https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114046
Bug ID: 114046
Summary: Aarch64: Os,O1,02,O3 optimisations generates unaligned
access in short members of structure
Product: gcc
Version: 13.2.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: driver
Assignee: unassigned at gcc dot gnu.org
Reporter: stephane at syena dot net
Target Milestone: ---
The issuer is reproduced with the following (simplified) code:
struct test {
short a;
short b;
short c;
};
void function( struct test *p, int n ) {
p->a = n;
p->b = 0;
p->c = 0;
}
# gcc -Os -S unaligned_store.c && cat unaligned_store.s
.arch armv8-a
.file "unaligned_store.c"
.text
.align 2
.global function
.type function, %function
function:
strh w1, [x0]
str wzr, [x0, 2] <<<<<<<<< Alignment fault
ret
.size function, .-function
.ident "GCC: (Arm GNU Toolchain 13.2.rel1 (Build arm-13.7)) 13.2.1
20231009"
The second instruction generates an unaligned 32-bits store at a 16-bits
aligned address.
I suspect that the optimizer detects that consecutive short members b and c are
both set to zero and group them to generate a single long access but somehow
fails to detect that the resulting access is not aligned.
