From 77e07cc0109b5f6b7feb7dc72eda01f656b164af Mon Sep 17 00:00:00 2001
From: Craig Topper <craig.topper@gmail.com>
Date: Wed, 24 May 2017 17:05:28 +0000
Subject: [PATCH] [InstSimplify] Simplify uadd/sadd/umul/smul with overflow
 intrinsics when the Zero or Undef is on the LHS.

Summary: This code was migrated from InstCombine a few years ago. InstCombine had nearby code that would move Constants to the RHS for these, but InstSimplify doesn't have such code on this path.

Reviewers: spatel, majnemer, davide

Reviewed By: spatel

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D33473

llvm-svn: 303774
---
 llvm/lib/Analysis/InstructionSimplify.cpp |  8 ++--
 llvm/test/Transforms/InstSimplify/call.ll | 48 +++++++++++++++++++++++
 2 files changed, 53 insertions(+), 3 deletions(-)

diff --git a/llvm/lib/Analysis/InstructionSimplify.cpp b/llvm/lib/Analysis/InstructionSimplify.cpp
index 9572d81e471b..f10e2378fdbb 100644
--- a/llvm/lib/Analysis/InstructionSimplify.cpp
+++ b/llvm/lib/Analysis/InstructionSimplify.cpp
@@ -4440,19 +4440,21 @@ static Value *SimplifyIntrinsic(Function *F, IterTy ArgBegin, IterTy ArgEnd,
     case Intrinsic::uadd_with_overflow:
     case Intrinsic::sadd_with_overflow: {
       // X + undef -> undef
-      if (isa<UndefValue>(RHS))
+      if (isa<UndefValue>(LHS) || isa<UndefValue>(RHS))
         return UndefValue::get(ReturnType);
 
       return nullptr;
     }
     case Intrinsic::umul_with_overflow:
     case Intrinsic::smul_with_overflow: {
+      // 0 * X -> { 0, false }
       // X * 0 -> { 0, false }
-      if (match(RHS, m_Zero()))
+      if (match(LHS, m_Zero()) || match(RHS, m_Zero()))
         return Constant::getNullValue(ReturnType);
 
+      // undef * X -> { 0, false }
       // X * undef -> { 0, false }
-      if (match(RHS, m_Undef()))
+      if (match(LHS, m_Undef()) || match(RHS, m_Undef()))
         return Constant::getNullValue(ReturnType);
 
       return nullptr;
diff --git a/llvm/test/Transforms/InstSimplify/call.ll b/llvm/test/Transforms/InstSimplify/call.ll
index 5d68fbea436c..68daac65ee6b 100644
--- a/llvm/test/Transforms/InstSimplify/call.ll
+++ b/llvm/test/Transforms/InstSimplify/call.ll
@@ -35,6 +35,14 @@ define {i8, i1} @test_uadd3(i8 %v) {
   ret {i8, i1} %result
 }
 
+define {i8, i1} @test_uadd4(i8 %v) {
+; CHECK-LABEL: @test_uadd4(
+; CHECK-NEXT:    ret { i8, i1 } undef
+;
+  %result = call {i8, i1} @llvm.uadd.with.overflow.i8(i8 undef, i8 %v)
+  ret {i8, i1} %result
+}
+
 define i1 @test_sadd1() {
 ; CHECK-LABEL: @test_sadd1(
 ; CHECK-NEXT:    ret i1 true
@@ -61,6 +69,14 @@ define {i8, i1} @test_sadd3(i8 %v) {
   ret {i8, i1} %result
 }
 
+define {i8, i1} @test_sadd4(i8 %v) {
+; CHECK-LABEL: @test_sadd4(
+; CHECK-NEXT:    ret { i8, i1 } undef
+;
+  %result = call {i8, i1} @llvm.sadd.with.overflow.i8(i8 undef, i8 %v)
+  ret {i8, i1} %result
+}
+
 define {i8, i1} @test_usub1(i8 %V) {
 ; CHECK-LABEL: @test_usub1(
 ; CHECK-NEXT:    ret { i8, i1 } zeroinitializer
@@ -125,6 +141,22 @@ define {i8, i1} @test_umul2(i8 %V) {
   ret {i8, i1} %x
 }
 
+define {i8, i1} @test_umul3(i8 %V) {
+; CHECK-LABEL: @test_umul3(
+; CHECK-NEXT:    ret { i8, i1 } zeroinitializer
+;
+  %x = call {i8, i1} @llvm.umul.with.overflow.i8(i8 0, i8 %V)
+  ret {i8, i1} %x
+}
+
+define {i8, i1} @test_umul4(i8 %V) {
+; CHECK-LABEL: @test_umul4(
+; CHECK-NEXT:    ret { i8, i1 } zeroinitializer
+;
+  %x = call {i8, i1} @llvm.umul.with.overflow.i8(i8 undef, i8 %V)
+  ret {i8, i1} %x
+}
+
 define {i8, i1} @test_smul1(i8 %V) {
 ; CHECK-LABEL: @test_smul1(
 ; CHECK-NEXT:    ret { i8, i1 } zeroinitializer
@@ -141,6 +173,22 @@ define {i8, i1} @test_smul2(i8 %V) {
   ret {i8, i1} %x
 }
 
+define {i8, i1} @test_smul3(i8 %V) {
+; CHECK-LABEL: @test_smul3(
+; CHECK-NEXT:    ret { i8, i1 } zeroinitializer
+;
+  %x = call {i8, i1} @llvm.smul.with.overflow.i8(i8 0, i8 %V)
+  ret {i8, i1} %x
+}
+
+define {i8, i1} @test_smul4(i8 %V) {
+; CHECK-LABEL: @test_smul4(
+; CHECK-NEXT:    ret { i8, i1 } zeroinitializer
+;
+  %x = call {i8, i1} @llvm.smul.with.overflow.i8(i8 undef, i8 %V)
+  ret {i8, i1} %x
+}
+
 declare i256 @llvm.cttz.i256(i256 %src, i1 %is_zero_undef)
 
 define i256 @test_cttz() {