Commit 5eedfff6 authored by Noah Goldstein's avatar Noah Goldstein
Browse files

[ValueTracking] Add additional cases for `isKnownNonZero(mul X, Y)` 

If either `X` or `Y` is odd and the other is non-zero, the result is
non-zero.

Alive2 Link:
    https://alive2.llvm.org/ce/z/9V7-es

Reviewed By: nikic

Differential Revision: https://reviews.llvm.org/D149418
parent d8403914

llvm/lib/Analysis/ValueTracking.cpp

+18 −5
Original line number Diff line number Diff line
@@ -2872,11 +2872,24 @@ bool isKnownNonZero(const Value *V, const APInt &DemandedElts, unsigned Depth, 
    // If X and Y are non-zero then so is X * Y as long as the multiplication

    // does not overflow.

    const OverflowingBinaryOperator *BO = cast<OverflowingBinaryOperator>(V);

    if ((Q.IIQ.hasNoSignedWrap(BO) || Q.IIQ.hasNoUnsignedWrap(BO)) &&

        isKnownNonZero(I->getOperand(0), DemandedElts, Depth, Q) &&

        isKnownNonZero(I->getOperand(1), DemandedElts, Depth, Q))

      return true;

    break;

    if (Q.IIQ.hasNoSignedWrap(BO) || Q.IIQ.hasNoUnsignedWrap(BO))

      return isKnownNonZero(I->getOperand(0), DemandedElts, Depth, Q) &&

             isKnownNonZero(I->getOperand(1), DemandedElts, Depth, Q);



    // If either X or Y is odd, then if the other is non-zero the result can't

    // be zero.

    KnownBits XKnown =

        computeKnownBits(I->getOperand(0), DemandedElts, Depth, Q);

    if (XKnown.One[0])

      return isKnownNonZero(I->getOperand(1), DemandedElts, Depth, Q);



    KnownBits YKnown =

        computeKnownBits(I->getOperand(1), DemandedElts, Depth, Q);

    if (YKnown.One[0])

      return XKnown.isNonZero() ||

             isKnownNonZero(I->getOperand(0), DemandedElts, Depth, Q);



    return KnownBits::mul(XKnown, YKnown).isNonZero();

  }

  case Instruction::Select:

    // (C ? X : Y) != 0 if X != 0 and Y != 0.

llvm/test/Analysis/ValueTracking/known-non-zero.ll

+1 −5
Original line number Diff line number Diff line
@@ -767,13 +767,9 @@ define i1 @cttz_nonzero_fail_maybe_odd(i8 %xx, i8 %cnt, i8 %ind) { 


define i1 @mul_nonzero_odd(i8 %xx, i8 %y, i8 %ind) {

; CHECK-LABEL: @mul_nonzero_odd(

; CHECK-NEXT:    [[XO:%.*]] = or i8 [[XX:%.*]], 1

; CHECK-NEXT:    [[Y_NZ:%.*]] = icmp ne i8 [[Y:%.*]], 0

; CHECK-NEXT:    call void @llvm.assume(i1 [[Y_NZ]])

; CHECK-NEXT:    [[X:%.*]] = mul i8 [[XO]], [[Y]]

; CHECK-NEXT:    [[Z:%.*]] = or i8 [[X]], [[IND:%.*]]

; CHECK-NEXT:    [[R:%.*]] = icmp eq i8 [[Z]], 0

; CHECK-NEXT:    ret i1 [[R]]

; CHECK-NEXT:    ret i1 false

;

  %xo = or i8 %xx, 1

  %y_nz = icmp ne i8 %y, 0