[llvm] r217939 - InstSimplify: Don't allow (x srem y) urem y -> x srem y

[David Majnemer]

Author: majnemer
Date: Tue Sep 16 23:16:35 2014
New Revision: 217939

URL: http://llvm.org/viewvc/llvm-project?rev=217939&view=rev
Log:
InstSimplify: Don't allow (x srem y) urem y -> x srem y

Let's consider the case where:
%x i16 = 32768
%y i16 = 384

%x srem %y = 65408
(%x srem %y) urem %y = 128

Modified:
    llvm/trunk/lib/Analysis/InstructionSimplify.cpp
    llvm/trunk/test/Transforms/InstSimplify/rem.ll

Modified: llvm/trunk/lib/Analysis/InstructionSimplify.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/InstructionSimplify.cpp?rev=217939&r1=217938&r2=217939&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/InstructionSimplify.cpp (original)
+++ llvm/trunk/lib/Analysis/InstructionSimplify.cpp Tue Sep 16 23:16:35 2014
@@ -1171,10 +1171,12 @@ static Value *SimplifyRem(Instruction::B
   if (Op0 == Op1)
     return Constant::getNullValue(Op0->getType());
 
-  // ((X % Y) % Y) -> (X % Y)
-  if (match(Op0, m_SRem(m_Value(), m_Specific(Op1)))) {
+  // (X % Y) % Y -> X % Y
+  if ((Opcode == Instruction::SRem &&
+       match(Op0, m_SRem(m_Value(), m_Specific(Op1)))) ||
+      (Opcode == Instruction::URem &&
+       match(Op0, m_URem(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.

Modified: llvm/trunk/test/Transforms/InstSimplify/rem.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstSimplify/rem.ll?rev=217939&r1=217938&r2=217939&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstSimplify/rem.ll (original)
+++ llvm/trunk/test/Transforms/InstSimplify/rem.ll Tue Sep 16 23:16:35 2014
@@ -16,11 +16,30 @@ define i32 @select2(i32 %x, i1 %b) {
 ; CHECK: ret i32 0
 }
 
-define i32 @select3(i32 %x, i32 %n) {
-; CHECK-LABEL: @select3(
+define i32 @rem1(i32 %x, i32 %n) {
+; CHECK-LABEL: @rem1(
 ; 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
 }
+
+define i32 @rem2(i32 %x, i32 %n) {
+; CHECK-LABEL: @rem2(
+; CHECK-NEXT: %mod = urem i32 %x, %n
+; CHECK-NEXT: ret i32 %mod
+ %mod = urem i32 %x, %n
+ %mod1 = urem i32 %mod, %n
+ ret i32 %mod1
+}
+
+define i32 @rem3(i32 %x, i32 %n) {
+; CHECK-LABEL: @rem3(
+; CHECK-NEXT: %[[srem:.*]] = srem i32 %x, %n
+; CHECK-NEXT: %[[urem:.*]] = urem i32 %[[srem]], %n
+; CHECK-NEXT: ret i32 %[[urem]]
+ %mod = srem i32 %x, %n
+ %mod1 = urem i32 %mod, %n
+ ret i32 %mod1
+}