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
Howerver, 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#45129 and #45794
Reviewed By: efriedma, MaskRay
Differential Revision: https://reviews.llvm.org/D156821
This reverts commit 1783185790de29b24d3850d33d9a9d586e6bbd39,
which broke the buildbots, starting with when it was first built in https://lab.llvm.org/buildbot/#/builders/85/builds/18390
(N.B. I think the patch is uncovering real bugs; the revert
is simply to keep the tree green and the buildbots useful, because I'm not confident how to
fix-forward all the found bugs.)
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
