[PATCH] D86000: Add an unsigned shift base sanitizer

[JF Bastien via Phabricator via cfe-commits]

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It's not undefined behavior for an unsigned left shift to overflow (i.e. to
shift bits out), but it has been the source of bugs and exploits in certain
codebases in the past. As we do in other parts of UBSan, this patch adds a
dynamic checker which acts beyond UBSan and checks other sources of errors. The
option is enabled completely separately from other checkers since it's unlikely
that folks who have currently adopted other checkers will want this one.

The flag is named: -fsanitize=unsigned-shift-base
This matches shift-base and shift-exponent flags.

rdar://problem/46129047


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D86000

Files:
  clang/docs/UndefinedBehaviorSanitizer.rst
  clang/include/clang/Basic/Sanitizers.def
  clang/lib/CodeGen/CGExprScalar.cpp
  clang/lib/Driver/SanitizerArgs.cpp
  clang/lib/Driver/ToolChain.cpp
  clang/test/CodeGen/unsigned-shift-base.c
  clang/test/Driver/fsanitize.c
  compiler-rt/test/ubsan/TestCases/Integer/unsigned-shift.cpp

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