[PATCH] D34590: [ubsan] Diagnose invalid uses of builtins (clang)

[Vedant Kumar via Phabricator via cfe-commits]

vsk created this revision.

On some targets, passing zero to the clz() or ctz() builtins has
undefined behavior. I ran into this issue while debugging UB in
__hash_table from libcxx: the bug I was seeing manifested itself
differently under -O0 vs -Os, due to a UB call to clz() (see:
libcxx/r304617).

This patch introduces a check which can detect UB calls to builtins.

llvm.org/PR26979


https://reviews.llvm.org/D34590

Files:
  docs/UndefinedBehaviorSanitizer.rst
  include/clang/Basic/Sanitizers.def
  lib/CodeGen/CGBuiltin.cpp
  lib/CodeGen/CodeGenFunction.h
  test/CodeGen/ubsan-builtin-checks.c
  test/Driver/fsanitize.c

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