[Diffusion] rL277877: [LoopSimplify] Fix updating LCSSA after separating nested loops.

[Michael Zolotukhin via llvm-commits]

> On Aug 8, 2016, at 9:55 AM, Hans Wennborg <hans at chromium.org> wrote:
> 
> Can a regular user run into this? The PR talks about the new pass
> manager. I haven't followed along very well, is that (partially)
> enabled by default these days?
It can also be exposed with the old PM (I mentioned a way in the comments to that bug). It was just discovered with the new PM.
> 
> From the PR it also sounds like the original test case still fails?
I’ll look into it, probably there is more than one issue there. It still might be a good idea to merge this in, as the test from the commit would fail without the fix anyway.

Thanks,
Michael

> Thanks,
> Hans
> 
> On Fri, Aug 5, 2016 at 3:12 PM, Michael Zolotukhin
> <mzolotukhin at apple.com> wrote:
>> Hi Hans,
>> 
>> I think this fix is worth merging to the branch.
>> 
>> Thanks,
>> Michael
>> 
>>> On Aug 5, 2016, at 3:00 PM, Michael Zolotukhin <mzolotukhin at apple.com> wrote:
>>> 
>>> mzolotukhin committed rL277877: [LoopSimplify] Fix updating LCSSA after separating nested loops..
>>> 
>>> [LoopSimplify] Fix updating LCSSA after separating nested loops.
>>> 
>>> This fixes PR28825. The problem was that we only checked if a value from
>>> a created inner loop is used in the outer loop, and fixed LCSSA for
>>> them. But we missed to fixup LCSSA for values used in exits of the outer
>>> loop.
>>> 
>>> 
>>> Files:
>>> /llvm/trunk/lib/Transforms/Utils/LoopSimplify.cpp
>>> /llvm/trunk/test/Transforms/LoopSimplify/pr28272.ll
>>> 
>>> PATCH
>>> 
>>> Index: llvm/trunk/lib/Transforms/Utils/LoopSimplify.cpp
>>> ===================================================================
>>> --- llvm/trunk/lib/Transforms/Utils/LoopSimplify.cpp  (revision 277876)
>>> +++ llvm/trunk/lib/Transforms/Utils/LoopSimplify.cpp  (revision 277877)
>>> @@ -376,6 +376,21 @@
>>>        }
>>>      }
>>>    }
>>> +    // We also need to check exit blocks of the outer loop - it might be using
>>> +    // values from what now became an inner loop.
>>> +    SmallVector<BasicBlock*, 8> ExitBlocks;
>>> +    NewOuter->getExitBlocks(ExitBlocks);
>>> +    for (BasicBlock *ExitBB: ExitBlocks) {
>>> +      for (Instruction &I : *ExitBB) {
>>> +        for (Value *Op : I.operands()) {
>>> +          Instruction *OpI = dyn_cast<Instruction>(Op);
>>> +          if (!OpI || !L->contains(OpI))
>>> +            continue;
>>> +          WorklistSet.insert(OpI);
>>> +        }
>>> +      }
>>> +    }
>>> +
>>>    SmallVector<Instruction *, 8> Worklist(WorklistSet.begin(),
>>>                                           WorklistSet.end());
>>>    formLCSSAForInstructions(Worklist, *DT, *LI);
>>> Index: llvm/trunk/test/Transforms/LoopSimplify/pr28272.ll
>>> ===================================================================
>>> --- llvm/trunk/test/Transforms/LoopSimplify/pr28272.ll        (revision 277876)
>>> +++ llvm/trunk/test/Transforms/LoopSimplify/pr28272.ll        (revision 277877)
>>> @@ -1,7 +1,7 @@
>>> ; RUN: opt < %s -lcssa -loop-unroll -S | FileCheck %s
>>> target triple = "x86_64-unknown-linux-gnu"
>>> 
>>> -; PR28272
>>> +; PR28272, PR28825
>>> ; When LoopSimplify separates nested loops, it might break LCSSA form: values
>>> ; from the original loop might be used in the outer loop. This test invokes
>>> ; loop-unroll, which calls loop-simplify before itself. If LCSSA is broken
>>> @@ -74,3 +74,35 @@
>>> bb:
>>>  br label %loop2
>>> }
>>> +
>>> +; When LoopSimplify separates nested loops, it might break LCSSA form: values
>>> +; from the original loop might be used in exit blocks of the outer loop.
>>> +; CHECK-LABEL: @foo3
>>> +define void @foo3() {
>>> +entry:
>>> +  br label %bb1
>>> +
>>> +bb1:
>>> +  br i1 undef, label %bb2, label %bb1
>>> +
>>> +bb2:
>>> +  %a = phi i32 [ undef, %bb1 ], [ %a, %bb3 ], [ undef, %bb5 ]
>>> +  br i1 undef, label %bb3, label %bb1
>>> +
>>> +bb3:
>>> +  %b = load i32*, i32** undef
>>> +  br i1 undef, label %bb2, label %bb4
>>> +
>>> +bb4:
>>> +  br i1 undef, label %bb5, label %bb6
>>> +
>>> +bb5:
>>> +  br i1 undef, label %bb2, label %bb4
>>> +
>>> +bb6:
>>> +  br i1 undef, label %bb_end, label %bb1
>>> +
>>> +bb_end:
>>> +  %x = getelementptr i32, i32* %b
>>> +  br label %bb_end
>>> +}
>>> 
>>> Users:
>>> mzolotukhin (Author)
>>> 
>>> https://reviews.llvm.org/rL277877
>>> 
>>> 
>>> 
>>