Added InstCombine transform for pattern " ((X % Y) % Y) -> (X % Y) ".

[sonamkumari]

Summary

Hi All,

This patch implements transform for the pattern " ((X % Y) % Y) -> (X % Y) "

Please help in reviewing the same.

Thanks,
Sonam.

[majnemer]

This doesn't introduce any new instructions, move it to InstSimplify.

[sonamkumari]

Hi David,

Thanks for your review comments.
I have made the changes as per your comments and resubmitted the patch.
Kindly review it. :)

Regards,
Sonam.

[majnemer]

lib/Analysis/InstructionSimplify.cpp

1174 ↗

(On Diff #13736)

This can just be:
if (match(Op0, m_SRem(m_Value(), m_Specific(Op1)))) {

[sonamkumari]

Hi David,

Resubmitted the patch based on your comments.
Kindly review it. :)

Regards,
Sonam.

[majnemer]

LGTM.

[sonamkumari]

Hi David,

Thanks for your consistent time and support. :)
Can you please commit this patch.

Regards,
Sonam.

[majnemer]

Closed by commit rL217937 (authored by @majnemer).

llvm/trunk/lib/Analysis/InstructionSimplify.cpp

static Value *SimplifyRem(Instruction::BinaryOps Opcode, Value *Op0, Value *Op1,
   if (Op0->getType()->isIntegerTy(1))
     // It can't be remainder by zero, hence it must be remainder by one.
     return Constant::getNullValue(Op0->getType());
 
   // X % X -> 0
   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))
     if (Value *V = ThreadBinOpOverSelect(Opcode, Op0, Op1, Q, MaxRecurse))
       return V;
 
   // If the operation is with the result of a phi instruction, check whether
   // operating on all incoming values of the phi always yields the same value.

llvm/trunk/test/Transforms/InstSimplify/rem.ll

 
 define i32 @select2(i32 %x, i1 %b) {
 ; CHECK-LABEL: @select2(
   %rhs = select i1 %b, i32 %x, i32 1
   %rem = urem i32 %x, %rhs
   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
+}