https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113903
Bug ID: 113903
Summary: sched1 should schedule across EBBS
Product: gcc
Version: 14.0
Status: UNCONFIRMED
Keywords: missed-optimization
Severity: normal
Priority: P3
Component: rtl-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: tnfchris at gcc dot gnu.org
Target Milestone: ---
The following testcase:
#define N 306
#define NEEDLE 136
int table[N];
int foo (int i, unsigned short parse_tables_n)
{
parse_tables_n >>= 9;
parse_tables_n += 11;
while (i < N && parse_tables_n--)
table[i++] = 0;
return table[NEEDLE];
}
compiled at -O3 shows an issue we've started getting with the support for early
break vectorization.
sched1 doesn't seem to be able to schedule across EBBs, which is logical since
we never really needed to before.
However the above code generates:
.L10:
st1w z28.s, p7, [x1, #1, mul vl]
st1w z28.s, p7, [x1]
add x1, x1, x5
cmp w0, w2
bcc .L17
.L8:
cmpne p15.h, p7/z, z31.h, #0
mov z29.d, z31.d
not p15.b, p14/z, p15.b
mov z27.d, z30.d
add w2, w2, w4
dech z31.h
ptest p14, p15.b
incw z30.s, all, mul #2
b.none .L10
umov w1, v29.h[0]
umov w20, v27.s[0]
and w3, w1, 65535
b .L6
and the AArch64 codegen inefficiencies aside (which I will tackle myself) shows
that we're copying the old value of the induction variables in every loop
iteration to keep them for the reductions if we exit.
However the new values are not live in L8 and so the operations can be moved to
L10:
.L10:
incw z30.s, all, mul #2
dech z31.h
st1w z28.s, p7, [x1, #1, mul vl]
st1w z28.s, p7, [x1]
add x1, x1, x5
cmp w0, w2
bcc .L17
.L8:
cmpne p15.h, p7/z, z31.h, #0
not p15.b, p14/z, p15.b
add w2, w2, w4
ptest p14, p15.b
b.none .L10
umov w1, v31.h[0]
umov w20, v30.s[0]
and w3, w1, 65535
b .L6
and thus decreasing the live ranges. The optimal codegen for this sequence is:
.L10:
dech z31.h
incw z30.s, all, mul #2
st1w z28.s, p7, [x1, #1, mul vl]
st1w z28.s, p7, [x1]
add x1, x1, x5
cmp w0, w2
bcc .L17
.L8:
cmpeq p15.h, p7/z, z31.h, #0
add w2, w2, w4
b.none .L10
umov w1, v31.h[0]
umov w20, v30.s[0]
b .L6
