commit 8c9dcace0d7fc13824fdb0aa8084ef33db7bf0cd
author Duncan P. N. Exon Smith <dexonsmith@apple.com> Fri Aug 07 00:44:55 2015 +0000
committer Duncan P. N. Exon Smith <dexonsmith@apple.com> Fri Aug 07 00:44:55 2015 +0000
tree 5a7129b284be9055439d288870ac5b5ebe886bf5
parent c9fdbdb78dd06ca1cf3d87f98c75ba7e4fe529e1

ValueMapper: Resolve uniquing cycles more aggressively

As a follow-up to r244181, resolve uniquing cycles underneath distinct
nodes on the fly.  This prevents uniquing cycles in early operands from
affecting later operands.  It also removes an iteration through distinct
nodes' operands.

No real functional change here, just more prompt resolution of temporary
nodes.

llvm-svn: 244302

llvm/lib/Transforms/Utils/ValueMapper.cpp

diff --git a/llvm/lib/Transforms/Utils/ValueMapper.cpp b/llvm/lib/Transforms/Utils/ValueMapper.cpp
index 85c751f..c9e474d 100644
--- a/llvm/lib/Transforms/Utils/ValueMapper.cpp
+++ b/llvm/lib/Transforms/Utils/ValueMapper.cpp
@@ -191,12 +191,18 @@
 }
 
 /// Remap the operands of an MDNode.
+///
+/// If \c Node is temporary, uniquing cycles are ignored.  If \c Node is
+/// distinct, uniquing cycles are resolved as they're found.
+///
+/// \pre \c Node.isDistinct() or \c Node.isTemporary().
 static bool remapOperands(MDNode &Node,
                           SmallVectorImpl<MDNode *> &DistinctWorklist,
                           ValueToValueMapTy &VM, RemapFlags Flags,
                           ValueMapTypeRemapper *TypeMapper,
                           ValueMaterializer *Materializer) {
   assert(!Node.isUniqued() && "Expected temporary or distinct node");
+  const bool IsDistinct = Node.isDistinct();
 
   bool AnyChanged = false;
   for (unsigned I = 0, E = Node.getNumOperands(); I != E; ++I) {
@@ -206,6 +212,11 @@
     if (Old != New) {
       AnyChanged = true;
       Node.replaceOperandWith(I, New);
+
+      // Resolve uniquing cycles underneath distinct nodes on the fly so they
+      // don't infect later operands.
+      if (IsDistinct)
+        resolveCycles(New);
     }
   }
 
@@ -332,15 +343,9 @@
   resolveCycles(NewMD);
 
   // Remap the operands of distinct MDNodes.
-  while (!DistinctWorklist.empty()) {
-    auto *N = DistinctWorklist.pop_back_val();
-
-    // If an operand changes, then it may be involved in a uniquing cycle.
-    if (remapOperands(*N, DistinctWorklist, VM, Flags, TypeMapper,
-                      Materializer))
-      for (Metadata *MD : N->operands())
-        resolveCycles(MD);
-  }
+  while (!DistinctWorklist.empty())
+    remapOperands(*DistinctWorklist.pop_back_val(), DistinctWorklist, VM, Flags,
+                  TypeMapper, Materializer);
 
   return NewMD;
 }