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rbyd-rr: Rearranged some things so appendattr gotos make a bit more sense

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- Renamed again: -> trunk:
- Added stem:, moved the awkward pre-stem logic into the not-alt check
- Kept leaf: unchanged

This organizes lfsr_rbyd_appendattr into logical trunk -> stem -> leaf
stages, which I think makes quite a bit of sense.

GCC is happy if we change the loop termination into goto stem, but I
think it's quite unfortunate that GCC's -Wunused-label warning
discourages labels for purely code organization. They're quite useful
for organizing complicated functions at a level higher than comments,
and GDB's break func:label syntax shows potential for external tooling.

Maybe we should disable -Wunused-label?

---

Not sure why this impacted code size, the transformation should have
been a noop. Then again, it's not too surprising, gotos are supposedly
pretty annoying to optimize around:

           code          stack
  before: 34480           2864
  after:  34468 (-0.5%)   2864 (+0.0%)

                     code          frame          stack
  appendattr before: 2404            216            568
  appendattr after:  2390 (-0.6%)    216 (+0.0%)    568 (+0.0%)
This commit is contained in:
Christopher Haster
2024-04-08 09:40:31 -05:00
parent 54c8beee70
commit 01b28b3224
1 changed files with 45 additions and 44 deletions
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lfs.c
+45 -44
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@@ -2852,9 +2852,6 @@ static int lfsr_rbyd_appendattr(lfs_t *lfs, lfsr_rbyd_t *rbyd,
a_tag = lfs_max16(a_tag, 0x1);
b_tag = lfs_max16(b_tag, 0x1);
// follow the current trunk
lfs_size_t branch = lfsr_rbyd_trunk(rbyd);
// keep track of diverged state
//
// this is only used if we operate on a range of tags, in which case
@@ -2869,7 +2866,10 @@ static int lfsr_rbyd_appendattr(lfs_t *lfs, lfsr_rbyd_t *rbyd,
lfsr_srid_t d_rid = 0;
lfsr_tag_t d_tag = 0;
again:;
// follow the current trunk
lfs_size_t branch = lfsr_rbyd_trunk(rbyd);
trunk:;
// the new trunk starts here
lfs_size_t trunk_ = rbyd->eoff;
@@ -3227,49 +3227,50 @@ again:;
} else {
// update the found tag
tag_ = lfsr_tag_key(alt);
break;
// the last alt should always end up black
LFS_ASSERT(lfsr_tag_isblack(p[0].alt));
// diverged lower trunk? move on to upper trunk
if (d_state == LFSR_D_DIVERGEDLOWER) {
d_state = LFSR_D_NOTDIVERGEDUPPER;
// keep track of the lower diverged bound
d_rid = lower_rid;
d_tag = lower_tag;
// flush any pending alts
err = lfsr_rbyd_p_flush(lfs, rbyd, p, 3);
if (err) {
return err;
}
// terminate diverged trunk with an unreachable tag
err = lfsr_rbyd_appendattr_(lfs, rbyd,
(lfsr_rbyd_isshrub(rbyd) ? LFSR_TAG_SHRUB : 0)
| LFSR_TAG_NULL,
0,
LFSR_DATA_NULL());
if (err) {
return err;
}
// swap tag/rid and move on to upper trunk
branch = trunk_;
lfs_swap16(&a_tag, &b_tag);
lfs_sswap32(&a_rid, &b_rid);
goto trunk;
} else if (d_state == LFSR_D_DIVERGEDUPPER) {
// use the lower diverged bound for leaf weight calculation
lower_rid = d_rid;
lower_tag = d_tag;
}
goto stem;
}
}
// the last alt should always end up black
LFS_ASSERT(lfsr_tag_isblack(p[0].alt));
// diverged lower trunk? move on to upper trunk
if (d_state == LFSR_D_DIVERGEDLOWER) {
d_state = LFSR_D_NOTDIVERGEDUPPER;
// keep track of the lower diverged bound
d_rid = lower_rid;
d_tag = lower_tag;
// flush any pending alts
err = lfsr_rbyd_p_flush(lfs, rbyd, p, 3);
if (err) {
return err;
}
// terminate diverged trunk with an unreachable tag
err = lfsr_rbyd_appendattr_(lfs, rbyd,
(lfsr_rbyd_isshrub(rbyd) ? LFSR_TAG_SHRUB : 0)
| LFSR_TAG_NULL,
0,
LFSR_DATA_NULL());
if (err) {
return err;
}
// swap tag/rid and move on to upper trunk
// TODO handle trunk differently? do we need to bother to stage this?
branch = trunk_;
lfs_swap16(&a_tag, &b_tag);
lfs_sswap32(&a_rid, &b_rid);
goto again;
} else if (d_state == LFSR_D_DIVERGEDUPPER) {
// use the lower diverged bound for leaf weight calculation
lower_rid = d_rid;
lower_tag = d_tag;
}
stem:;
// split leaf nodes?
//
// note we bias the weights here so that lfsr_rbyd_lookupnext