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DBtiles.c: DBFreePaintPlane() remove the TiFree() deferred assumption 

The comment indicates the expectation that TiFree() is deferred-by-one,
which would be true if freeMalloc() was used but since the custom mmap()
allocator technically this is not true.

The TiFree() allocator is single-threaded and separate from libc so the
assumption is still kind of true but for different reasons
(single-threaded).

But since it doesn't really cost anything (other than a few lines of
code a human needs to read) the compiler would be expected to perform a
load (which it was going to do anyway) into a caller-saves register over
the function call.
Most of the other function state is invalidated anyway due to the heavy
linked-list navigation and low number of local variables, I would not
think there is much register allocation pressure.

TODO this code can be tested by confirming zero allocations are active
and by invalidating (poison) all fields inside TiFree().
This commit is contained in:
Darryl L. Miles 2025-02-13 08:22:28 +00:00 committed by R. Timothy Edwards
parent 15e5b36f52
commit a6fd0ed320
1 changed files with 8 additions and 8 deletions
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16
database/DBtiles.c
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@ -723,9 +723,7 @@ enumerate:
*
* This procedure uses a carfully constructed non-recursive area
* enumeration algorithm. Care is taken to not access a tile that has
* been deallocated. The only exception is for a tile that has just been
* passed to free(), but no more calls to free() or malloc() have been made.
* Magic's malloc allows this.
* been deallocated.
*
* --------------------------------------------------------------------
*/
@ -740,6 +738,7 @@ DBFreePaintPlane(plane)
/* Start with the bottom-right non-infinity tile in the plane */
tp = BL(plane->pl_right);
Tile *delayed = NULL;
/* Each iteration visits another tile on the RHS of the search area */
while (BOTTOM(tp) < rect->r_ytop)
{
@ -762,9 +761,9 @@ enumerate:
/* Each iteration returns one tile further to the right */
while (RIGHT(tp) < rect->r_xtop)
{
TiFree(tp);
tpnew = RT(tp);
tp = TR(tp);
TiFree1(&delayed, tp);
tpnew = RT(tp); /* deref of delayed */
tp = TR(tp); /* deref of delayed */
if (CLIP_TOP(tpnew) <= CLIP_TOP(tp) && BOTTOM(tpnew) < rect->r_ytop)
{
tp = tpnew;
@ -772,13 +771,14 @@ enumerate:
}
}
TiFree(tp);
TiFree1(&delayed, tp);
/* At right edge -- walk up to next tile along the right edge */
tp = RT(tp);
tp = RT(tp); /* deref of delayed */
if (BOTTOM(tp) < rect->r_ytop) {
while(LEFT(tp) >= rect->r_xtop) tp = BL(tp);
}
}
TiFreeIf(delayed);
}
/*