The function is a no-op if 'vta' is zero but we're still doing a lot of
stuff in this function regardless. vext_set_elems_1s() will ignore every
single time (since vta is zero) and we just wasted time.
Skip it altogether in this case. Aside from the code simplification
there's a noticeable emulation performance gain by doing it. For a
regular C binary that does a vectors operation like this:
=======
#define SZ 10000000
int main ()
{
int *a = malloc (SZ * sizeof (int));
int *b = malloc (SZ * sizeof (int));
int *c = malloc (SZ * sizeof (int));
for (int i = 0; i < SZ; i++)
c[i] = a[i] + b[i];
return c[SZ - 1];
}
=======
Emulating it with qemu-riscv64 and RVV takes ~0.3 sec:
$ time ~/work/qemu/build/qemu-riscv64 \
-cpu rv64,debug=false,vext_spec=v1.0,v=true,vlen=128 ./foo.out
real 0m0.303s
user 0m0.281s
sys 0m0.023s
With this skip we take ~0.275 sec:
$ time ~/work/qemu/build/qemu-riscv64 \
-cpu rv64,debug=false,vext_spec=v1.0,v=true,vlen=128 ./foo.out
real 0m0.274s
user 0m0.252s
sys 0m0.019s
This performance gain adds up fast when executing heavy benchmarks like
SPEC.
Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Acked-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Palmer Dabbelt <palmer@rivosinc.com>
Reviewed-by: Weiwei Li <liweiwei@iscas.ac.cn>
Message-Id: <20230427205708.246679-2-dbarboza@ventanamicro.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
Daniel Henrique Barboza
bc0ec52eb2