RISC-V: Make liveness estimation be aware of .vi variant
Consider this following case:
void
f (int *restrict a, int *restrict b, int *restrict c, int *restrict d, int n)
{
for (int i = 0; i < n; i++)
{
int tmp = b[i] + 15;
int tmp2 = tmp + b[i];
c[i] = tmp2 + b[i];
d[i] = tmp + tmp2 + b[i];
}
}
Current dynamic LMUL cost model choose LMUL = 4 because we count the "15" as
consuming 1 vector register group which is not accurate.
We teach the dynamic LMUL cost model be aware of the potential vi variant instructions
transformation, so that we can choose LMUL = 8 according to more accurate cost model.