From 8ec2668c750a266f194302fc46b15aacdf56f407 Mon Sep 17 00:00:00 2001
From: David Majnemer <david.majnemer@gmail.com>
Date: Wed, 10 Dec 2014 07:52:18 +0000
Subject: [PATCH] InstSimplify: div %X, 0 -> undef

We already optimized rem %X, 0 to undef, we should do the same for div.

llvm-svn: 223919
---
 lib/Analysis/InstructionSimplify.cpp  |  4 ++++
 test/Transforms/InstSimplify/undef.ll | 14 ++++++++++++++
 2 files changed, 18 insertions(+)

diff --git a/lib/Analysis/InstructionSimplify.cpp b/lib/Analysis/InstructionSimplify.cpp
index 2cf1661cfd9..767b42b4bd7 100644
--- a/lib/Analysis/InstructionSimplify.cpp
+++ b/lib/Analysis/InstructionSimplify.cpp
@@ -1011,6 +1011,10 @@ static Value *SimplifyDiv(Instruction::BinaryOps Opcode, Value *Op0, Value *Op1,
   if (match(Op1, m_Undef()))
     return Op1;
 
+  // X / 0 -> undef, we don't need to preserve faults!
+  if (match(Op1, m_Zero()))
+    return UndefValue::get(Op1->getType());
+
   // undef / X -> 0
   if (match(Op0, m_Undef()))
     return Constant::getNullValue(Op0->getType());
diff --git a/test/Transforms/InstSimplify/undef.ll b/test/Transforms/InstSimplify/undef.ll
index 181c2efa2dc..a6ae7a9fbf7 100644
--- a/test/Transforms/InstSimplify/undef.ll
+++ b/test/Transforms/InstSimplify/undef.ll
@@ -160,3 +160,17 @@ define <4 x i8> @test19(<4 x i8> %a) {
   %b = shl <4 x i8> %a, <i8 8, i8 9, i8 undef, i8 -1>
   ret <4 x i8> %b
 }
+
+; CHECK-LABEL: @test20
+; CHECK: ret i32 undef
+define i32 @test20(i32 %a) {
+  %b = udiv i32 %a, 0
+  ret i32 %b
+}
+
+; CHECK-LABEL: @test21
+; CHECK: ret i32 undef
+define i32 @test21(i32 %a) {
+  %b = sdiv i32 %a, 0
+  ret i32 %b
+}