nvc0/ir: avoid infinite recursion when finding first uses of tex

In certain circumstances, findFirstUses could end up doubling back on
instructions it had already processed, resulting in an infinite
recursion. Avoid this by keeping track of already-visited instructions.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=83079
Tested-by: Tobias Klausmann <tobias.johannes.klausmann@mni.thm.de>
Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
Cc: "10.2 10.3" <mesa-stable@lists.freedesktop.org>

1 files changed, 25 insertions, 7 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 7da9b0be7e8..92f9a156f7c 100644
--- a/src/gallium/drivers/nouveau/codegen/nv50_ir_lowering_nvc0.cpp
+++ b/src/gallium/drivers/nouveau/codegen/nv50_ir_lowering_nvc0.cpp
@@ -174,15 +174,31 @@ NVC0LegalizePostRA::findOverwritingDefs(const Instruction *texi,
 }
 
 void
-NVC0LegalizePostRA::findFirstUses(const Instruction *texi,
-                                  const Instruction *insn,
-                                  std::list<TexUse> &uses)
+NVC0LegalizePostRA::findFirstUses(
+      const Instruction *texi,
+      const Instruction *insn,
+      std::list<TexUse> &uses,
+      std::tr1::unordered_set<const Instruction *>& visited)
 {
    for (int d = 0; insn->defExists(d); ++d) {
       Value *v = insn->getDef(d);
       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.
+          */
+         if (visited.find(usei) != visited.end())
+            continue;
+
+         visited.insert(usei);
+
          if (usei->op == OP_PHI || usei->op == OP_UNION) {
             // need a barrier before WAW cases
             for (int s = 0; usei->srcExists(s); ++s) {
@@ -197,11 +213,11 @@ NVC0LegalizePostRA::findFirstUses(const Instruction *texi,
              usei->op == OP_PHI ||
              usei->op == OP_UNION) {
             // these uses don't manifest in the machine code
-            findFirstUses(texi, usei, uses);
+            findFirstUses(texi, usei, uses, visited);
          } else
          if (usei->op == OP_MOV && usei->getDef(0)->equals(usei->getSrc(0)) &&
              usei->subOp != NV50_IR_SUBOP_MOV_FINAL) {
-            findFirstUses(texi, usei, uses);
+            findFirstUses(texi, usei, uses, visited);
          } else {
             addTexUse(uses, usei, insn);
          }
@@ -257,8 +273,10 @@ NVC0LegalizePostRA::insertTextureBarriers(Function *fn)
    uses = new std::list<TexUse>[texes.size()];
    if (!uses)
       return false;
-   for (size_t i = 0; i < texes.size(); ++i)
-      findFirstUses(texes[i], texes[i], uses[i]);
+   for (size_t i = 0; i < texes.size(); ++i) {
+      std::tr1::unordered_set<const Instruction *> visited;
+      findFirstUses(texes[i], texes[i], uses[i], visited);
+   }
 
    // determine the barrier level at each use
    for (size_t i = 0; i < texes.size(); ++i) {