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

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
This commit is contained in:
Roman Lebedev 2020-08-12 21:06:28 +03:00
parent c561f4d2ec
commit 12d93a27e7
No known key found for this signature in database
GPG Key ID: 083C3EBB4A1689E0
3 changed files with 10 additions and 6 deletions
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6
llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
View File

@ -217,7 +217,11 @@ Instruction *InstCombinerImpl::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
llvm/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]]

6
llvm/test/Transforms/InstCombine/mul.ll
View File

@ -908,7 +908,7 @@ define <2 x i32> @mulsub1_vec_nonuniform(<2 x i32> %a0, <2 x i32> %a1) {
define <2 x i32> @mulsub1_vec_nonuniform_undef(<2 x i32> %a0, <2 x i32> %a1) {
; CHECK-LABEL: @mulsub1_vec_nonuniform_undef(
; CHECK-NEXT: [[SUB_NEG:%.*]] = sub <2 x i32> [[A0:%.*]], [[A1:%.*]]
; CHECK-NEXT: [[MUL:%.*]] = shl <2 x i32> [[SUB_NEG]], <i32 2, i32 undef>
; CHECK-NEXT: [[MUL:%.*]] = shl <2 x i32> [[SUB_NEG]], <i32 2, i32 0>
; CHECK-NEXT: ret <2 x i32> [[MUL]]
;
%sub = sub <2 x i32> %a1, %a0
@ -952,7 +952,7 @@ define <2 x i32> @mulsub2_vec_nonuniform(<2 x i32> %a0) {
define <2 x i32> @mulsub2_vec_nonuniform_undef(<2 x i32> %a0) {
; CHECK-LABEL: @mulsub2_vec_nonuniform_undef(
; CHECK-NEXT: [[SUB_NEG:%.*]] = add <2 x i32> [[A0:%.*]], <i32 -16, i32 -32>
; CHECK-NEXT: [[MUL:%.*]] = shl <2 x i32> [[SUB_NEG]], <i32 2, i32 undef>
; CHECK-NEXT: [[MUL:%.*]] = shl <2 x i32> [[SUB_NEG]], <i32 2, i32 0>
; CHECK-NEXT: ret <2 x i32> [[MUL]]
;
%sub = sub <2 x i32> <i32 16, i32 32>, %a0
@ -996,7 +996,7 @@ define <2 x i32> @muladd2_vec_nonuniform(<2 x i32> %a0) {
define <2 x i32> @muladd2_vec_nonuniform_undef(<2 x i32> %a0) {
; CHECK-LABEL: @muladd2_vec_nonuniform_undef(
; CHECK-NEXT: [[ADD_NEG:%.*]] = sub <2 x i32> <i32 -16, i32 -32>, [[A0:%.*]]
; CHECK-NEXT: [[MUL:%.*]] = shl <2 x i32> [[ADD_NEG]], <i32 2, i32 undef>
; CHECK-NEXT: [[MUL:%.*]] = shl <2 x i32> [[ADD_NEG]], <i32 2, i32 0>
; CHECK-NEXT: ret <2 x i32> [[MUL]]
;
%add = add <2 x i32> %a0, <i32 16, i32 32>