[PATCH] D49423: [InstSimplify] fold srem instruction if its two operands are negatived.

[ChenZheng via Phabricator via llvm-commits]

shchenz created this revision.
shchenz added reviewers: lebedev.ri, nemanjai, majnemer.
Herald added a subscriber: hiraditya.

This is from code review comment from https://reviews.llvm.org/D49382. We already finish related optimization for add instruction in https://reviews.llvm.org/D49216 and sdiv instruction in https://reviews.llvm.org/D49382.

This patch is for srem instruction. for example:

  define i32 @negated_operand(i32 %x) {
    %negx = sub i32 0, %x
    %rem = srem i32 %negx, %x
    ret i32 %rem 
  }

can be folded to:

  define i32 @negated_operand(i32 %x) {
    ret i32 0
  }

Alive verification:
https://rise4fun.com/Alive/q20
https://rise4fun.com/Alive/h4o


https://reviews.llvm.org/D49423

Files:
  llvm/lib/Analysis/InstructionSimplify.cpp
  llvm/test/Transforms/InstSimplify/srem.ll


Index: llvm/test/Transforms/InstSimplify/srem.ll
===================================================================
--- llvm/test/Transforms/InstSimplify/srem.ll
+++ llvm/test/Transforms/InstSimplify/srem.ll
@@ -2,32 +2,25 @@
 
 define i32 @negated_operand(i32 %x) {
 ; CHECK-LABEL: @negated_operand(
-; CHECK-NEXT:    [[NEGX:%.*]] = sub i32 0, [[X:%.*]]
-; CHECK-NEXT:    [[REM:%.*]] = srem i32 [[NEGX]], [[X]]
-; CHECK-NEXT:    ret i32 [[REM]]
+; CHECK-NEXT:    ret i32 0
 ;
   %negx = sub i32 0, %x
   %rem = srem i32 %negx, %x
   ret i32 %rem
 }
 
 define <2 x i32> @negated_operand_commute_vec(<2 x i32> %x) {
 ; CHECK-LABEL: @negated_operand_commute_vec(
-; CHECK-NEXT:    [[NEGX:%.*]] = sub nsw <2 x i32> zeroinitializer, [[X:%.*]]
-; CHECK-NEXT:    [[REM:%.*]] = srem <2 x i32> [[NEGX]], [[X]]
-; CHECK-NEXT:    ret <2 x i32> [[REM]]
+; CHECK-NEXT:    ret <2 x i32> zeroinitializer
 ;
   %negx = sub nsw <2 x i32> zeroinitializer, %x
   %rem = srem <2 x i32> %negx, %x
   ret <2 x i32> %rem
 }
 
 define i32 @knownnegation(i32 %x, i32 %y) {
 ; CHECK-LABEL: @knownnegation(
-; CHECK-NEXT:    [[XY:%.*]] = sub nsw i32 [[X:%.*]], [[Y:%.*]]
-; CHECK-NEXT:    [[YX:%.*]] = sub nsw i32 [[Y]], [[X]]
-; CHECK-NEXT:    [[REM:%.*]] = srem i32 [[XY]], [[YX]]
-; CHECK-NEXT:    ret i32 [[REM]]
+; CHECK-NEXT:    ret i32 0
 ;
   %xy = sub nsw i32 %x, %y
   %yx = sub nsw i32 %y, %x
@@ -37,10 +30,7 @@
 
 define <2 x i32> @knownnegation_commute_vec(<2 x i32> %x, <2 x i32> %y) {
 ; CHECK-LABEL: @knownnegation_commute_vec(
-; CHECK-NEXT:    [[XY:%.*]] = sub nsw <2 x i32> [[X:%.*]], [[Y:%.*]]
-; CHECK-NEXT:    [[YX:%.*]] = sub nsw <2 x i32> [[Y]], [[X]]
-; CHECK-NEXT:    [[REM:%.*]] = srem <2 x i32> [[XY]], [[YX]]
-; CHECK-NEXT:    ret <2 x i32> [[REM]]
+; CHECK-NEXT:    ret <2 x i32> zeroinitializer
 ;
   %xy = sub nsw <2 x i32> %x, %y
   %yx = sub nsw <2 x i32> %y, %x
Index: llvm/lib/Analysis/InstructionSimplify.cpp
===================================================================
--- llvm/lib/Analysis/InstructionSimplify.cpp
+++ llvm/lib/Analysis/InstructionSimplify.cpp
@@ -1109,6 +1109,10 @@
   if (match(Op1, m_SExt(m_Value(X))) && X->getType()->isIntOrIntVectorTy(1))
     return ConstantInt::getNullValue(Op0->getType());
 
+  // If the two operands are negatived, return 0.
+  if (isKnownNegation(Op0, Op1))
+    return ConstantInt::getNullValue(Op0->getType());
+
   return simplifyRem(Instruction::SRem, Op0, Op1, Q, MaxRecurse);
 }
 


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