https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109399
Bug ID: 109399
Summary: RISC-V: RVV VSETVL PASS backward demand fusiton bug
Product: gcc
Version: 13.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: juzhe.zhong at rivai dot ai
Target Milestone: ---
Consider this following case:
#include "riscv_vector.h"
void foo(void *in1, void *in2, void *in3, void *out, size_t n) {
size_t vl = __riscv_vsetvlmax_e32m1();
vint32m1_t a = __riscv_vle32_v_i32m1(in1, vl);
vint32m1_t b = __riscv_vle32_v_i32m1_tu(a, in2, vl);
vint32m1_t c = __riscv_vle32_v_i32m1_tu(b, in3, vl);
__riscv_vse32_v_i32m1(out, c, vl);
}
Current codegen:
foo:
vsetvli a5,zero,e32,m1,ta,mu
vle32.v v1,0(a0)
vle32.v v1,0(a1)
vle32.v v1,0(a2)
vse32.v v1,0(a3)
ret
It's obvious that "ta,mu" is incorrect. Instead, we should emit vsetvl
with "tu,m[au]" ,mask policy can be either mu or ma. But tail policy must be
"tu".
The reason we have this issue is that we didn't update && change user vsetvl
instruction during local backward demand fusion (Phase 1).
Will post a bug fix patch soon.
