[PATCH] D34121: [ubsan] Teach the pointer overflow check that "p - <unsigned> <= p" (PR33430)

[Vedant Kumar via Phabricator via cfe-commits]

vsk created this revision.

The pointer overflow check gives false negatives when dealing with
expressions in which an unsigned value is subtracted from a pointer.
This is summarized in PR33430 [1]: ubsan permits the result of the
submission to be greater than "p", but it should not.

To fix the issue, we should track whether or not the pointer expression
is a subtraction. If it is, and the indices are unsigned, we know to
expect "p - <unsigned> <= p".

I've tested this by running check-{llvm,clang} with a stage2 ubsan-enabled build. I've also added some tests to compiler-rt, which I'll upload in a separate patch.

[1] https://bugs.llvm.org/show_bug.cgi?id=33430


https://reviews.llvm.org/D34121

Files:
  lib/CodeGen/CGExpr.cpp
  lib/CodeGen/CGExprScalar.cpp
  lib/CodeGen/CodeGenFunction.h
  test/CodeGen/ubsan-pointer-overflow.m

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