[llvm] r339515 - [InstSimplify] Guard against large shift amounts.

[Hans Wennborg via llvm-commits]

Merged to 7.0 in r339985.

On Sun, Aug 12, 2018 at 1:43 PM, Benjamin Kramer via llvm-commits
<llvm-commits at lists.llvm.org> wrote:
> Author: d0k
> Date: Sun Aug 12 04:43:03 2018
> New Revision: 339515
>
> URL: http://llvm.org/viewvc/llvm-project?rev=339515&view=rev
> Log:
> [InstSimplify] Guard against large shift amounts.
>
> These are always UB, but can happen for large integer inputs. Testing it
> is very fragile as -simplifycfg will nuke the UB top-down.
>
> Modified:
>     llvm/trunk/lib/Analysis/InstructionSimplify.cpp
>
> Modified: llvm/trunk/lib/Analysis/InstructionSimplify.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/InstructionSimplify.cpp?rev=339515&r1=339514&r2=339515&view=diff
> ==============================================================================
> --- llvm/trunk/lib/Analysis/InstructionSimplify.cpp (original)
> +++ llvm/trunk/lib/Analysis/InstructionSimplify.cpp Sun Aug 12 04:43:03 2018
> @@ -1338,7 +1338,7 @@ static Value *SimplifyLShrInst(Value *Op
>      const KnownBits YKnown = computeKnownBits(Y, Q.DL, 0, Q.AC, Q.CxtI, Q.DT);
>      const unsigned Width = Op0->getType()->getScalarSizeInBits();
>      const unsigned EffWidthY = Width - YKnown.countMinLeadingZeros();
> -    if (EffWidthY <= ShRAmt->getZExtValue())
> +    if (ShRAmt->uge(EffWidthY))
>        return X;
>    }
>
> @@ -1880,9 +1880,9 @@ static Value *SimplifyAndInst(Value *Op0
>        match(Op0, m_c_Or(m_CombineAnd(m_NUWShl(m_Value(X), m_APInt(ShAmt)),
>                                       m_Value(XShifted)),
>                          m_Value(Y)))) {
> -    const unsigned ShftCnt = ShAmt->getZExtValue();
> -    const KnownBits YKnown = computeKnownBits(Y, Q.DL, 0, Q.AC, Q.CxtI, Q.DT);
>      const unsigned Width = Op0->getType()->getScalarSizeInBits();
> +    const unsigned ShftCnt = ShAmt->getLimitedValue(Width);
> +    const KnownBits YKnown = computeKnownBits(Y, Q.DL, 0, Q.AC, Q.CxtI, Q.DT);
>      const unsigned EffWidthY = Width - YKnown.countMinLeadingZeros();
>      if (EffWidthY <= ShftCnt) {
>        const KnownBits XKnown = computeKnownBits(X, Q.DL, 0, Q.AC, Q.CxtI,
>
>
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