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[mono][interp] Link try bblock with leave targets from catch block #116298

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[mono][interp] Link try bblock with leave targets from catch block #116298

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52 changes: 52 additions & 0 deletions src/mono/mono/mini/interp/transform-opt.c
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Original file line number Diff line number Diff line change
Expand Up @@ -533,6 +533,55 @@ interp_get_bb_links (InterpBasicBlock *bb)
return str;
}

// This method links a try bblock (which can be part of the no-eh path, aka basic blocks that are reachable
// without an exception being thrown) with all exists from the catch bblock that go into no-eh bblocks.
// This is needed because for no-eh bblocks we do dominance computation. So if a no-eh bblock can be
// reached through an eh path, we need to have this information exposed.
static void
dfs_link_try_bblock (TransformData *td, InterpBasicBlock *catch_bb, InterpBasicBlock **stack, gboolean *marked)
{
int next_stack_index = 0;
stack [next_stack_index++] = catch_bb;
marked [catch_bb->dfs_index - td->bblocks_count_no_eh] = TRUE;

while (next_stack_index > 0) {
// Pop last added element
next_stack_index--;
InterpBasicBlock *bb = stack [next_stack_index];

// Push all nodes to process next
for (int i = 0; i < bb->out_count; i++) {
InterpBasicBlock *out_bb = bb->out_bb [i];
if (out_bb->dfs_index < td->bblocks_count_no_eh) {
interp_link_bblocks (td, catch_bb->try_bblock, out_bb);
if (td->verbose_level)
g_print ("\t linked try_bb BB%d to leave target BB%d\n", catch_bb->try_bblock->index, out_bb->index);
} else if (!marked [out_bb->dfs_index - td->bblocks_count_no_eh]) {
stack [next_stack_index++] = out_bb;
marked [out_bb->dfs_index - td->bblocks_count_no_eh] = TRUE;
}
}
}
}

static void
link_try_bblocks (TransformData *td)
{
if (td->header->num_clauses) {
int num_eh_bblocks = td->bblocks_count_eh - td->bblocks_count_no_eh;
InterpBasicBlock **stack = (InterpBasicBlock**)g_malloc0 (sizeof (InterpBasicBlock*) * num_eh_bblocks);
gboolean *marked = (gboolean*)g_malloc0 (sizeof (gboolean) * num_eh_bblocks);
for (int i = td->bblocks_count_no_eh; i < td->bblocks_count_eh; i++) {
if (td->bblocks [i]->try_bblock && td->bblocks [i]->try_bblock->dfs_index < td->bblocks_count_no_eh)
dfs_link_try_bblock (td, td->bblocks [i], stack, marked);
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I think the marked array should be reset between DFS runs.

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@BrzVlad BrzVlad Jun 5, 2025 •
edited
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This wasn't necessary because we would never scan overlapping regions of code. However, this made me realize that if we have the same pattern inside a catch handler, then once again this fix is not enough. Having those nested catch blocks scanned also seems to be getting a bit too complex for what it's worth. I think I'll just end up disabling SSA optimizations for methods where a leave in a catch goes to a bblock that is not already a successor for the try bblock.

}
g_free (stack);
g_free (marked);
}

td->linked_try_bblocks = TRUE;
}

static int
dfs_visit (TransformData *td)
{
Expand Down Expand Up @@ -592,6 +641,9 @@ interp_compute_dfs_indexes (TransformData *td)
}
td->bblocks_count_eh = dfs_index;

if (!td->linked_try_bblocks)
link_try_bblocks (td);

if (td->verbose_level) {
InterpBasicBlock *bb;
g_print ("\nBASIC BLOCK GRAPH:\n");
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1 change: 1 addition & 0 deletions src/mono/mono/mini/interp/transform.h
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Expand Up @@ -360,6 +360,7 @@ typedef struct
guint need_optimization_retry : 1;
guint disable_ssa : 1;
guint eh_vars_computed : 1;
guint linked_try_bblocks : 1;
guint retry_compilation : 1;
guint retry_with_inlining : 1;
} TransformData;
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