https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111626
Bug ID: 111626
Summary: missed optimization combining offset of array member
in struct with offset inside the array
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: middle-end
Assignee: unassigned at gcc dot gnu.org
Reporter: lis8215 at gmail dot com
Target Milestone: ---
The simple code:
struct some_struct {
uint32_t some_member;
uint32_t arr[4][16];
};
uint32_t fn(const struct some_struct *arr, int idx)
{
return arr->arr[1][idx];
}
is used to showcase a suboptimal optimization on some platforms including
RISC-V and MIPS (32 & 64 bit) even with `some_member` commented out.
while GCC emits:
addi a1,a1,16
slli a1,a1,2
add a0,a0,a1
lw a0,4(a0)
ret
Clang does better job:
slli a1, a1, 2
add a0, a0, a1
lw a0, 68(a0)
ret
