https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107548
Bug ID: 107548
Summary: STV doesn't consider vec_select
Product: gcc
Version: 13.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: rguenth at gcc dot gnu.org
Target Milestone: ---
typedef unsigned int v4si __attribute__((vector_size(16)));
unsigned f (v4si a, v4si b)
{
a[0] += b[0];
return a[0] + a[1];
}
gets optimized to
f:
.LFB0:
.cfi_startproc
vpextrd $1, %xmm0, %edx
vmovd %xmm0, %eax
addl %edx, %eax
vmovd %xmm1, %edx
addl %edx, %eax
ret
with znver2 arch, but similar with others while it seems to be beneficial
to shuffle a[1] to a'[0] and perform the add on the vector side eliding
two xmm->gpr moves. STV2 sees
19: r94:V4SI=xmm0:V4SI
REG_DEAD xmm0:V4SI
2: r87:V4SI=r94:V4SI
REG_DEAD r94:V4SI
20: r95:V4SI=xmm1:V4SI
REG_DEAD xmm1:V4SI
3: NOTE_INSN_DELETED
4: NOTE_INSN_FUNCTION_BEG
7: r90:SI=vec_select(r87:V4SI,parallel)
8: r91:SI=vec_select(r87:V4SI,parallel)
REG_DEAD r87:V4SI
9: {r92:SI=r90:SI+r91:SI;clobber flags:CC;}
REG_DEAD r91:SI
REG_DEAD r90:SI
REG_UNUSED flags:CC
10: r93:SI=vec_select(r95:V4SI,parallel)
REG_DEAD r95:V4SI
11: {r89:SI=r92:SI+r93:SI;clobber flags:CC;}
REG_DEAD r93:SI
REG_DEAD r92:SI
REG_UNUSED flags:CC
16: ax:SI=r89:SI
REG_DEAD r89:SI
17: use ax:SI
but it lacks vec_select support:
Created a new instruction chain #1
Building chain #1...
Adding insn 9 to chain #1
Adding insn 11 into chain's #1 queue
r90 def in insn 7 isn't convertible
Mark r90 def in insn 7 as requiring both modes in chain #1
r91 def in insn 8 isn't convertible
Mark r91 def in insn 8 as requiring both modes in chain #1
Adding insn 11 to chain #1
r89 use in insn 16 isn't convertible
Mark r89 def in insn 11 as requiring both modes in chain #1
r93 def in insn 10 isn't convertible
Mark r93 def in insn 10 as requiring both modes in chain #1
Collected chain #1...
insns: 9, 11
defs to convert: r89, r90, r91, r93
Computing gain for chain #1...
Instruction conversion gain: 0
Registers conversion cost: 24
Total gain: -24
Chain #1 conversion is not profitable
