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[KnownBits] Add KnownBits::makeConstant helper. NFCI.

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Helper for cases where we need to create a KnownBits from a (fully known) constant value.
This commit is contained in:
Simon Pilgrim 2020-11-12 16:15:46 +00:00
parent 27b1315bd4
commit b22745774c
3 changed files with 10 additions and 18 deletions
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5
include/llvm/Support/KnownBits.h
View File

@ -250,6 +250,11 @@ public:
return getBitWidth() - Zero.countPopulation();
}
/// Create known bits from a known constant.
static KnownBits makeConstant(const APInt &C) {
return KnownBits(~C, C);
}
/// Compute known bits common to LHS and RHS.
static KnownBits commonBits(const KnownBits &LHS, const KnownBits &RHS) {
return KnownBits(LHS.Zero & RHS.Zero, LHS.One & RHS.One);

15
lib/Analysis/ValueTracking.cpp
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@ -1223,10 +1223,7 @@ static void computeKnownBitsFromOperator(const Operator *I,
case Instruction::Shl: {
bool NSW = Q.IIQ.hasNoSignedWrap(cast<OverflowingBinaryOperator>(I));
auto KF = [NSW](const KnownBits &KnownShiftVal, unsigned ShiftAmt) {
APInt ShiftAmtV(KnownShiftVal.getBitWidth(), ShiftAmt);
KnownBits KnownShiftAmt;
KnownShiftAmt.One = ShiftAmtV;
KnownShiftAmt.Zero = ~ShiftAmtV;
KnownBits KnownShiftAmt = KnownBits::makeConstant(APInt(32, ShiftAmt));
KnownBits Result = KnownBits::shl(KnownShiftVal, KnownShiftAmt);
// If this shift has "nsw" keyword, then the result is either a poison
// value or has the same sign bit as the first operand.
@ -1244,10 +1241,7 @@ static void computeKnownBitsFromOperator(const Operator *I,
}
case Instruction::LShr: {
auto KF = [](const KnownBits &KnownShiftVal, unsigned ShiftAmt) {
APInt ShiftAmtV(KnownShiftVal.getBitWidth(), ShiftAmt);
KnownBits KnownShiftAmt;
KnownShiftAmt.One = ShiftAmtV;
KnownShiftAmt.Zero = ~ShiftAmtV;
KnownBits KnownShiftAmt = KnownBits::makeConstant(APInt(32, ShiftAmt));
return KnownBits::lshr(KnownShiftVal, KnownShiftAmt);
};
computeKnownBitsFromShiftOperator(I, DemandedElts, Known, Known2, Depth, Q,
@ -1256,10 +1250,7 @@ static void computeKnownBitsFromOperator(const Operator *I,
}
case Instruction::AShr: {
auto KF = [](const KnownBits &KnownShiftVal, unsigned ShiftAmt) {
APInt ShiftAmtV(KnownShiftVal.getBitWidth(), ShiftAmt);
KnownBits KnownShiftAmt;
KnownShiftAmt.One = ShiftAmtV;
KnownShiftAmt.Zero = ~ShiftAmtV;
KnownBits KnownShiftAmt = KnownBits::makeConstant(APInt(32, ShiftAmt));
return KnownBits::ashr(KnownShiftVal, KnownShiftAmt);
};
computeKnownBitsFromShiftOperator(I, DemandedElts, Known, Known2, Depth, Q,

8
lib/CodeGen/SelectionDAG/SelectionDAG.cpp
View File

@ -2624,15 +2624,11 @@ KnownBits SelectionDAG::computeKnownBits(SDValue Op, const APInt &DemandedElts,
if (auto *C = dyn_cast<ConstantSDNode>(Op)) {
// We know all of the bits for a constant!
Known.One = C->getAPIntValue();
Known.Zero = ~Known.One;
return Known;
return KnownBits::makeConstant(C->getAPIntValue());
}
if (auto *C = dyn_cast<ConstantFPSDNode>(Op)) {
// We know all of the bits for a constant fp!
Known.One = C->getValueAPF().bitcastToAPInt();
Known.Zero = ~Known.One;
return Known;
return KnownBits::makeConstant(C->getValueAPF().bitcastToAPInt());
}
if (Depth >= MaxRecursionDepth)