https://gcc.gnu.org/bugzilla/show_bug.cgi?id=127638
Bug ID: 127638
Summary: bitintlower increases alignment requirements
Product: gcc
Version: 17.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: kristerw at gcc dot gnu.org
Blocks: 118443
Target Milestone: ---
bitintlower incorrectly increases alignment requirements when compiling the
function below for x86_64 with -O2:
void
foo (void *p, _BitInt(246) x)
{
__builtin_memcpy (p, &x, sizeof x);
}
bitintlower transforms this into four 64-bit load/store instructions:
_5 = MEM <unsigned long> [(_BitInt(246) *)&x];
MEM <unsigned long> [(char * {ref-all})p_3(D)] = _5;
_6 = MEM <unsigned long> [(_BitInt(246) *)&x + 8B];
MEM <unsigned long> [(char * {ref-all})p_3(D) + 8B] = _6;
...
The stores require 8-byte alignment, which is incorrect because p may be
unaligned.
Referenced Bugs:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=118443
[Bug 118443] [Meta bug] Bugs triggered by and blocking more smtgcc testing
