https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114180
Bug ID: 114180
Summary: RISC-V: missing vsetvl changes tail policy and causes
wrong codegen
Product: gcc
Version: 13.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: camel-cdr at protonmail dot com
Target Milestone: ---
There is a codegen bug for RVV intrinsics in gcc 13.2.0, tested on native
hardware and cross-compilers.
It's fixed in on trunk, but I'm not sure how your policies on back-porting
fixes is.
I wasn't able to find an existing bug report that matches the bug, but I think
this patch might be the one that fixed it in trunk:
https://gcc.gnu.org/pipermail/gcc-patches/2024-January/643934.html
Reproduction:
$ cat test.c
#include <riscv_vector.h>
int validate_ascii(const char *buf, size_t len) {
size_t vlmax = __riscv_vsetvlmax_e8m8();
vint8m8_t mask = __riscv_vmv_v_x_i8m8(0, vlmax);
for (size_t vl; len > 0; len -= vl, buf += vl) {
vl = __riscv_vsetvl_e8m8(len);
vint8m8_t v = __riscv_vle8_v_i8m8((int8_t*)buf, vl);
mask = __riscv_vor_vv_i8m8_tu(mask, mask, v, vl);
}
return __riscv_vfirst_m_b1(__riscv_vmslt_vx_i8m8_b1(mask, 0, vlmax), vlmax) <
0;
}
$ gcc-13 -march=rv64gcv -O2 -S test.c
$ cat test.s
validate_ascii:
vsetvli a4,zero,e8,m8,ta,ma
vmv.v.i v24,0
beq a1,zero,.L2
.L3:
vsetvli a5,a1,e8,m8,ta,ma # <--- should be tu,ma
sub a1,a1,a5
vle8.v v8,0(a0)
add a0,a0,a5
vor.vv v24,v24,v8
bne a1,zero,.L3
vsetvli a4,zero,e8,m8,ta,ma
.L2:
vmslt.vi v8,v24,0
vfirst.m a0,v8
srli a0,a0,63
ret
(output slightly cleaned up, and annotated)
See also, for online reproduction: https://godbolt.org/z/jsbT4dErs
