https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114208
Bug ID: 114208
Summary: DSE deletes a store that is not dead
Product: gcc
Version: 14.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: rtl-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: gjl at gcc dot gnu.org
Target Milestone: ---
Created attachment 57594
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=57594&action=edit
Reduced C test case
$ avr-gcc -mmcu=attiny40 bug-dse.c -S -Os -dp -mfuse-add=3 -fdse
the following C test case:
struct S { char a, b; };
__attribute__((__noinline__,__noclone__))
void test (const struct S *s)
{
if (s->a != 3 || s->b != 4)
__builtin_abort();
}
int main (void)
{
struct S s = { 3, 4 };
test (&s);
return 0;
}
Then with DSE off (-fno-dse), main has a store of 3 into s.a:
main:
...
ldi r20,lo8(3) ; 22 [c=4 l=1] movqi_insn/1
ld __tmp_reg__,Y+ ; 24 [c=4 l=1] *addhi3/3
st Y+,r20 ; 48 [c=4 l=1] movqi_insn/2
ldi r20,lo8(4) ; 27 [c=4 l=1] movqi_insn/1
st Y,r20 ; 30 [c=4 l=1] movqi_insn/2
...
but with DSE on, pass .dse2 removes the first store (insn 48, and in the wake
also insn 22) that sets s.a to 3:
main:
...
ldi r20,lo8(4) ; 27 [c=4 l=1] movqi_insn/1
subi r28,-2 ; 29 [c=4 l=2] *addhi3/3
sbci r29,-1
st Y,r20 ; 30 [c=4 l=1] movqi_insn/2
...
Configured with: ../../source/gcc-master/configure --target=avr --disable-nls
--with-dwarf2 --with-gnu-as --with-gnu-ld --disable-shared
--enable-languages=c,c++
Thread model: single
Supported LTO compression algorithms: zlib
gcc version 14.0.1 20240302 (experimental) (GCC)
