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[InstCombine] Sanitize undef vector constant to 1 in X*(2^C) with X << C (PR47133)

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While x*undef is undef, shift-by-undef is poison,
which we must avoid introducing.

Also log2(iN undef) is *NOT* iN undef, because log2(iN undef) u< N.

See https://bugs.llvm.org/show_bug.cgi?id=47133

(cherry picked from commit 12d93a27e7b78d58dd00817cb737f273d2dba8ae)
This commit is contained in:
Roman Lebedev 2020-08-12 21:06:28 +03:00 committed by Hans Wennborg
parent f0d66a02ba
commit 7b99daf6d1
2 changed files with 7 additions and 3 deletions
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6
lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
View File

@ -216,7 +216,11 @@ Instruction *InstCombiner::visitMul(BinaryOperator &I) {
if (match(&I, m_Mul(m_Value(NewOp), m_Constant(C1)))) {
// Replace X*(2^C) with X << C, where C is either a scalar or a vector.
if (Constant *NewCst = getLogBase2(NewOp->getType(), C1)) {
// Note that we need to sanitize undef multipliers to 1,
// to avoid introducing poison.
Constant *SafeC1 = Constant::replaceUndefsWith(
C1, ConstantInt::get(C1->getType()->getScalarType(), 1));
if (Constant *NewCst = getLogBase2(NewOp->getType(), SafeC1)) {
BinaryOperator *Shl = BinaryOperator::CreateShl(NewOp, NewCst);
if (I.hasNoUnsignedWrap())

4
test/Transforms/InstCombine/getelementptr.ll
View File

@ -216,7 +216,7 @@ define <2 x i1> @test13_vector(<2 x i64> %X, <2 x %S*> %P) nounwind {
define <2 x i1> @test13_vector2(i64 %X, <2 x %S*> %P) nounwind {
; CHECK-LABEL: @test13_vector2(
; CHECK-NEXT: [[DOTSPLATINSERT:%.*]] = insertelement <2 x i64> undef, i64 [[X:%.*]], i32 0
; CHECK-NEXT: [[TMP1:%.*]] = shl <2 x i64> [[DOTSPLATINSERT]], <i64 2, i64 undef>
; CHECK-NEXT: [[TMP1:%.*]] = shl <2 x i64> [[DOTSPLATINSERT]], <i64 2, i64 0>
; CHECK-NEXT: [[TMP2:%.*]] = icmp eq <2 x i64> [[TMP1]], <i64 -4, i64 undef>
; CHECK-NEXT: [[C:%.*]] = shufflevector <2 x i1> [[TMP2]], <2 x i1> undef, <2 x i32> zeroinitializer
; CHECK-NEXT: ret <2 x i1> [[C]]
@ -231,7 +231,7 @@ define <2 x i1> @test13_vector2(i64 %X, <2 x %S*> %P) nounwind {
define <2 x i1> @test13_vector3(i64 %X, <2 x %S*> %P) nounwind {
; CHECK-LABEL: @test13_vector3(
; CHECK-NEXT: [[DOTSPLATINSERT:%.*]] = insertelement <2 x i64> undef, i64 [[X:%.*]], i32 0
; CHECK-NEXT: [[TMP1:%.*]] = shl <2 x i64> [[DOTSPLATINSERT]], <i64 2, i64 undef>
; CHECK-NEXT: [[TMP1:%.*]] = shl <2 x i64> [[DOTSPLATINSERT]], <i64 2, i64 0>
; CHECK-NEXT: [[TMP2:%.*]] = icmp eq <2 x i64> [[TMP1]], <i64 4, i64 undef>
; CHECK-NEXT: [[C:%.*]] = shufflevector <2 x i1> [[TMP2]], <2 x i1> undef, <2 x i32> zeroinitializer
; CHECK-NEXT: ret <2 x i1> [[C]]