https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114469
Bug ID: 114469
Summary: gcc.dg/torture/bitint-64.c failure with -O2 -flto
-std=c23 -fwrapv
Product: gcc
Version: 14.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: jakub at gcc dot gnu.org
Target Milestone: ---
This test fails with
make check-gcc GCC_TEST_RUN_EXPENSIVE=1
RUNTESTFLAGS="dg-torture.exp=bitint-64.c"
FAIL: gcc.dg/torture/bitint-64.c -O2 -flto -fuse-linker-plugin
-fno-fat-lto-objects execution test
The question is if _Atomic _BitInt(5) should be in memory always sign extended,
or as the ABI says the upper bits are unspecified.
If the former, then I'd say the problem is on the
/* Strip inner integral conversions that do not change precision or size, or
zero-extend while keeping the same size (for bool-to-char). */
(simplify
(view_convert (convert@0 @1))
(if ((INTEGRAL_TYPE_P (TREE_TYPE (@0)) || POINTER_TYPE_P (TREE_TYPE (@0)))
&& (INTEGRAL_TYPE_P (TREE_TYPE (@1)) || POINTER_TYPE_P (TREE_TYPE (@1)))
&& TYPE_SIZE (TREE_TYPE (@0)) == TYPE_SIZE (TREE_TYPE (@1))
&& (TYPE_PRECISION (TREE_TYPE (@0)) == TYPE_PRECISION (TREE_TYPE (@1))
|| (TYPE_PRECISION (TREE_TYPE (@0)) > TYPE_PRECISION (TREE_TYPE
(@1))
&& TYPE_UNSIGNED (TREE_TYPE (@1)))))
(view_convert @1)))
match.pd simplification which transforms
_5 = (unsigned _BitInt(5)) _4;
_7 = (unsigned _BitInt(5)) e.0_1;
_8 = _5 + _7;
_9 = (_BitInt(5)) _8;
_10 = VIEW_CONVERT_EXPR<unsigned char>(_9);
to just
_5 = (unsigned _BitInt(5)) _4;
_7 = (unsigned _BitInt(5)) e.0_1;
_8 = _5 + _7;
_10 = VIEW_CONVERT_EXPR<unsigned char>(_8);
so it is no longer sign extended in the unsigned char.
If the upper bits are undefined as the psABI on x86 says, then perhaps the
VIEW_CONVERT_EXPR emitted by c-common.cc (resolve_overloaded_builtin) is the
culprit:
_13 = __atomic_load_1 (&b, 5);
_14 = VIEW_CONVERT_EXPR<_BitInt(5)>(_13);
and we should change that
/* Cast function result from I{1,2,4,8,16} to the required type.
*/
result = build1 (VIEW_CONVERT_EXPR, TREE_TYPE (new_return),
result);
to something like if (INTEGRAL_TYPE_P (TREE_TYPE (new_return))IINTEGRAL_TYPE_P
(TREE_TYPE (new_return))NTEGRAL_TYPE_P (TREE_TYPE (new_return)))
if (INTEGRAL_TYPE_P (TREE_TYPE (new_return)))
result = fold_convert (TREE_TYPE (new_return), result);
else
result = build1 (VIEW_CONVERT_EXPR, TREE_TYPE (new_return),
result);
Joseph, thoughts on this?
