[llvm] 4c52d51 - [InstCombine] Fix a code-sinking bug after D73832/f1a9efabcb9b

[Fangrui Song via llvm-commits]

Author: Fangrui Song
Date: 2020-03-25T22:50:53-07:00
New Revision: 4c52d51e784ca7603969f2a664e5430d41b9d5dc

URL: https://github.com/llvm/llvm-project/commit/4c52d51e784ca7603969f2a664e5430d41b9d5dc
DIFF: https://github.com/llvm/llvm-project/commit/4c52d51e784ca7603969f2a664e5430d41b9d5dc.diff

LOG: [InstCombine] Fix a code-sinking bug after D73832/f1a9efabcb9b

- UserParent = PN->getIncomingBlock(*I->use_begin());
+ UserParent = PN->getIncomingBlock(*SingleUse);

The first use of I may be droppable (llvm.assume).

When compiling llvm/lib/IR/AutoUpgrade.cpp with a bootstrapped clang
with ThinLTO with minimized bitcode files, I see such a case in
the function _ZN4llvm20UpgradeIntrinsicCallEPNS_8CallInstEPNS_8FunctionE

  clang -c -fthinlto-index=AutoUpgrade.o.thinlto.bc AutoUpgrade.bc -O3

Unfortunately it is really difficult to get a minimized reproduce.

Added: 
    

Modified: 
    llvm/lib/Transforms/InstCombine/InstructionCombining.cpp

Removed: 
    


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diff  --git a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
index b62f19eeed64..f2bc6968c3e8 100644
--- a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -3505,7 +3505,7 @@ bool InstCombiner::run() {
 
         // Get the block the use occurs in.
         if (PHINode *PN = dyn_cast<PHINode>(UserInst))
-          UserParent = PN->getIncomingBlock(*I->use_begin());
+          UserParent = PN->getIncomingBlock(*SingleUse);
         else
           UserParent = UserInst->getParent();