[InstCombine] Canonicalize (-X srem Y) to -(X srem Y)

[shchenz]

Summary

Similar with https://reviews.llvm.org/D60395.

This is for operator srem.

Fix https://bugs.llvm.org/show_bug.cgi?id=41443

[lebedev.ri]

LGTM, thank you

llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp

1354

----------------------------------------
Optimization: tests
Precondition: true
  %o0 = sub nsw i8 0, %x
  %r = srem i8 %o0, %y
=>
  %n0 = srem i8 %x, %y
  %r = sub nsw i8 0, %n0

Done: 1
Optimization is correct!

llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp

Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
     // X % -Y -> X % Y
     if (match(Op1, m_Negative(Y)) && !Y->isMinSignedValue()) {
       Worklist.AddValue(I.getOperand(1));
       I.setOperand(1, ConstantInt::get(I.getType(), -*Y));
       return &I;
     }
   }
 
+  // -X srem Y --> -(X srem Y)
+  Value *X, *Y;
+  if (match(&I, m_SRem(m_OneUse(m_NSWSub(m_Zero(), m_Value(X))), m_Value(Y))))
+    return BinaryOperator::CreateNSWNeg(Builder.CreateSRem(X, Y)); 
+
   // If the sign bits of both operands are zero (i.e. we can prove they are
   // unsigned inputs), turn this into a urem.
   APInt Mask(APInt::getSignMask(I.getType()->getScalarSizeInBits()));
   if (MaskedValueIsZero(Op1, Mask, 0, &I) &&
       MaskedValueIsZero(Op0, Mask, 0, &I)) {
     // X srem Y -> X urem Y, iff X and Y don't have sign bit set
     return BinaryOperator::CreateURem(Op0, Op1, I.getName());
   }

llvm/test/Transforms/InstCombine/srem-canonicalize.ll

 ; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
 ; RUN: opt < %s -instcombine -S | FileCheck %s
 
 define i32 @test_srem_canonicalize_op0(i32 %x, i32 %y) {
 ; CHECK-LABEL: @test_srem_canonicalize_op0(
-; CHECK-NEXT:    [[NEG:%.*]] = sub nsw i32 0, [[X:%.*]]
-; CHECK-NEXT:    [[SREM:%.*]] = srem i32 [[NEG]], [[Y:%.*]]
+; CHECK-NEXT:    [[TMP1:%.*]] = srem i32 [[X:%.*]], [[Y:%.*]]
+; CHECK-NEXT:    [[SREM:%.*]] = sub nsw i32 0, [[TMP1]]
 ; CHECK-NEXT:    ret i32 [[SREM]]
 ;
   %neg = sub nsw i32 0, %x
   %srem = srem i32 %neg, %y
   ret i32 %srem
 }
 
 ; (X srem -Y) is not equal to -(X srem Y), don't canonicalize.

 ;
   %neg = sub i32 0, %x
   %srem = srem i32 %neg, %y
   ret i32 %srem
 }
 
 define <2 x i32> @test_srem_canonicalize_vec(<2 x i32> %x, <2 x i32> %y) {
 ; CHECK-LABEL: @test_srem_canonicalize_vec(
-; CHECK-NEXT:    [[NEG:%.*]] = sub nsw <2 x i32> zeroinitializer, [[X:%.*]]
-; CHECK-NEXT:    [[SREM:%.*]] = srem <2 x i32> [[NEG]], [[Y:%.*]]
+; CHECK-NEXT:    [[TMP1:%.*]] = srem <2 x i32> [[X:%.*]], [[Y:%.*]]
+; CHECK-NEXT:    [[SREM:%.*]] = sub nsw <2 x i32> zeroinitializer, [[TMP1]]
 ; CHECK-NEXT:    ret <2 x i32> [[SREM]]
 ;
   %neg = sub nsw <2 x i32> <i32 0, i32 0>, %x
   %srem = srem <2 x i32> %neg, %y
   ret <2 x i32> %srem
 }
 
 define i32 @test_srem_canonicalize_multiple_uses(i32 %x, i32 %y) {