From 27e656c742a3aa73d4ff12a39467d3d56ff53eb3 Mon Sep 17 00:00:00 2001
From: David Majnemer <david.majnemer@gmail.com>
Date: Wed, 17 Sep 2014 03:34:34 +0000
Subject: [PATCH] InstSimplify: ((X % Y) % Y) -> (X % Y)

Patch by Sonam Kumari!

Differential Revision: http://reviews.llvm.org/D5350

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@217937 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Analysis/InstructionSimplify.cpp | 5 +++++
 test/Transforms/InstSimplify/rem.ll  | 9 +++++++++
 2 files changed, 14 insertions(+)

diff --git a/lib/Analysis/InstructionSimplify.cpp b/lib/Analysis/InstructionSimplify.cpp
index a745d14ca42..039d8286ecb 100644
--- a/lib/Analysis/InstructionSimplify.cpp
+++ b/lib/Analysis/InstructionSimplify.cpp
@@ -1171,6 +1171,11 @@ static Value *SimplifyRem(Instruction::BinaryOps Opcode, Value *Op0, Value *Op1,
   if (Op0 == Op1)
     return Constant::getNullValue(Op0->getType());
 
+  // ((X % Y) % Y) -> (X % Y)
+  if (match(Op0, m_SRem(m_Value(), m_Specific(Op1)))) {
+    return Op0;
+  }
+
   // If the operation is with the result of a select instruction, check whether
   // operating on either branch of the select always yields the same value.
   if (isa<SelectInst>(Op0) || isa<SelectInst>(Op1))
diff --git a/test/Transforms/InstSimplify/rem.ll b/test/Transforms/InstSimplify/rem.ll
index 80fa8e7b483..b757ccd6e4d 100644
--- a/test/Transforms/InstSimplify/rem.ll
+++ b/test/Transforms/InstSimplify/rem.ll
@@ -15,3 +15,12 @@ define i32 @select2(i32 %x, i1 %b) {
   ret i32 %rem
 ; CHECK: ret i32 0
 }
+
+define i32 @select3(i32 %x, i32 %n) {
+; CHECK-LABEL: @select3(
+; CHECK-NEXT: %mod = srem i32 %x, %n
+; CHECK-NEXT: ret i32 %mod
+ %mod = srem i32 %x, %n
+ %mod1 = srem i32 %mod, %n
+ ret i32 %mod1
+}