https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115995
Bug ID: 115995
Summary: RISC-V: Can't generate portable RVV code for
rv64gcv_zvl512b
Product: gcc
Version: 15.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: sh.chiang04 at gmail dot com
CC: juzhe.zhong at rivai dot ai, kito at gcc dot gnu.org,
pan2.li at intel dot com, rdapp at gcc dot gnu.org
Target Milestone: ---
Created attachment 58704
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=58704&action=edit
same as gcc.c-torture/execute/990128-1.c
The fail test is from gcc.c-torture/execute/990128-1.c in main(), and it's for
testing link list. The following loop split 2 parts, one for main loop, another
for tail, if -march=rv64gcv_zvl512b.
According Vector spec for constraints on setting VL.
The rule 2: ceil(AVL / 2) ≤ vl ≤ VLMAX if AVL < (2 * VLMAX)
Such as, vsetivli a2,10,e64,m1,ta,ma (VLEN = 512, SEW=64, LMUL=1, VLMAX=8,
AVL=10). Follow rule 2, the VL range is 5 ≤ vl ≤ 8.
https://github.com/riscv/riscv-v-spec/blob/master/v-spec.adoc#63-constraints-on-setting-vl
This case main loop expected VL to be 8, and tail VL to be 2, but spec says VL
may is 5 to 8. The fail occurred when VL was 5, The link list has not been
completely created.
compile option: -march=rv64gcv_zvl512b1p0 -mabi=lp64d -O2
#define MAX 10
int
main(void)
{
struct s *pp;
struct s *next;
int i;
p = &ss;
next = p;
for ( i = 0; i < MAX; i++ ) {
next->n = &sss[i];
next = next->n;
}
next->n = 0;
...
}
main:
vsetvli a1,zero,e32,mf2,ta,ma
lui a5,%hi(ss)
vid.v v5
addi a5,a5,%lo(ss)
vsetvli zero,zero,e64,m1,ta,ma
lui a3,%hi(.LANCHOR0)
vmv.v.x v2,a5
addi a3,a3,%lo(.LANCHOR0)
csrr a5,vlenb
vsext.vf2 v1,v5
vmv.v.x v3,a3
vmv.v.i v4,8
srli a5,a5,3
addi a5,a5,-1
vslidedown.vx v2,v2,a5
vmadd.vv v1,v4,v3
lui a0,%hi(ss)
vmv.x.s a4,v2
vsetivli a2,10,e64,m1,ta,ma. // VL= 5 to 8
vslide1up.vx v2,v1,a4
addi sp,sp,-32
lui a4,%hi(p)
addi a6,a0,%lo(ss)
sd a6,%lo(p)(a4)
sd ra,24(sp)
vsuxei64.v v1,(zero),v2. // create link list
li a4,10
sub a4,a4,a2 // a4 = 10 - (2 to 5)
bne a4,zero,.L22
.L16:
....
.L22:
vsetvli a4,a4,e32,mf2,ta,ma // a4 = (5 to 8)
vmv.v.x v2,a2
vsetvli a1,zero,e64,m1,ta,ma
vslidedown.vx v1,v1,a5
vsetvli zero,a4,e32,mf2,ta,ma
vadd.vv v2,v2,v5
vsetvli zero,zero,e64,m1,ta,ma
vmv.x.s a5,v1
vsext.vf2 v1,v2
vmadd.vv v1,v4,v3
vslide1up.vx v2,v1,a5
vsuxei64.v v1,(zero),v2. // create link list
j .L16
Following information is from QEMU. Ａ link list is missing to create (0x12a68).
Run for VL=8
0x12a40 <sss>: 0x00012a48 0x00000000 0x00012a50 0x00000000
0x12a50 <sss+16>: 0x00012a58 0x00000000 0x00012a60 0x00000000
0x12a60 <sss+32>: 0x00012a68 0x00000000 0x00012a70 0x00000000
0x12a70 <sss+48>: 0x00012a78 0x00000000 0x00012a80 0x00000000
0x12a80 <sss+64>: 0x00012a88 0x00000000 0x00000000 0x00000000
Run for VL=5
0x12a40 <sss>: 0x00012a48 0x00000000 0x00012a50 0x00000000
0x12a50 <sss+16>: 0x00012a58 0x00000000 0x00012a60 0x00000000
0x12a60 <sss+32>: 0x00000000 0x00000000 0x00012a70 0x00000000
0x12a70 <sss+48>: 0x00012a78 0x00000000 0x00012a80 0x00000000
0x12a80 <sss+64>: 0x00012a88 0x00000000 0x00000000 0x00000000
