From 75681bb302e524460edb7c8c5c6e98792b5027a2 Mon Sep 17 00:00:00 2001
From: Nick Lewycky <nicholas@mxc.ca>
Date: Sat, 13 Jul 2013 01:16:47 +0000
Subject: [PATCH] Add a microoptimization for urem.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@186235 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Transforms/InstCombine/InstCombineMulDivRem.cpp | 7 +++++++
 test/Transforms/InstCombine/rem.ll                  | 9 +++++++++
 2 files changed, 16 insertions(+)

diff --git a/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp b/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
index e94f71917f5..eac24c63451 100644
--- a/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
+++ b/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
@@ -1125,6 +1125,13 @@ Instruction *InstCombiner::visitURem(BinaryOperator &I) {
     return BinaryOperator::CreateAnd(Op0, Add);
   }
 
+  // 1 urem X -> zext(X != 1)
+  if (match(Op0, m_One())) {
+    Value *Cmp = Builder->CreateICmpNE(Op1, Op0);
+    Value *Ext = Builder->CreateZExt(Cmp, I.getType());
+    return ReplaceInstUsesWith(I, Ext);
+  }
+
   return 0;
 }
 
diff --git a/test/Transforms/InstCombine/rem.ll b/test/Transforms/InstCombine/rem.ll
index 808d51eba1d..c6fd7211995 100644
--- a/test/Transforms/InstCombine/rem.ll
+++ b/test/Transforms/InstCombine/rem.ll
@@ -163,3 +163,12 @@ define i32 @test16(i32 %x, i32 %y) {
 	%rem = urem i32 %x, %add
 	ret i32 %rem
 }
+
+define i32 @test17(i32 %X) {
+; CHECK: @test17
+; CHECK-NEXT: icmp ne i32 %X, 1
+; CHECK-NEXT: zext i1
+; CHECK-NEXT: ret
+  %A = urem i32 1, %X
+  ret i32 %A
+}