InstSimplify: div %X, 0 -> undef

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

llvm-svn: 223919

llvm/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());

llvm/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
+}