Commit 444383e0 authored by Noah Goldstein's avatar Noah Goldstein
Browse files

[ValueTracking] Do more thorough non-zero check in `isKnownToBePowerOfTwo` when `OrZero` is no set. 

We can cover more cases by directly checking if the result is
known-nonzero for common patterns when they are missing `OrZero`.

This patch add `isKnownNonZero` checks for `shl`, `lshr`, `and`, and `mul`.

Differential Revision: https://reviews.llvm.org/D157309
parent dfda65c8

llvm/lib/Analysis/ValueTracking.cpp

+12 −13
Original line number Diff line number Diff line
@@ -2061,20 +2061,19 @@ bool isKnownToBeAPowerOfTwo(const Value *V, bool OrZero, unsigned Depth, 
      return isKnownToBeAPowerOfTwo(I->getOperand(0), OrZero, Depth, Q);

    return false;

  case Instruction::Mul:

    return OrZero &&

           isKnownToBeAPowerOfTwo(I->getOperand(1), OrZero, Depth, Q) &&

           isKnownToBeAPowerOfTwo(I->getOperand(0), OrZero, Depth, Q);

    return isKnownToBeAPowerOfTwo(I->getOperand(1), OrZero, Depth, Q) &&

           isKnownToBeAPowerOfTwo(I->getOperand(0), OrZero, Depth, Q) &&

           (OrZero || isKnownNonZero(I, Depth, Q));

  case Instruction::And:

    if (OrZero) {

    // A power of two and'd with anything is a power of two or zero.

      if (isKnownToBeAPowerOfTwo(I->getOperand(1), /*OrZero*/ true, Depth, Q) ||

          isKnownToBeAPowerOfTwo(I->getOperand(0), /*OrZero*/ true, Depth, Q))

    if (OrZero &&

        (isKnownToBeAPowerOfTwo(I->getOperand(1), /*OrZero*/ true, Depth, Q) ||

         isKnownToBeAPowerOfTwo(I->getOperand(0), /*OrZero*/ true, Depth, Q)))

      return true;

    // X & (-X) is always a power of two or zero.

    if (match(I->getOperand(0), m_Neg(m_Specific(I->getOperand(1)))) ||

        match(I->getOperand(1), m_Neg(m_Specific(I->getOperand(0)))))

        return true;

    }

      return OrZero || isKnownNonZero(I->getOperand(0), Depth, Q);

    return false;

  case Instruction::Add: {

    // Adding a power-of-two or zero to the same power-of-two or zero yields

llvm/test/Analysis/ValueTracking/known-power-of-two.ll

+3 −3
Original line number Diff line number Diff line
@@ -584,9 +584,9 @@ define i1 @and_is_pow2(i16 %x, i16 %y) { 
; CHECK-SAME: (i16 [[X:%.*]], i16 [[Y:%.*]]) {

; CHECK-NEXT:    [[XNZ:%.*]] = or i16 [[X]], 4

; CHECK-NEXT:    [[X_NEG:%.*]] = sub nsw i16 0, [[XNZ]]

; CHECK-NEXT:    [[XX:%.*]] = and i16 [[XNZ]], [[X_NEG]]

; CHECK-NEXT:    [[AND:%.*]] = and i16 [[XX]], [[Y]]

; CHECK-NEXT:    [[R:%.*]] = icmp eq i16 [[AND]], [[XX]]

; CHECK-NEXT:    [[TMP1:%.*]] = and i16 [[X_NEG]], [[Y]]

; CHECK-NEXT:    [[AND:%.*]] = and i16 [[TMP1]], [[XNZ]]

; CHECK-NEXT:    [[R:%.*]] = icmp ne i16 [[AND]], 0

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

;

  %xnz = or i16 %x, 4

llvm/test/Transforms/InstSimplify/ctpop-pow2.ll

+1 −4
Original line number Diff line number Diff line
@@ -41,10 +41,7 @@ define i16 @ctpop_x_and_negx(i16 %x) { 


define i8 @ctpop_x_nz_and_negx(i8 %x) {

; CHECK-LABEL: @ctpop_x_nz_and_negx(

; CHECK-NEXT:    [[X1:%.*]] = or i8 [[X:%.*]], 1

; CHECK-NEXT:    [[V0:%.*]] = sub i8 0, [[X1]]

; CHECK-NEXT:    [[V1:%.*]] = and i8 [[X1]], [[V0]]

; CHECK-NEXT:    ret i8 [[V1]]

; CHECK-NEXT:    ret i8 1

;

  %x1 = or i8 %x, 1

  %v0 = sub i8 0, %x1