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ecksum: Adopted global constant in lfs3_gbmap_set_ when ecksum is NULL

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It's two words, and I've probably already spent too long fiddling around
with this.

This drops the messy NULL checks in lfs3_gbmap_set_, for a wrapper that
defaults to a global {.cksize=-1} ecksum when NULL.

---

Code changes, with both a compound literal (cl), and global
constant (gc). The current code uses a global constant:

                      code          stack          ctx
  before:            35144           2136          660
  after+cl:          35144 (+0.0%)   2136 (+0.0%)  660 (+0.0%)
  after+gc:          35144 (+0.0%)   2136 (+0.0%)  660 (+0.0%)

                      code          stack          ctx
  gbmap+np before:   38272           2144          776
  gbmap+np after+cl: 38412 (+0.4%)   2144 (+0.0%)  776 (+0.0%)
  gbmap+np after+gc: 38380 (+0.3%)   2144 (+0.0%)  776 (+0.0%)

                      code          stack          ctx
  gbmap+yp before:   38940           2168          796
  gbmap+yp after+cl: 38952 (+0.0%)   2168 (+0.0%)  796 (+0.0%)
  gbmap+yp after+gc: 38920 (-0.1%)   2168 (+0.0%)  796 (+0.0%)

It's interesting to note that while the global constant generally
reduces code cost, it prevents constant-expr optimizations from
eliminating the NULL checks when compiling without preerases (np).

Is that enough reason to revert this? Probably not. (1) The simpler
codebase, and reduced chance of forgetting a NULL check, is preferable,
and (2) we don't care about the code cost of niche gbmap configurations
as much as the non-gbmap modes.
This commit is contained in:
Christopher Haster
2025-12-29 23:49:19 -06:00
parent 8de1903172
commit 1d6fa2e5f1
1 changed files with 20 additions and 14 deletions
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lfs3.c
+20 -14
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@@ -10507,7 +10507,7 @@ static int lfs3_gbmap_commit(lfs3_t *lfs3, lfs3_btree_t *gbmap,
//
// the purpose of weight is really just to provide a shortcut for bulk
// clearing ranges in lfs3_alloc_lookgbmap
static int lfs3_gbmap_set_(lfs3_t *lfs3, lfs3_btree_t *gbmap,
static int lfs3_gbmap_set__(lfs3_t *lfs3, lfs3_btree_t *gbmap,
lfs3_block_t block, lfs3_block_t weight,
lfs3_tag_t tag, const lfs3_ecksum_t *ecksum) {
// lookup gbmap range
@@ -10522,10 +10522,7 @@ static int lfs3_gbmap_set_(lfs3_t *lfs3, lfs3_btree_t *gbmap,
}
// wait, already set to expected type? guess we're done
if (tag__ == tag
&& ((ecksum)
? lfs3_ecksum_cmp(&ecksum__, ecksum) == 0
: !lfs3_ecksum_isecksum(&ecksum__))) {
if (tag__ == tag && lfs3_ecksum_cmp(&ecksum__, ecksum) == 0) {
return 0;
}
@@ -10555,10 +10552,7 @@ static int lfs3_gbmap_set_(lfs3_t *lfs3, lfs3_btree_t *gbmap,
}
LFS3_ASSERT(r_weight == r_bid - block);
if (r_tag == tag
&& ((ecksum)
? lfs3_ecksum_cmp(&r_ecksum, ecksum) == 0
: !lfs3_ecksum_isecksum(&r_ecksum))) {
if (r_tag == tag && lfs3_ecksum_cmp(&r_ecksum, ecksum) == 0) {
// delete to prepare merge
int err = lfs3_gbmap_commit(lfs3, &gbmap_, r_bid, LFS3_RATTRS(
LFS3_RATTR(2, LFS3_tag_RM, -2),
@@ -10590,10 +10584,7 @@ static int lfs3_gbmap_set_(lfs3_t *lfs3, lfs3_btree_t *gbmap,
}
LFS3_ASSERT(l_bid == block-weight);
if (l_tag == tag
&& ((ecksum)
? lfs3_ecksum_cmp(&l_ecksum, ecksum) == 0
: !lfs3_ecksum_isecksum(&l_ecksum))) {
if (l_tag == tag && lfs3_ecksum_cmp(&l_ecksum, ecksum) == 0) {
// delete to prepare merge
int err = lfs3_gbmap_commit(lfs3, &gbmap_, l_bid, LFS3_RATTRS(
LFS3_RATTR(2, LFS3_tag_RM, -2),
@@ -10623,7 +10614,7 @@ static int lfs3_gbmap_set_(lfs3_t *lfs3, lfs3_btree_t *gbmap,
? LFS3_RATTR(2, LFS3_tag_GROW, -2)
: LFS3_RATTR(2, LFS3_tag_RM, -2),
LFS3_RATTR_WEIGHT(-((bid__+1) - (block-(weight-1)))),
(ecksum && lfs3_ecksum_isecksum(ecksum))
(lfs3_ecksum_isecksum(ecksum))
? LFS3_RATTR(3, tag, -2, LFS3_FROM_ECKSUM)
: LFS3_RATTR(3, tag, -2),
LFS3_RATTR_WEIGHT(+weight_),
@@ -10646,6 +10637,21 @@ static int lfs3_gbmap_set_(lfs3_t *lfs3, lfs3_btree_t *gbmap,
}
#endif
#if !defined(LFS3_RDONLY) && defined(LFS3_GBMAP)
static const lfs3_ecksum_t lfs3_gbmap_defaultecksum = {.cksize=-1};
#endif
#if !defined(LFS3_RDONLY) && defined(LFS3_GBMAP)
static int lfs3_gbmap_set_(lfs3_t *lfs3, lfs3_btree_t *gbmap,
lfs3_block_t block, lfs3_block_t weight,
lfs3_tag_t tag, const lfs3_ecksum_t *ecksum) {
return lfs3_gbmap_set__(lfs3, gbmap,
block, weight, tag,
// default to not-ecksum if NULL
(ecksum) ? ecksum : &lfs3_gbmap_defaultecksum);
}
#endif
#if !defined(LFS3_RDONLY) && defined(LFS3_GBMAP)
static int lfs3_gbmap_set(lfs3_t *lfs3, lfs3_btree_t *gbmap,
lfs3_block_t block, lfs3_tag_t tag, const lfs3_ecksum_t *ecksum) {