diff options
Diffstat (limited to 'llvm/lib/Support/KnownBits.cpp')
| -rw-r--r-- | llvm/lib/Support/KnownBits.cpp | 28 |
1 files changed, 26 insertions, 2 deletions
diff --git a/llvm/lib/Support/KnownBits.cpp b/llvm/lib/Support/KnownBits.cpp index ed25e52..c33c368 100644 --- a/llvm/lib/Support/KnownBits.cpp +++ b/llvm/lib/Support/KnownBits.cpp @@ -343,7 +343,7 @@ KnownBits KnownBits::shl(const KnownBits &LHS, const KnownBits &RHS, bool NUW, } KnownBits KnownBits::lshr(const KnownBits &LHS, const KnownBits &RHS, - bool ShAmtNonZero, bool /*Exact*/) { + bool ShAmtNonZero, bool Exact) { unsigned BitWidth = LHS.getBitWidth(); auto ShiftByConst = [&](const KnownBits &LHS, unsigned ShiftAmt) { KnownBits Known = LHS; @@ -367,6 +367,18 @@ KnownBits KnownBits::lshr(const KnownBits &LHS, const KnownBits &RHS, // Find the common bits from all possible shifts. APInt MaxValue = RHS.getMaxValue(); unsigned MaxShiftAmount = getMaxShiftAmount(MaxValue, BitWidth); + + // If exact, bound MaxShiftAmount to first known 1 in LHS. + if (Exact) { + unsigned FirstOne = LHS.countMaxTrailingZeros(); + if (FirstOne < MinShiftAmount) { + // Always poison. Return zero because we don't like returning conflict. + Known.setAllZero(); + return Known; + } + MaxShiftAmount = std::min(MaxShiftAmount, FirstOne); + } + unsigned ShiftAmtZeroMask = RHS.Zero.zextOrTrunc(32).getZExtValue(); unsigned ShiftAmtOneMask = RHS.One.zextOrTrunc(32).getZExtValue(); Known.Zero.setAllBits(); @@ -389,7 +401,7 @@ KnownBits KnownBits::lshr(const KnownBits &LHS, const KnownBits &RHS, } KnownBits KnownBits::ashr(const KnownBits &LHS, const KnownBits &RHS, - bool ShAmtNonZero, bool /*Exact*/) { + bool ShAmtNonZero, bool Exact) { unsigned BitWidth = LHS.getBitWidth(); auto ShiftByConst = [&](const KnownBits &LHS, unsigned ShiftAmt) { KnownBits Known = LHS; @@ -415,6 +427,18 @@ KnownBits KnownBits::ashr(const KnownBits &LHS, const KnownBits &RHS, // Find the common bits from all possible shifts. APInt MaxValue = RHS.getMaxValue(); unsigned MaxShiftAmount = getMaxShiftAmount(MaxValue, BitWidth); + + // If exact, bound MaxShiftAmount to first known 1 in LHS. + if (Exact) { + unsigned FirstOne = LHS.countMaxTrailingZeros(); + if (FirstOne < MinShiftAmount) { + // Always poison. Return zero because we don't like returning conflict. + Known.setAllZero(); + return Known; + } + MaxShiftAmount = std::min(MaxShiftAmount, FirstOne); + } + unsigned ShiftAmtZeroMask = RHS.Zero.zextOrTrunc(32).getZExtValue(); unsigned ShiftAmtOneMask = RHS.One.zextOrTrunc(32).getZExtValue(); Known.Zero.setAllBits(); |