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t: Changed lfsr_mtree_traverse to operate on mdir+mtraversal

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Separated out omdir/mdir and mtraversal. You still need to allocate an
mdir for mtraversal to work, but this avoids the extra cost of omdir's
linked-list.

To avoid _too_ many pointers, I duplicated the flags field into both
lfsr_traversal_t and lfsr_mtraversal_t. This is basically free since we
end up with a bunch of padding for mtraversal's state field, but comes
with the risk of getting confused when the two flag fields don't match
in the future.

I also merged the intermediary btype field into flags to avoid yet
another single-byte field, where it fits comfortably in 3-bits.

Note that the mdir can be uninitialized in cases where we don't need to
worry about traversal clobbering.

---

This has the same problems as separating out mdirs/bshrubs in bshrub
functions: more stack/code to move the multiple pointers around, but is
necessary to avoid strict aliasing issues. There's no way to represent
overlapping omdir/mdir/mtraversal struct in standard C99 otherwise.

The end result saves a bit of code, but adds a bit of stack:

           code          stack
  before: 34576           2632
  after:  34524 (-0.2%)   2640 (+0.3%)

Though these numbers may be close enough to the compiler noise floor to
not really care about...
This commit is contained in:
Christopher Haster
2024-06-23 23:21:34 -05:00
parent b383821a22
commit 2f1d711902
4 changed files with 151 additions and 149 deletions
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tests/test_alloc.toml
+6 -3
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@@ -163,6 +163,7 @@ code = '''
uint8_t *seen = malloc((BLOCK_COUNT+7)/8);
memset(seen, 0, (BLOCK_COUNT+7)/8);
lfsr_mdir_t mdir;
lfsr_mtraversal_t mt = LFSR_MTRAVERSAL(
(CKMETA) ? LFS_T_CKMETA : 0);
for (lfs_block_t i = 0;; i++) {
@@ -170,7 +171,7 @@ code = '''
assert(i < 2*BLOCK_COUNT);
lfsr_mtinfo_t mtinfo;
int err = lfsr_mtree_traverse(&lfs, &mt, &mtinfo);
int err = lfsr_mtree_traverse(&lfs, &mdir, &mt, &mtinfo);
assert(!err || err == LFS_ERR_NOENT);
if (err == LFS_ERR_NOENT) {
break;
@@ -331,6 +332,7 @@ code = '''
uint8_t *seen = malloc((BLOCK_COUNT+7)/8);
memset(seen, 0, (BLOCK_COUNT+7)/8);
lfsr_mdir_t mdir;
lfsr_mtraversal_t mt = LFSR_MTRAVERSAL(
((CKMETA) ? LFS_T_CKMETA : 0));
for (lfs_block_t i = 0;; i++) {
@@ -338,7 +340,7 @@ code = '''
assert(i < 2*BLOCK_COUNT);
lfsr_mtinfo_t mtinfo;
int err = lfsr_mtree_traverse(&lfs, &mt, &mtinfo);
int err = lfsr_mtree_traverse(&lfs, &mdir, &mt, &mtinfo);
assert(!err || err == LFS_ERR_NOENT);
if (err == LFS_ERR_NOENT) {
break;
@@ -485,6 +487,7 @@ code = '''
uint8_t *seen = malloc((BLOCK_COUNT+7)/8);
memset(seen, 0, (BLOCK_COUNT+7)/8);
lfsr_mdir_t mdir;
lfsr_mtraversal_t mt = LFSR_MTRAVERSAL(
((CKMETA) ? LFS_T_CKMETA : 0));
for (lfs_block_t i = 0;; i++) {
@@ -492,7 +495,7 @@ code = '''
assert(i < 2*BLOCK_COUNT);
lfsr_mtinfo_t mtinfo;
int err = lfsr_mtree_traverse(&lfs, &mt, &mtinfo);
int err = lfsr_mtree_traverse(&lfs, &mdir, &mt, &mtinfo);
assert(!err || err == LFS_ERR_NOENT);
if (err == LFS_ERR_NOENT) {
break;