[all-commits] [llvm/llvm-project] 178318: Respect integer overflow handling in abs builtin

[Artem Labazov via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 1783185790de29b24d3850d33d9a9d586e6bbd39
      https://github.com/llvm/llvm-project/commit/1783185790de29b24d3850d33d9a9d586e6bbd39
  Author: Artem Labazov <123321artyom at gmail.com>
  Date:   2023-08-17 (Thu, 17 Aug 2023)

  Changed paths:
    M clang/docs/ReleaseNotes.rst
    M clang/lib/CodeGen/CGBuiltin.cpp
    A clang/test/CodeGen/abs-overflow.c
    A clang/test/ubsan/TestCases/Misc/abs.cpp

  Log Message:
  -----------
  Respect integer overflow handling in abs builtin

Currenly both Clang and GCC support the following set of flags that
control code gen of signed overflow:

* -fwrapv: overflow is defined as in two-complement
* -ftrapv: overflow traps
* -fsanitize=signed-integer-overflow: if undefined (no -fwrapv), then
overflow behaviour is controlled by UBSan runtime, overrides -ftrapv.

However, clang ignores these flags for __builtin_abs(int) and its
higher-width versions, so passing minimum integer value always causes
poison.

The same holds for *abs(), which are not handled in frontend at all but
folded to llvm.abs.* intrinsics during InstCombinePass. The intrinsics
are not instrumented by UBSan, so the functions need special handling
as well.

This patch does a few things:

* Handle *abs() in CGBuiltin the same way as __builtin_*abs()
* -fsanitize=signed-integer-overflow now properly instruments abs() with
UBSan
* -fwrapv and -ftrapv handling for abs() is made consistent with GCC

Fixes https://github.com/llvm/llvm-project/issues/45129
Fixes https://github.com/llvm/llvm-project/issues/45794

Differential Revision: https://reviews.llvm.org/D156821