https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112776
Bug ID: 112776
Summary: RISC-V Regression: Missed optimization of VSETVL PASS
Product: gcc
Version: 14.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: juzhe.zhong at rivai dot ai
Target Milestone: ---
#include "riscv_vector.h"
void
foo_vec(float *r, const float *x)
{
int i, k;
vfloat32m4_t x_vec;
vfloat32m4_t x_forward_vec;
vfloat32m4_t temp_vec;
/**
* I have to use m1 to complicat intrisic
*/
vfloat32m1_t dst_vec;
vfloat32m1_t src_vec;
float result = 0.0f;
float shift_prev = 0.0f;
size_t n = 64;
for(size_t vl; n>0; n -=vl){
vl = __riscv_vsetvl_e32m4(n); //LMUL=4
x_vec = __riscv_vle32_v_f32m4(&x[0], vl);
x_forward_vec = __riscv_vle32_v_f32m4(&x[0], vl);
temp_vec = __riscv_vfmul_vv_f32m4(x_vec, x_forward_vec, vl);
/**
* I have to use m1 to complicat intrisic
*/
//vfloat32m1_t __riscv_vfmv_s_tu(vfloat32m1_t vd, float rs1, size_t vl);
src_vec = __riscv_vfmv_s_tu(src_vec, 0.0f, vl); //initial
src_vec
//dst_vec = __riscv_vfmv_s_f_f32m1_tu(dst_vec, 0.0f, vl); //clean
for vfredosum
dst_vec = __riscv_vfmv_s_tu(dst_vec, 0.0f, vl); //clean for
vfredosum
dst_vec = __riscv_vfredosum_tu(dst_vec, temp_vec, src_vec, vl);
r[0] = __riscv_vfmv_f_s_f32m1_f32(dst_vec);
}
}
ASM:
GCC-14 foo_vec:
li a4,64
.L2:
vsetvli a5,a4,e8,m1,ta,ma --->
vsetvli zero,a5,e32,m1,tu,ma
vmv.s.x v2,zero
vmv.s.x v1,zero
vsetvli zero,a5,e32,m4,tu,ma
vle32.v v4,0(a1)
vfmul.vv v4,v4,v4
vfredosum.vs v1,v4,v2
vfmv.f.s fa5,v1
fsw fa5,0(a0)
sub a4,a4,a5
bne a4,zero,.L2
ret
GCC-13:
foo_vec(float*, float const*):
fmv.s.x fa5,zero
li a4,64
.L2:
vsetvli a5,a4,e32,m4,ta,ma
vle32.v v28,0(a1)
vfmv.s.f v25,fa5
vfmul.vv v28,v28,v28
vfmv.s.f v24,fa5
sub a4,a4,a5
vfredosum.vs v24,v28,v25
vfmv.f.s fa4,v24
fsw fa4,0(a0)
bne a4,zero,.L2
ret
