[llvm] 77aaba6 - [InstCombine] Compute bits of first operand for multi-use sub

[Nikita Popov via llvm-commits]

Author: Nikita Popov
Date: 2023-05-17T18:34:17+02:00
New Revision: 77aaba6aae9667e5091bf35b1cfdef995840a8c9

URL: https://github.com/llvm/llvm-project/commit/77aaba6aae9667e5091bf35b1cfdef995840a8c9
DIFF: https://github.com/llvm/llvm-project/commit/77aaba6aae9667e5091bf35b1cfdef995840a8c9.diff

LOG: [InstCombine] Compute bits of first operand for multi-use sub

Otherwise the result will always be unknown anyway. This fixes one
of the last inconsistencies in results between computeKnownBits()
and SimplifyDemandedBits().

Added: 
    

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

Removed: 
    


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diff  --git a/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
index 5a7ff48efd9c..ac824b275d38 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
@@ -1090,6 +1090,7 @@ Value *InstCombinerImpl::SimplifyMultipleUseDemandedBits(
       return I->getOperand(0);
 
     bool NSW = cast<OverflowingBinaryOperator>(I)->hasNoSignedWrap();
+    computeKnownBits(I->getOperand(0), LHSKnown, Depth + 1, CxtI);
     Known = KnownBits::computeForAddSub(/*Add*/ false, NSW, LHSKnown, RHSKnown);
     break;
   }