https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62139
Bug ID: 62139
Summary: Tilera tilepro: useless stack pointer operations
Product: gcc
Version: 4.9.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: jose.parera at upm dot es
I made a C function to split a register into halves and return them as a
struct. The code works fine but adds a couple of useless instructions
concerning the stack that cause a performance penalty.
typedef struct {
uint32_t y0;
uint32_t y1;
} __tpro_split_t;
__tpro_split_t split(uint32_t a) {
__tpro_split_t res = {
.y0 = __insn_srai(__insn_shli(a, 16), 16),
.y1 = __insn_srai(a, 16)
};
return res;
}
The assembler code is
.cfi_startproc
{
shli r10, r0, 16
srai r1, r0, 16
}
{
addi sp, sp, -8 <== useless
.cfi_def_cfa_offset 8
srai r0, r10, 16
}
{
addi sp, sp, 8 <== useless
.cfi_def_cfa_offset 0
jrp lr
}
.cfi_endproc
I think that this issue is quite similar to those at bug #48941 but in this
case for Tilera TilePro architecture, and probably, also TileGx.
