https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95254
Bug ID: 95254
Summary: aarch64: gcc generate inefficient code with fixed sve
vector length
Product: gcc
Version: 11.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: felix.yang at huawei dot com
Target Milestone: ---
Target: aarch64
Test case:
typedef short __attribute__((vector_size (8))) v4hi;
typedef union U4HI { v4hi v; short a[4]; } u4hi;
short b[4];
void pass_v4hi (v4hi v)
{
int i;
u4hi u;
u.v = v;
for (i = 0; i < 4; i++)
b[i] = u.a[i];
};
$ gcc -O2 -ftree-slp-vectorize -S -march=armv8.2-a+sve foo.c
assembly code:
pass_v4hi:
.LFB0:
.cfi_startproc
adrp x0, .LANCHOR0
str d0, [x0, #:lo12:.LANCHOR0]
ret
.cfi_endproc
$ gcc -O2 -ftree-slp-vectorize -S -march=armv8.2-a+sve -msve-vector-bits=256
foo.c
assembly code:
pass_v4hi:
.LFB0:
.cfi_startproc
sub sp, sp, #16
.cfi_def_cfa_offset 16
ptrue p0.b, vl32
adrp x0, .LANCHOR0
add x0, x0, :lo12:.LANCHOR0
str d0, [sp, 8]
ld1h z0.d, p0/z, [sp, #1, mul vl]
st1h z0.d, p0, [x0]
add sp, sp, 16
.cfi_def_cfa_offset 0
ret
.cfi_endproc
The root cause here is that we choose a different mode in
aarch64_vectorize_related_mode[1]: VNx2HImode instead of V4HImode.
Then in the final tree ssa forwprop pass, we need to do a VIEW_CONVERT from
V4HImode to VNx2HImode.
One way to fix this is to catch and simplify the pattern in
aarch64_expand_sve_mem_move, emitting a mov pattern of V4HImode instead.
I am assuming endianness does not make a difference here. Will propose a patch
for comments.
[1] call trace:
(gdb) bt
#0 aarch64_vectorize_related_mode (vector_mode=E_VNx8HImode, element_mode=...,
nunits=...) at ../../gcc-git/gcc/config/aarch64/aarch64.c:2377
#1 0x00000000012983b4 in related_vector_mode (vector_mode=E_VNx8HImode,
element_mode=..., nunits=...) at ../../gcc-git/gcc/stor-layout.c:535
#2 0x0000000001652918 in get_related_vectype_for_scalar_type
(prevailing_mode=E_VNx8HImode, scalar_type=0xffffb22da498, nunits=...)
at ../../gcc-git/gcc/tree-vect-stmts.c:11463
#3 0x0000000001653304 in get_vectype_for_scalar_type (vinfo=0x2f0dc80,
scalar_type=0xffffb22da498, group_size=4)
at ../../gcc-git/gcc/tree-vect-stmts.c:11545
#4 0x00000000016533a0 in get_vectype_for_scalar_type (vinfo=0x2f0dc80,
scalar_type=0xffffb22da498, node=0x2e5d460)
at ../../gcc-git/gcc/tree-vect-stmts.c:11569
#5 0x00000000016987e8 in vect_get_constant_vectors (vinfo=0x2f0dc80,
slp_node=0x2e53080, op_num=0, vec_oprnds=0xffffffffc738)
at ../../gcc-git/gcc/tree-vect-slp.c:3562
#6 0x00000000016993f8 in vect_get_slp_defs (vinfo=0x2f0dc80,
slp_node=0x2e53080, vec_oprnds=0xffffffffc7a8, n=1) at
../../gcc-git/gcc/tree-vect-slp.c:3786
#7 0x0000000001631c70 in vect_get_vec_defs (vinfo=0x2f0dc80,
op0=0xffffb20e3120, op1=0x0, stmt_info=0x2feef60, vec_oprnds0=0xffffffffcdd0,
vec_oprnds1=0x0,
slp_node=0x2e53080) at ../../gcc-git/gcc/tree-vect-stmts.c:1726
#8 0x0000000001648bc8 in vectorizable_store (vinfo=0x2f0dc80,
stmt_info=0x2feef60, gsi=0xffffffffdad0, vec_stmt=0xffffffffd5b0,
slp_node=0x2e53080,
cost_vec=0x0) at ../../gcc-git/gcc/tree-vect-stmts.c:8186
#9 0x0000000001651808 in vect_transform_stmt (vinfo=0x2f0dc80,
stmt_info=0x2feef60, gsi=0xffffffffdad0, slp_node=0x2e53080,
slp_node_instance=0x2fefe70)
at ../../gcc-git/gcc/tree-vect-stmts.c:11184
#10 0x000000000169a4a0 in vect_schedule_slp_instance (vinfo=0x2f0dc80,
node=0x2e53080, instance=0x2fefe70) at ../../gcc-git/gcc/tree-vect-slp.c:4134
#11 0x000000000169aaac in vect_schedule_slp (vinfo=0x2f0dc80) at
../../gcc-git/gcc/tree-vect-slp.c:4258
#12 0x00000000016972f0 in vect_slp_bb_region (region_begin=..., region_end=...,
datarefs=..., n_stmts=10) at ../../gcc-git/gcc/tree-vect-slp.c:3227
#13 0x0000000001697c60 in vect_slp_bb (bb=0xffffb22ce340) at
../../gcc-git/gcc/tree-vect-slp.c:3350
#14 0x00000000016a56f0 in (anonymous namespace)::pass_slp_vectorize::execute
(this=0x2e6aae0, fun=0xffffb2116000) at
../../gcc-git/gcc/tree-vectorizer.c:1320
