https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117031
--- Comment #5 from Richard Biener <rguenth at gcc dot gnu.org> ---
For example
void
test3 (unsigned short *x, double *y, int n)
{
for (int i = 0; i < n; i+=1)
{
unsigned short a1 = x[i * 4 + 0];
unsigned short b1 = x[i * 4 + 1];
unsigned short c1 = x[i * 4 + 2];
unsigned short d1 = x[i * 4 + 3];
y[i+0] = (double)(a1 + b1 + c1 + d1);
}
}
ends up
.L4:
ld4 {v28.8h - v31.8h}, [x4], 64
add x3, x3, 64
uaddl2 v26.4s, v28.8h, v29.8h
uaddl v28.4s, v28.4h, v29.4h
uaddw2 v0.4s, v26.4s, v30.8h
uaddw v28.4s, v28.4s, v30.4h
uaddw2 v0.4s, v0.4s, v31.8h
uaddw v28.4s, v28.4s, v31.4h
sxtl v1.2d, v0.2s
sxtl v27.2d, v28.2s
sxtl2 v0.2d, v0.4s
sxtl2 v28.2d, v28.4s
scvtf v1.2d, v1.2d
scvtf v27.2d, v27.2d
scvtf v0.2d, v0.2d
scvtf v28.2d, v28.2d
stp q1, q0, [x3, -32]
stp q27, q28, [x3, -64]
cmp x5, x4
bne .L4
we can now use widening plus and avoid the HI -> DF conversion penalty.
You can see that with ld4 there's no permutes needed at all.
