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

[Davide Italiano 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.
>

Also, I think Eli had some questions about your tests, maybe you can
address them as a post-commit review (I don't see the changes here).

-- 
Davide

"There are no solved problems; there are only problems that are more
or less solved" -- Henri Poincare