Unverified Commit dfe1d35c authored by Yingwei Zheng's avatar Yingwei Zheng Committed by GitHub
Browse files

[InstCombine] Propagate NSW/NUW flags for `(X - Y) - Z -> X - (Y + Z)` (#72693) 

Alive2: https://alive2.llvm.org/ce/z/gqeaVo

Related patch:
https://github.com/llvm/llvm-project/commit/31d219d2997fed1b7dc97e0adf170d5aaf65883e
parent 5a305cea

llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp

+9 −2
Original line number Diff line number Diff line
@@ -2191,8 +2191,15 @@ Instruction *InstCombinerImpl::visitSub(BinaryOperator &I) { 


  // ((X - Y) - Op1)  -->  X - (Y + Op1)

  if (match(Op0, m_OneUse(m_Sub(m_Value(X), m_Value(Y))))) {

    Value *Add = Builder.CreateAdd(Y, Op1);

    return BinaryOperator::CreateSub(X, Add);

    OverflowingBinaryOperator *LHSSub = cast<OverflowingBinaryOperator>(Op0);

    bool HasNUW = I.hasNoUnsignedWrap() && LHSSub->hasNoUnsignedWrap();

    bool HasNSW = HasNUW && I.hasNoSignedWrap() && LHSSub->hasNoSignedWrap();

    Value *Add = Builder.CreateAdd(Y, Op1, "", /* HasNUW */ HasNUW,

                                   /* HasNSW */ HasNSW);

    BinaryOperator *Sub = BinaryOperator::CreateSub(X, Add);

    Sub->setHasNoUnsignedWrap(HasNUW);

    Sub->setHasNoSignedWrap(HasNSW);

    return Sub;

  }



  // (~X) - (~Y) --> Y - X

llvm/test/Transforms/InstCombine/sub-from-sub.ll

+69 −1
Original line number Diff line number Diff line
@@ -17,14 +17,82 @@ define i8 @t0(i8 %x, i8 %y, i8 %z) { 
  ret i8 %r

}



; No flags are propagated

; NSW/NUW flags are propagated

define i8 @t1_flags(i8 %x, i8 %y, i8 %z) {

; CHECK-LABEL: @t1_flags(

; CHECK-NEXT:    [[TMP1:%.*]] = add nuw nsw i8 [[Y:%.*]], [[Z:%.*]]

; CHECK-NEXT:    [[R:%.*]] = sub nuw nsw i8 [[X:%.*]], [[TMP1]]

; CHECK-NEXT:    ret i8 [[R]]

;

  %o0 = sub nuw nsw i8 %x, %y

  %r = sub nuw nsw i8 %o0, %z

  ret i8 %r

}



; NUW flags are propagated

define i8 @t1_flags_nuw_only(i8 %x, i8 %y, i8 %z) {

; CHECK-LABEL: @t1_flags_nuw_only(

; CHECK-NEXT:    [[TMP1:%.*]] = add nuw i8 [[Y:%.*]], [[Z:%.*]]

; CHECK-NEXT:    [[R:%.*]] = sub nuw i8 [[X:%.*]], [[TMP1]]

; CHECK-NEXT:    ret i8 [[R]]

;

  %o0 = sub nuw i8 %x, %y

  %r = sub nuw i8 %o0, %z

  ret i8 %r

}



; Negative tests

define i8 @t1_flags_sub_nsw_sub(i8 %x, i8 %y, i8 %z) {

; CHECK-LABEL: @t1_flags_sub_nsw_sub(

; CHECK-NEXT:    [[TMP1:%.*]] = add i8 [[Y:%.*]], [[Z:%.*]]

; CHECK-NEXT:    [[R:%.*]] = sub i8 [[X:%.*]], [[TMP1]]

; CHECK-NEXT:    ret i8 [[R]]

;

  %o0 = sub nsw i8 %x, %y

  %r = sub i8 %o0, %z

  ret i8 %r

}



define i8 @t1_flags_nuw_first(i8 %x, i8 %y, i8 %z) {

; CHECK-LABEL: @t1_flags_nuw_first(

; CHECK-NEXT:    [[TMP1:%.*]] = add i8 [[Y:%.*]], [[Z:%.*]]

; CHECK-NEXT:    [[R:%.*]] = sub i8 [[X:%.*]], [[TMP1]]

; CHECK-NEXT:    ret i8 [[R]]

;

  %o0 = sub nuw i8 %x, %y

  %r = sub i8 %o0, %z

  ret i8 %r

}



define i8 @t1_flags_nuw_second(i8 %x, i8 %y, i8 %z) {

; CHECK-LABEL: @t1_flags_nuw_second(

; CHECK-NEXT:    [[TMP1:%.*]] = add i8 [[Y:%.*]], [[Z:%.*]]

; CHECK-NEXT:    [[R:%.*]] = sub i8 [[X:%.*]], [[TMP1]]

; CHECK-NEXT:    ret i8 [[R]]

;

  %o0 = sub i8 %x, %y

  %r = sub nuw i8 %o0, %z

  ret i8 %r

}



define i8 @t1_flags_nuw_nsw_first(i8 %x, i8 %y, i8 %z) {

; CHECK-LABEL: @t1_flags_nuw_nsw_first(

; CHECK-NEXT:    [[TMP1:%.*]] = add i8 [[Y:%.*]], [[Z:%.*]]

; CHECK-NEXT:    [[R:%.*]] = sub i8 [[X:%.*]], [[TMP1]]

; CHECK-NEXT:    ret i8 [[R]]

;

  %o0 = sub nuw nsw i8 %x, %y

  %r = sub i8 %o0, %z

  ret i8 %r

}



define i8 @t1_flags_nuw_nsw_second(i8 %x, i8 %y, i8 %z) {

; CHECK-LABEL: @t1_flags_nuw_nsw_second(

; CHECK-NEXT:    [[TMP1:%.*]] = add i8 [[Y:%.*]], [[Z:%.*]]

; CHECK-NEXT:    [[R:%.*]] = sub i8 [[X:%.*]], [[TMP1]]

; CHECK-NEXT:    ret i8 [[R]]

;

  %o0 = sub i8 %x, %y

  %r = sub nuw nsw i8 %o0, %z

  ret i8 %r

}