[PATCH] D25135: [InstCombine] sub X, sext(bool Y) -> add X, zext(bool Y)

[Eli Friedman via llvm-commits]

efriedma added inline comments.


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Comment at: lib/Transforms/InstCombine/InstCombineAddSub.cpp:1648
+    // But ignore a 'sub nuw' because we can't transfer nuw to the add. 
+    if (!I.hasNoUnsignedWrap() && match(Op1, m_SExt(m_Value(Y))) &&
+        Y->getType()->getScalarSizeInBits() == 1) {
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I would favor dropping the nuw flag over keeping IR in a form that isn't canonical.


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Comment at: test/Transforms/InstCombine/urem.ll:32
+; CHECK-NEXT:    [[TMP1:%.*]] = zext i1 [[NOT_]] to i5
+; CHECK-NEXT:    [[REM:%.*]] = add i5 [[TMP1]], %x
 ; CHECK-NEXT:    ret i5 [[REM]]
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For example, this seems better than "sub nuw i5 %x, %tmp".


https://reviews.llvm.org/D25135