llvm dev - Aug 2016 - [MemorySSA] bug in MemorySSA construction

There appears to be a bug in MemorySSA that sometimes results in memory 
defs that don't dominate their uses.  If you apply the below patch and 
run the following command you should be able to reproduce the issue.  I 
haven't been able to investigate it yet, but may do so tomorrow if no 
one gets to it first.


$ opt -print-memoryssa 
llvm/test/Transforms/GlobalDCE/complex-constantexpr.ll

diff --git a/lib/Transforms/Utils/MemorySSA.cpp 
b/lib/Transforms/Utils/MemorySSA.cpp
index 4a604c9..ed2574b 100644
--- a/lib/Transforms/Utils/MemorySSA.cpp
+++ b/lib/Transforms/Utils/MemorySSA.cpp
@@ -1900,7 +1900,9 @@ void MemorySSA::verifyDomination(Function &F) const {
              }
            }
          } else {
-          UseBlock = cast<MemoryAccess>(U)->getBlock();
+          auto *MA = cast<MemoryAccess>(U);
+          UseBlock = MA->getBlock();
+          assert(MD->getBlock() != UseBlock || locallyDominates(MD, MA));
          }
          assert(DT->dominates(MD->getBlock(), UseBlock) &&
                 "Memory Def does not dominate it's uses");

-- 
Geoff Berry
Employee of Qualcomm Innovation Center, Inc.
  Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux
Foundation Collaborative Project

The problem is that we somehow end up trying to optimize the same block 3
times ....
Inorder Dominator Tree:
  [1] %bb {0,9}
    [2] %bb2 {1,8}
      [3] %bb11 {2,7}
        [4] %bb1 {3,4}
        [4] %bb15 {5,6}

Use Optimizer visiting block bb
Use Optimizer visiting block bb2
Use Optimizer visiting block bb11
Use Optimizer visiting block bb1
Use Optimizer visiting block bb11
Use Optimizer visiting block bb15
Use Optimizer visiting block bb11
Use Optimizer visiting block bb2
Use Optimizer visiting block bb


I see what is wrong with the iterator, but i'm just going to replace it
with depth_first anyway.



On Thu, Aug 4, 2016 at 2:35 PM, Geoff Berry <gberry at codeaurora.org>
wrote:
> There appears to be a bug in MemorySSA that sometimes results in memory
> defs that don't dominate their uses.  If you apply the below patch and
run
> the following command you should be able to reproduce the issue.  I
haven't
> been able to investigate it yet, but may do so tomorrow if no one gets to
> it first.
>
>
> $ opt -print-memoryssa llvm/test/Transforms/GlobalDCE
> /complex-constantexpr.ll
>
> diff --git a/lib/Transforms/Utils/MemorySSA.cpp
> b/lib/Transforms/Utils/MemorySSA.cpp
> index 4a604c9..ed2574b 100644
> --- a/lib/Transforms/Utils/MemorySSA.cpp
> +++ b/lib/Transforms/Utils/MemorySSA.cpp
> @@ -1900,7 +1900,9 @@ void MemorySSA::verifyDomination(Function &F)
const
> {
>              }
>            }
>          } else {
> -          UseBlock = cast<MemoryAccess>(U)->getBlock();
> +          auto *MA = cast<MemoryAccess>(U);
> +          UseBlock = MA->getBlock();
> +          assert(MD->getBlock() != UseBlock || locallyDominates(MD,
MA));
>          }
>          assert(DT->dominates(MD->getBlock(), UseBlock) &&
>                 "Memory Def does not dominate it's uses");
>
> --
> Geoff Berry
> Employee of Qualcomm Innovation Center, Inc.
>  Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a
> Linux Foundation Collaborative Project
>
>
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