https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115629
--- Comment #4 from Tamar Christina <tnfchris at gcc dot gnu.org> ---
(In reply to Richard Biener from comment #3)
> So we now tail-merge the two b[i] loading blocks. Can you check SVE
> code-gen with this? If that fixes the PR consider adding a SVE testcase.
Thanks, the codegen is much better now, but shows some other missing mask
tracking in the vectorizer.
Atm we generate:
.L3:
ld1w z31.s, p6/z, [x0, x6, lsl 2] <-- load a
cmpeq p7.s, p6/z, z31.s, #0 <-- a == 0, !a
ld1w z0.s, p7/z, [x2, x6, lsl 2] <-- load c conditionally on !a
cmpeq p7.s, p7/z, z0.s, #0 <-- !a && !c
orr z0.d, z31.d, z0.d <-- a || c
ld1w z29.s, p7/z, [x3, x6, lsl 2] <--- load d where !a && !c
cmpne p5.s, p6/z, z0.s, #0 <--- (a || c) & loop_mask
and p7.b, p6/z, p7.b, p7.b <--- ((!a && !c) && (!a && !c)) &
loop_mask
ld1w z30.s, p5/z, [x1, x6, lsl 2] <-- load b conditionally on (a ||
c)
sel z30.s, p7, z29.s, z30.s <-- select (!a && !c, d, b)
st1w z30.s, p6, [x4, x6, lsl 2]
add x6, x6, x7
whilelo p6.s, w6, w5
b.any .L3
which corresponds to:
# loop_mask_63 = PHI <next_mask_95(10), max_mask_94(20)>
vect__4.10_64 = .MASK_LOAD (vectp_a.8_53, 32B, loop_mask_63);
mask__31.11_66 = vect__4.10_64 != { 0, ... };
mask__56.12_67 = ~mask__31.11_66;
vec_mask_and_70 = mask__56.12_67 & loop_mask_63;
vect__7.15_71 = .MASK_LOAD (vectp_c.13_68, 32B, vec_mask_and_70);
mask__22.16_73 = vect__7.15_71 == { 0, ... };
mask__34.17_75 = vec_mask_and_70 & mask__22.16_73;
vect_iftmp.20_78 = .MASK_LOAD (vectp_d.18_76, 32B, mask__34.17_75);
vect__61.21_79 = vect__4.10_64 | vect__7.15_71;
mask__35.22_81 = vect__61.21_79 != { 0, ... };
vec_mask_and_84 = mask__35.22_81 & loop_mask_63;
vect_iftmp.25_85 = .MASK_LOAD (vectp_b.23_82, 32B, vec_mask_and_84);
_86 = mask__34.17_75 & loop_mask_63;
vect_iftmp.26_87 = VEC_COND_EXPR <_86, vect_iftmp.20_78, vect_iftmp.25_85>;
.MASK_STORE (vectp_res.27_88, 32B, loop_mask_63, vect_iftmp.26_87);
it looks like what's missing is that the mask tracking doesn't know that other
masked operations naturally perform an AND when combined. We do some of this
in the backend but I feel like it may be better to do it in the vectorizer.
In this case, the second load is conditional on the first load mask, which
means it's already done an AND.
And crucially inverting it means you also inverted both conditions.
So there are some superflous masking operations happening. But I guess that's
a separate bug. Shall I just add some tests here and close it and open a new
PR?
