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Fix an edge case in the Tarjan GC bridge that leads to losing xref information #112825

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Merged
merged 3 commits into from
Mar 24, 2025
Merged

Fix an edge case in the Tarjan GC bridge that leads to losing xref information #112825

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058b135
Fix an edge case in the Tarjan SCC that lead to losing xref information
filipnavara Feb 23, 2025
e60945a
Add test case to sgen-bridge-pathologies and add an assert to catch t…
filipnavara Mar 3, 2025
dc9b877
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BrzVlad Mar 24, 2025
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15 changes: 13 additions & 2 deletions src/mono/mono/metadata/sgen-tarjan-bridge.c
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Original file line number Diff line number Diff line change
Expand Up @@ -736,19 +736,27 @@ create_scc (ScanData *data)
gboolean found = FALSE;
gboolean found_bridge = FALSE;
ColorData *color_data = NULL;
gboolean can_reduce_color = TRUE;

for (i = dyn_array_ptr_size (&loop_stack) - 1; i >= 0; --i) {
ScanData *other = (ScanData *)dyn_array_ptr_get (&loop_stack, i);
found_bridge |= other->is_bridge;
if (dyn_array_ptr_size (&other->xrefs) > 0) {
// This scc will have more xrefs than the ones from the color_merge_array,
// we will need to create a new color to store this information.
can_reduce_color = FALSE;
}
if (found_bridge || other == data)
break;
}

if (found_bridge) {
color_data = new_color (TRUE);
++num_colors_with_bridges;
} else {
} else if (can_reduce_color) {
color_data = reduce_color ();
} else {
color_data = new_color (FALSE);
}
#if DUMP_GRAPH
printf ("|SCC %p rooted in %s (%p) has bridge %d\n", color_data, safe_name_bridge (data->obj), data->obj, found_bridge);
Expand Down Expand Up @@ -785,8 +793,11 @@ create_scc (ScanData *data)

// Maybe we should make sure we are not adding duplicates here. It is not really a problem
// since we will get rid of duplicates before submitting the SCCs to the client in gather_xrefs
if (color_data)
if (color_data) {
add_other_colors (color_data, &other->xrefs);
} else {
g_assert (dyn_array_ptr_size (&other->xrefs) == 0);
}
dyn_array_ptr_uninit (&other->xrefs);

if (other == data) {
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2 changes: 1 addition & 1 deletion src/tests/GC/Features/Bridge/Bridge.cs
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Expand Up @@ -385,7 +385,7 @@ public static int Main(string[] args)

RunGraphTest(SetupDeadList);
RunGraphTest(SetupSelfLinks);
// RunGraphTest(NestedCycles); // Fixed by Filip
RunGraphTest(NestedCycles);
// RunGraphTest(Spider); // Crashes
return 100;
}
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