[InstSimplify] Fix addo/subo undef folds (PR42209)

Fix folds of addo and subo with an undef operand to be:

`@llvm.{u,s}{add,sub}.with.overflow` all fold to `{ undef, false }`,
 as per LLVM undef rules.
Same for commuted variants.

Based on the original version of the patch by @nikic.

Fixes [[ https://bugs.llvm.org/show_bug.cgi?id=42209 | PR42209 ]]

Differential Revision: https://reviews.llvm.org/D63065

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@363522 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Analysis/InstructionSimplify.cpp b/lib/Analysis/InstructionSimplify.cpp
index d0b9549..ba76c5b 100644 (file)
--- a/lib/Analysis/InstructionSimplify.cpp
+++ b/lib/Analysis/InstructionSimplify.cpp
@@ -4843,16 +4843,19 @@ static Value *simplifyBinaryIntrinsic(Function *F, Value *Op0, Value *Op1,
     // X - X -> { 0, false }
     if (Op0 == Op1)
       return Constant::getNullValue(ReturnType);
-    // X - undef -> undef
-    // undef - X -> undef
-    if (isa<UndefValue>(Op0) || isa<UndefValue>(Op1))
-      return UndefValue::get(ReturnType);
-    break;
+    LLVM_FALLTHROUGH;
   case Intrinsic::uadd_with_overflow:
   case Intrinsic::sadd_with_overflow:
-    // X + undef -> undef
-    if (isa<UndefValue>(Op0) || isa<UndefValue>(Op1))
-      return UndefValue::get(ReturnType);
+    // X - undef -> { undef, false }
+    // undef - X -> { undef, false }
+    // X + undef -> { undef, false }
+    // undef + x -> { undef, false }
+    if (isa<UndefValue>(Op0) || isa<UndefValue>(Op1)) {
+      return ConstantStruct::get(
+          cast<StructType>(ReturnType),
+          {UndefValue::get(ReturnType->getStructElementType(0)),
+           Constant::getNullValue(ReturnType->getStructElementType(1))});
+    }
     break;
   case Intrinsic::umul_with_overflow:
   case Intrinsic::smul_with_overflow:

diff --git a/test/Transforms/InstCombine/with_overflow.ll b/test/Transforms/InstCombine/with_overflow.ll
index b15e37c..04e8097 100644 (file)
--- a/test/Transforms/InstCombine/with_overflow.ll
+++ b/test/Transforms/InstCombine/with_overflow.ll
@@ -60,6 +60,7 @@ define i8 @uaddtest3(i8 %A, i8 %B, i1* %overflowPtr) {
 
 define i8 @uaddtest4(i8 %A, i1* %overflowPtr) {
 ; CHECK-LABEL: @uaddtest4(
+; CHECK-NEXT:    store i1 false, i1* [[OVERFLOWPTR:%.*]], align 1
 ; CHECK-NEXT:    ret i8 undef
 ;
   %x = call { i8, i1 } @llvm.uadd.with.overflow.i8(i8 undef, i8 %A)

diff --git a/test/Transforms/InstSimplify/call.ll b/test/Transforms/InstSimplify/call.ll
index 0771e44..27497e5 100644 (file)
--- a/test/Transforms/InstSimplify/call.ll
+++ b/test/Transforms/InstSimplify/call.ll
@@ -29,7 +29,7 @@ define i8 @test_uadd2() {
 
 define {i8, i1} @test_uadd3(i8 %v) {
 ; CHECK-LABEL: @test_uadd3(
-; CHECK-NEXT:    ret { i8, i1 } undef
+; CHECK-NEXT:    ret { i8, i1 } { i8 undef, i1 false }
 ;
   %result = call {i8, i1} @llvm.uadd.with.overflow.i8(i8 %v, i8 undef)
   ret {i8, i1} %result
@@ -37,7 +37,7 @@ define {i8, i1} @test_uadd3(i8 %v) {
 
 define {i8, i1} @test_uadd4(i8 %v) {
 ; CHECK-LABEL: @test_uadd4(
-; CHECK-NEXT:    ret { i8, i1 } undef
+; CHECK-NEXT:    ret { i8, i1 } { i8 undef, i1 false }
 ;
   %result = call {i8, i1} @llvm.uadd.with.overflow.i8(i8 undef, i8 %v)
   ret {i8, i1} %result
@@ -63,7 +63,7 @@ define i8 @test_sadd2() {
 
 define {i8, i1} @test_sadd3(i8 %v) {
 ; CHECK-LABEL: @test_sadd3(
-; CHECK-NEXT:    ret { i8, i1 } undef
+; CHECK-NEXT:    ret { i8, i1 } { i8 undef, i1 false }
 ;
   %result = call {i8, i1} @llvm.sadd.with.overflow.i8(i8 %v, i8 undef)
   ret {i8, i1} %result
@@ -71,7 +71,7 @@ define {i8, i1} @test_sadd3(i8 %v) {
 
 define {i8, i1} @test_sadd4(i8 %v) {
 ; CHECK-LABEL: @test_sadd4(
-; CHECK-NEXT:    ret { i8, i1 } undef
+; CHECK-NEXT:    ret { i8, i1 } { i8 undef, i1 false }
 ;
   %result = call {i8, i1} @llvm.sadd.with.overflow.i8(i8 undef, i8 %v)
   ret {i8, i1} %result
@@ -87,7 +87,7 @@ define {i8, i1} @test_usub1(i8 %V) {
 
 define {i8, i1} @test_usub2(i8 %V) {
 ; CHECK-LABEL: @test_usub2(
-; CHECK-NEXT:    ret { i8, i1 } undef
+; CHECK-NEXT:    ret { i8, i1 } { i8 undef, i1 false }
 ;
   %x = call {i8, i1} @llvm.usub.with.overflow.i8(i8 %V, i8 undef)
   ret {i8, i1} %x
@@ -95,7 +95,7 @@ define {i8, i1} @test_usub2(i8 %V) {
 
 define {i8, i1} @test_usub3(i8 %V) {
 ; CHECK-LABEL: @test_usub3(
-; CHECK-NEXT:    ret { i8, i1 } undef
+; CHECK-NEXT:    ret { i8, i1 } { i8 undef, i1 false }
 ;
   %x = call {i8, i1} @llvm.usub.with.overflow.i8(i8 undef, i8 %V)
   ret {i8, i1} %x
@@ -111,7 +111,7 @@ define {i8, i1} @test_ssub1(i8 %V) {
 
 define {i8, i1} @test_ssub2(i8 %V) {
 ; CHECK-LABEL: @test_ssub2(
-; CHECK-NEXT:    ret { i8, i1 } undef
+; CHECK-NEXT:    ret { i8, i1 } { i8 undef, i1 false }
 ;
   %x = call {i8, i1} @llvm.ssub.with.overflow.i8(i8 %V, i8 undef)
   ret {i8, i1} %x
@@ -119,7 +119,7 @@ define {i8, i1} @test_ssub2(i8 %V) {
 
 define {i8, i1} @test_ssub3(i8 %V) {
 ; CHECK-LABEL: @test_ssub3(
-; CHECK-NEXT:    ret { i8, i1 } undef
+; CHECK-NEXT:    ret { i8, i1 } { i8 undef, i1 false }
 ;
   %x = call {i8, i1} @llvm.ssub.with.overflow.i8(i8 undef, i8 %V)
   ret {i8, i1} %x