From 5c6e37cfc139383e87a3a07c325bb4189c84be48 Mon Sep 17 00:00:00 2001 From: Sanjay Patel Date: Mon, 5 Aug 2019 16:04:07 +0000 Subject: [PATCH] [InstCombine] add extra use constraint for shl-zext fold As the test shows, we can end up with more instructions than we started with if we don't include the extra-use check. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@367880 91177308-0d34-0410-b5e6-96231b3b80d8 --- lib/Transforms/InstCombine/InstCombineShifts.cpp | 2 +- test/Transforms/InstCombine/shift.ll | 3 +-- 2 files changed, 2 insertions(+), 3 deletions(-) diff --git a/lib/Transforms/InstCombine/InstCombineShifts.cpp b/lib/Transforms/InstCombine/InstCombineShifts.cpp index 2427d795c47..a30bcbd64ca 100644 --- a/lib/Transforms/InstCombine/InstCombineShifts.cpp +++ b/lib/Transforms/InstCombine/InstCombineShifts.cpp @@ -718,7 +718,7 @@ Instruction *InstCombiner::visitShl(BinaryOperator &I) { // shl (zext X), ShAmt --> zext (shl X, ShAmt) // This is only valid if X would have zeros shifted out. Value *X; - if (match(Op0, m_ZExt(m_Value(X)))) { + if (match(Op0, m_OneUse(m_ZExt(m_Value(X))))) { unsigned SrcWidth = X->getType()->getScalarSizeInBits(); if (ShAmt < SrcWidth && MaskedValueIsZero(X, APInt::getHighBitsSet(SrcWidth, ShAmt), 0, &I)) diff --git a/test/Transforms/InstCombine/shift.ll b/test/Transforms/InstCombine/shift.ll index eaeecacd44d..6bb38da87a8 100644 --- a/test/Transforms/InstCombine/shift.ll +++ b/test/Transforms/InstCombine/shift.ll @@ -1198,8 +1198,7 @@ define i64 @shl_zext_extra_use(i32 %t) { ; CHECK-NEXT: [[AND:%.*]] = and i32 [[T:%.*]], 16777215 ; CHECK-NEXT: [[EXT:%.*]] = zext i32 [[AND]] to i64 ; CHECK-NEXT: call void @use(i64 [[EXT]]) -; CHECK-NEXT: [[TMP1:%.*]] = shl i32 [[T]], 8 -; CHECK-NEXT: [[SHL:%.*]] = zext i32 [[TMP1]] to i64 +; CHECK-NEXT: [[SHL:%.*]] = shl nuw nsw i64 [[EXT]], 8 ; CHECK-NEXT: ret i64 [[SHL]] ; %and = and i32 %t, 16777215 -- 2.40.0