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[InstCombine] add extra use constraint for shl-zext fold

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As the test shows, we can end up with more instructions than
we started with if we don't include the extra-use check.

llvm-svn: 367880
This commit is contained in:
Sanjay Patel 2019-08-05 16:04:07 +00:00
parent 2028ac72f0
commit 3671d23fc9
2 changed files with 2 additions and 3 deletions
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2
lib/Transforms/InstCombine/InstCombineShifts.cpp
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@ -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))

3
test/Transforms/InstCombine/shift.ll
View File

@ -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