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rbyd-rr: Explicitly deduplicated diverging conditions

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I'm not really sure why the compiler isn't taking care of this for us.

Usually I prefer duplicated logic over more variables since it means
less state to keep track of when reading/debugging, and the compiler
will optimize it away anyways. But I guess these conditions are just too
complicated in this case?

Maybe the compiler is trying to take advantage of &&/|| short-circuiting
even with -Os?

Even marking the lfsr_tag_diverging* functions with
__attribute__((noinline, pure, const)) doesn't help...

Oh well, this is a case where we can just make the deduplication
explicit for a bit of code savings:

           code          stack
  before: 34176           2864
  after:  34080 (-0.3%)   2864 (+0.0%)

                     code          frame          stack
  appendattr before: 2162            208            560
  appendattr after:  2104 (-2.7%)    216 (+3.8%)    568 (+1.4%)
This commit is contained in:
Christopher Haster
2024-04-15 01:45:22 -05:00
parent 94eb672315
commit 77c45827e5
1 changed files with 17 additions and 34 deletions
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lfs.c
+17 -34
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@@ -2935,38 +2935,28 @@ trunk:;
}
// do bounds want to take different paths? begin diverging
bool diverging = lfsr_tag_diverging2(
alt, weight,
p[0].alt, p[0].weight,
lower_rid, upper_rid,
a_rid, a_tag,
b_rid, b_tag);
bool diverging_red = lfsr_tag_isred(p[0].alt)
&& lfsr_tag_diverging(
p[0].alt, p[0].weight,
lower_rid, upper_rid,
a_rid, a_tag,
b_rid, b_tag);
if (!diverged
// diverging black?
&& (lfsr_tag_isblack(alt)
// give up if we find a yellow alt
|| lfsr_tag_isred(p[0].alt))
&& (lfsr_tag_diverging2(
alt, weight,
p[0].alt, p[0].weight,
lower_rid, upper_rid,
a_rid, a_tag,
b_rid, b_tag)
|| (lfsr_tag_isred(p[0].alt)
&& lfsr_tag_diverging(
p[0].alt, p[0].weight,
lower_rid, upper_rid,
a_rid, a_tag,
b_rid, b_tag)))) {
&& (diverging || diverging_red)) {
diverged = true;
// both diverged? collapse
if (lfsr_tag_diverging2(
alt, weight,
p[0].alt, p[0].weight,
lower_rid, upper_rid,
a_rid, a_tag,
b_rid, b_tag)
&& (lfsr_tag_isred(p[0].alt)
&& lfsr_tag_diverging(
p[0].alt, p[0].weight,
lower_rid, upper_rid,
a_rid, a_tag,
b_rid, b_tag))) {
// both diverging? collapse
if (diverging && diverging_red) {
LFS_ASSERT(a_rid < b_rid || a_tag < b_tag);
LFS_ASSERT(lfsr_tag_isparallel(alt, p[0].alt));
@@ -2997,15 +2987,8 @@ trunk:;
continue;
}
// force diverged alts to be pruned
} else if (diverged
&& lfsr_tag_diverging2(
alt, weight,
p[0].alt, p[0].weight,
lower_rid, upper_rid,
a_rid, a_tag,
b_rid, b_tag)) {
// one diverged? trim so alt is pruned
// trim diverging alts so they can be pruned
} else if (diverged && diverging) {
lfsr_tag_trim(
alt, weight,
&lower_rid, &upper_rid,