[llvm] r294632 - [LoadCombine] Fix combining of loads which span an aliasing store.

[Michael Spencer via llvm-commits]

On Thu, Feb 9, 2017 at 2:01 PM, Davide Italiano <davide at freebsd.org> wrote:

> On Thu, Feb 9, 2017 at 1:46 PM, Michael J. Spencer via llvm-commits
> <llvm-commits at lists.llvm.org> wrote:
> > Author: mspencer
> > Date: Thu Feb  9 15:46:49 2017
> > New Revision: 294632
> >
> > URL: http://llvm.org/viewvc/llvm-project?rev=294632&view=rev
> > Log:
> > [LoadCombine] Fix combining of loads which span an aliasing store.
> >
> > Fixes PR31517
> >
> > Differential Revision: https://reviews.llvm.org/D28922
> >
> > Modified:
> >     llvm/trunk/lib/Transforms/Scalar/LoadCombine.cpp
> >     llvm/trunk/test/Transforms/LoadCombine/load-combine-aa.ll
> >
> > Modified: llvm/trunk/lib/Transforms/Scalar/LoadCombine.cpp
> > URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/
> Transforms/Scalar/LoadCombine.cpp?rev=294632&r1=294631&r2=294632&view=diff
> > ============================================================
> ==================
> > --- llvm/trunk/lib/Transforms/Scalar/LoadCombine.cpp (original)
> > +++ llvm/trunk/lib/Transforms/Scalar/LoadCombine.cpp Thu Feb  9
> 15:46:49 2017
> > @@ -245,13 +245,17 @@ bool LoadCombine::runOnBasicBlock(BasicB
> >    bool Combined = false;
> >    unsigned Index = 0;
> >    for (auto &I : BB) {
> > -    if (I.mayThrow() || (I.mayWriteToMemory() &&
> AST.containsUnknown(&I))) {
> > +    if (I.mayThrow() || AST.containsUnknown(&I)) {
> >        if (combineLoads(LoadMap))
> >          Combined = true;
> >        LoadMap.clear();
> >        AST.clear();
> >        continue;
> >      }
> > +    if (I.mayWriteToMemory()) {
> > +      AST.add(&I);
> > +      continue;
> > +    }
> >      LoadInst *LI = dyn_cast<LoadInst>(&I);
> >      if (!LI)
> >        continue;
> >
> > Modified: llvm/trunk/test/Transforms/LoadCombine/load-combine-aa.ll
> > URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/
> Transforms/LoadCombine/load-combine-aa.ll?rev=294632&r1=
> 294631&r2=294632&view=diff
> > ============================================================
> ==================
> > --- llvm/trunk/test/Transforms/LoadCombine/load-combine-aa.ll (original)
> > +++ llvm/trunk/test/Transforms/LoadCombine/load-combine-aa.ll Thu Feb
> 9 15:46:49 2017
> > @@ -37,3 +37,24 @@ define i64 @test2(i32* nocapture readonl
> >    ret i64 %add
> >  }
> >
> > +%rec11 = type { i16, i16, i16 }
> > + at str = global %rec11 { i16 1, i16 2, i16 3 }
> > +
> > +; PR31517 - Check that loads which span an aliasing store are not
> combined.
> > +define i16 @test3() {
> > +; CHECK-LABEL: @test3
> > +
> > +; CHECK: load i16, i16*
> > +; CHECK: store i16
> > +; CHECK: ret i16
> > +
> > +  %_tmp9 = getelementptr %rec11, %rec11* @str, i16 0, i32 1
> > +  %_tmp10 = load i16, i16* %_tmp9
> > +  %_tmp12 = getelementptr %rec11, %rec11* @str, i16 0, i32 0
> > +  store i16 %_tmp10, i16* %_tmp12
> > +  %_tmp13 = getelementptr %rec11, %rec11* @str, i16 0, i32 0
> > +  %_tmp14 = load i16, i16* %_tmp13
> > +  %_tmp15 = icmp eq i16 %_tmp14, 3
> > +  %_tmp16 = select i1 %_tmp15, i16 1, i16 0
> > +  ret i16 %_tmp16
> > +}
> >
> >
>
> I think it's a good idea to change this tests to not rely on
> instcombine anymore.


The IR gets pretty ugly if you do that and makes the test harder to
understand.

- Michael Spencer
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