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PR13326: Fix a subtle edge case in the udiv -> magic multiply generator.

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This caused 6 of 65k possible 8 bit udivs to be wrong.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@160058 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Benjamin Kramer
2012-07-11 18:31:59 +00:00
parent 79137851bf
commit 597f2950d8
2 changed files with 22 additions and 1 deletions
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2
lib/Support/APInt.cpp
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@@ -1446,7 +1446,7 @@ APInt::mu APInt::magicu(unsigned LeadingZeros) const {
APInt signedMin = APInt::getSignedMinValue(d.getBitWidth());
APInt signedMax = APInt::getSignedMaxValue(d.getBitWidth());
nc = allOnes - (-d).urem(d);
nc = allOnes - (allOnes - d).urem(d);
p = d.getBitWidth() - 1; // initialize p
q1 = signedMin.udiv(nc); // initialize q1 = 2p/nc
r1 = signedMin - q1*nc; // initialize r1 = rem(2p,nc)