[InstCombine] foldICmpWithLowBitMaskedVal(): don't miscompile -1 vector elts

I was finally able to quantify what i thought was missing in the fix,
it was vector constants. If we have a scalar (and %x, -1),
it will be instsimplified before we reach this code,
but if it is a vector, we may still have a -1 element.

Thus, we want to avoid the fold if *at least one* element is -1.
Or in other words, ignoring the undef elements, no sign bits
should be set. Thus, m_NonNegative().

A follow-up for rL348181
https://bugs.llvm.org/show_bug.cgi?id=39861

llvm-svn: 348462

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
index 8dbf5aa..41a1a28 100644 (file)
--- a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -2974,6 +2974,8 @@ static Value *foldICmpWithLowBitMaskedVal(ICmpInst &I,
       return nullptr;         // Ignore the other case.
     if (!match(M, m_Constant())) // Can not do this fold with non-constant.
       return nullptr;
+    if (!match(M, m_NonNegative())) // Must not have any -1 vector elements.
+      return nullptr;
     DstPred = ICmpInst::Predicate::ICMP_SLE;
     break;
   case ICmpInst::Predicate::ICMP_SLT:
@@ -2982,6 +2984,8 @@ static Value *foldICmpWithLowBitMaskedVal(ICmpInst &I,
       return nullptr;         // Ignore the other case.
     if (!match(M, m_Constant())) // Can not do this fold with non-constant.
       return nullptr;
+    if (!match(M, m_NonNegative())) // Must not have any -1 vector elements.
+      return nullptr;
     DstPred = ICmpInst::Predicate::ICMP_SGT;
     break;
   case ICmpInst::Predicate::ICMP_SLE:

diff --git a/llvm/test/Transforms/InstCombine/canonicalize-constant-low-bit-mask-and-icmp-sge-to-icmp-sle.ll b/llvm/test/Transforms/InstCombine/canonicalize-constant-low-bit-mask-and-icmp-sge-to-icmp-sle.ll
index 36994b3..ca1b86c 100644 (file)
--- a/llvm/test/Transforms/InstCombine/canonicalize-constant-low-bit-mask-and-icmp-sge-to-icmp-sle.ll
+++ b/llvm/test/Transforms/InstCombine/canonicalize-constant-low-bit-mask-and-icmp-sge-to-icmp-sle.ll
@@ -205,8 +205,9 @@ define i1 @nv(i8 %x, i8 %y) {
 
 define <2 x i1> @n3_vec(<2 x i8> %x) {
 ; CHECK-LABEL: @n3_vec(
-; CHECK-NEXT:    [[TMP1:%.*]] = icmp slt <2 x i8> [[X:%.*]], <i8 4, i8 0>
-; CHECK-NEXT:    ret <2 x i1> [[TMP1]]
+; CHECK-NEXT:    [[TMP0:%.*]] = and <2 x i8> [[X:%.*]], <i8 3, i8 -1>
+; CHECK-NEXT:    [[RET:%.*]] = icmp sge <2 x i8> [[TMP0]], [[X]]
+; CHECK-NEXT:    ret <2 x i1> [[RET]]
 ;
   %tmp0 = and <2 x i8> %x, <i8 3, i8 -1>
   %ret = icmp sge <2 x i8> %tmp0, %x
@@ -215,8 +216,9 @@ define <2 x i1> @n3_vec(<2 x i8> %x) {
 
 define <3 x i1> @n4_vec(<3 x i8> %x) {
 ; CHECK-LABEL: @n4_vec(
-; CHECK-NEXT:    [[TMP1:%.*]] = icmp slt <3 x i8> [[X:%.*]], <i8 4, i8 undef, i8 0>
-; CHECK-NEXT:    ret <3 x i1> [[TMP1]]
+; CHECK-NEXT:    [[TMP0:%.*]] = and <3 x i8> [[X:%.*]], <i8 3, i8 undef, i8 -1>
+; CHECK-NEXT:    [[RET:%.*]] = icmp sge <3 x i8> [[TMP0]], [[X]]
+; CHECK-NEXT:    ret <3 x i1> [[RET]]
 ;
   %tmp0 = and <3 x i8> %x, <i8 3, i8 undef, i8 -1>
   %ret = icmp sge <3 x i8> %tmp0, %x

diff --git a/llvm/test/Transforms/InstCombine/canonicalize-constant-low-bit-mask-and-icmp-slt-to-icmp-sgt.ll b/llvm/test/Transforms/InstCombine/canonicalize-constant-low-bit-mask-and-icmp-slt-to-icmp-sgt.ll
index 281f9e8..2957ad5 100644 (file)
--- a/llvm/test/Transforms/InstCombine/canonicalize-constant-low-bit-mask-and-icmp-slt-to-icmp-sgt.ll
+++ b/llvm/test/Transforms/InstCombine/canonicalize-constant-low-bit-mask-and-icmp-slt-to-icmp-sgt.ll
@@ -205,8 +205,9 @@ define i1 @nv(i8 %x, i8 %y) {
 
 define <2 x i1> @n3(<2 x i8> %x) {
 ; CHECK-LABEL: @n3(
-; CHECK-NEXT:    [[TMP1:%.*]] = icmp sgt <2 x i8> [[X:%.*]], <i8 3, i8 -1>
-; CHECK-NEXT:    ret <2 x i1> [[TMP1]]
+; CHECK-NEXT:    [[TMP0:%.*]] = and <2 x i8> [[X:%.*]], <i8 3, i8 -1>
+; CHECK-NEXT:    [[RET:%.*]] = icmp slt <2 x i8> [[TMP0]], [[X]]
+; CHECK-NEXT:    ret <2 x i1> [[RET]]
 ;
   %tmp0 = and <2 x i8> %x, <i8 3, i8 -1>
   %ret = icmp slt <2 x i8> %tmp0, %x
@@ -215,8 +216,9 @@ define <2 x i1> @n3(<2 x i8> %x) {
 
 define <3 x i1> @n4(<3 x i8> %x) {
 ; CHECK-LABEL: @n4(
-; CHECK-NEXT:    [[TMP1:%.*]] = icmp sgt <3 x i8> [[X:%.*]], <i8 3, i8 undef, i8 -1>
-; CHECK-NEXT:    ret <3 x i1> [[TMP1]]
+; CHECK-NEXT:    [[TMP0:%.*]] = and <3 x i8> [[X:%.*]], <i8 3, i8 undef, i8 -1>
+; CHECK-NEXT:    [[RET:%.*]] = icmp slt <3 x i8> [[TMP0]], [[X]]
+; CHECK-NEXT:    ret <3 x i1> [[RET]]
 ;
   %tmp0 = and <3 x i8> %x, <i8 3, i8 undef, i8 -1>
   %ret = icmp slt <3 x i8> %tmp0, %x