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KnownBits: refine high-bits of mul in signed case #113051

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KnownBits: refine high-bits of mul in signed case #113051

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Commits on Oct 19, 2024

  1. ValueTracking/test: cover known bits of mul

    @artagnon
    artagnon committed Oct 19, 2024
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  2. KnownBits: refine high-bits of mul in signed case 

    KnownBits::mul suffers from the deficiency that it doesn't account for
signed inputs. Fix it by refining known leading zeros when both inputs
are signed, and setting known leading ones when one of the inputs is
signed. The strategy we've used is to still use umul_ov, after adjusting
for signed inputs, and setting known leading ones from the negation of
the result, when it is known to be negative, noting that a possibly-zero
result is a special case.
    @artagnon
    artagnon committed Oct 19, 2024
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