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-rw-r--r--src/gallium/drivers/nouveau/codegen/nv50_ir_lowering_nvc0.cpp16
1 files changed, 7 insertions, 9 deletions
diff --git a/src/gallium/drivers/nouveau/codegen/nv50_ir_lowering_nvc0.cpp b/src/gallium/drivers/nouveau/codegen/nv50_ir_lowering_nvc0.cpp
index ea1a17a445d..793393dd1cd 100644
--- a/src/gallium/drivers/nouveau/codegen/nv50_ir_lowering_nvc0.cpp
+++ b/src/gallium/drivers/nouveau/codegen/nv50_ir_lowering_nvc0.cpp
@@ -243,15 +243,13 @@ NVC0LegalizePostRA::findFirstUses(
for (Value::UseIterator u = v->uses.begin(); u != v->uses.end(); ++u) {
Instruction *usei = (*u)->getInsn();
- /* XXX HACK ALERT XXX
- *
- * This shouldn't have to be here, we should always be making forward
- * progress by looking at the uses. However this somehow does not
- * appear to be the case. Probably because this is being done right
- * after RA, when the defs/uses lists have been messed with by node
- * merging. This should probably be moved to being done right before
- * RA. But this will do for now.
- */
+ // NOTE: In case of a loop that overwrites a value but never uses
+ // it, it can happen that we have a cycle of uses that consists only
+ // of phis and no-op moves and will thus cause an infinite loop here
+ // since these are not considered actual uses.
+ // The most obvious (and perhaps the only) way to prevent this is to
+ // remember which instructions we've already visited.
+
if (visited.find(usei) != visited.end())
continue;