InstSimplify: ((X % Y) % Y) -> (X % Y)

Patch by Sonam Kumari!

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

llvm-svn: 217937

2 files changed, 14 insertions, 0 deletions

diff --git a/llvm/lib/Analysis/InstructionSimplify.cpp b/llvm/lib/Analysis/InstructionSimplify.cpp
index a745d14ca42..039d8286ecb 100644
--- a/llvm/lib/Analysis/InstructionSimplify.cpp
+++ b/llvm/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/llvm/test/Transforms/InstSimplify/rem.ll b/llvm/test/Transforms/InstSimplify/rem.ll
index 80fa8e7b483..b757ccd6e4d 100644
--- a/llvm/test/Transforms/InstSimplify/rem.ll
+++ b/llvm/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
+}