ssp {
> > +define void @f_0(i1 %p) nounwind ssp {
> > +; CHECK-LABEL: @f_0(
> >  entry:
> >    br label %for.body
> >
> > @@ -31,4 +32,20 @@ for.end104:
> >    ret void
> >  }
> >
> > +define void @f_1(i1 %cond, i32* %ptr) {
> > +; CHECK-LABEL: @f_1(
> > +; CHECK: %val = load i32, i32* %ptr
> > +; CHECK-NEXT:  br label %loop
> > +
> > +entry:
> > +  br label %loop
> > +
> > +loop:
> > +  %x = phi i32 [ 0, %entry ], [ %x.inc, %loop ]
> > +  call void @llvm.assume(i1 %cond)
> > +  %val = load i32, i32* %ptr
> > +  %x.inc = add i32 %x, %val
> > +  br label %loop
> > +}
> > +
> >  declare void @llvm.assume(i1)
> >
> >
> > _______________________________________________
> > llvm-commits mailing list
> > llvm-commits at lists.llvm.org
> > http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-commits
>
>
>
> --
> Sanjoy Das
> http://playingwithpointers.com
> _______________________________________________
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> llvm-commits at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-commits
>
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