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Pull in r293773 from upstream llvm trunk (by Sanjay Patel):

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[ValueTracking] avoid crashing from bad assumptions (PR31809)

  A program may contain llvm.assume info that disagrees with other
  analysis. This may be caused by UB in the program, so we must not
  crash because of that.

  As noted in the code comments:
  https://llvm.org/bugs/show_bug.cgi?id=31809
  ...we can do better, but this at least avoids the assert/crash in the
  bug report.

  Differential Revision: https://reviews.llvm.org/D29395

This fixes an assertion when building editors/emacs-devel.

PR:		216614
This commit is contained in:
Dimitry Andric 2017-02-02 23:01:29 +00:00
parent 077e1117dc
commit c819c1240d
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/projects/clang400-import/; revision=313110
1 changed files with 17 additions and 0 deletions
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17
contrib/llvm/lib/Analysis/ValueTracking.cpp
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@ -781,6 +781,23 @@ static void computeKnownBitsFromAssume(const Value *V, APInt &KnownZero,
APInt::getHighBitsSet(BitWidth, RHSKnownZero.countLeadingOnes());
}
}
// If assumptions conflict with each other or previous known bits, then we
// have a logical fallacy. This should only happen when a program has
// undefined behavior. We can't assert/crash, so clear out the known bits and
// hope for the best.
// FIXME: Publish a warning/remark that we have encountered UB or the compiler
// is broken.
// FIXME: Implement a stronger version of "I give up" by invalidating/clearing
// the assumption cache. This should indicate that the cache is corrupted so
// future callers will not waste time repopulating it with faulty assumptions.
if ((KnownZero & KnownOne) != 0) {
KnownZero.clearAllBits();
KnownOne.clearAllBits();
}
}
// Compute known bits from a shift operator, including those with a