[llvm] 12d93a2 - [InstCombine] Sanitize undef vector constant to 1 in X*(2^C) with X << C (PR47133)

[Roman Lebedev via llvm-commits]

Author: Roman Lebedev
Date: 2020-08-12T22:06:53+03:00
New Revision: 12d93a27e7b78d58dd00817cb737f273d2dba8ae

URL: https://github.com/llvm/llvm-project/commit/12d93a27e7b78d58dd00817cb737f273d2dba8ae
DIFF: https://github.com/llvm/llvm-project/commit/12d93a27e7b78d58dd00817cb737f273d2dba8ae.diff

LOG: [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

Added: 
    

Modified: 
    llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
    llvm/test/Transforms/InstCombine/getelementptr.ll
    llvm/test/Transforms/InstCombine/mul.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp b/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
index 89641704a195..6162c546ff10 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
@@ -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())

diff  --git a/llvm/test/Transforms/InstCombine/getelementptr.ll b/llvm/test/Transforms/InstCombine/getelementptr.ll
index 0257725d12de..17362b088241 100644
--- a/llvm/test/Transforms/InstCombine/getelementptr.ll
+++ b/llvm/test/Transforms/InstCombine/getelementptr.ll
@@ -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]]

diff  --git a/llvm/test/Transforms/InstCombine/mul.ll b/llvm/test/Transforms/InstCombine/mul.ll
index 921c80440147..2e9250fe94c4 100644
--- a/llvm/test/Transforms/InstCombine/mul.ll
+++ b/llvm/test/Transforms/InstCombine/mul.ll
@@ -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>