[llvm-commits] [llvm] r167942 - /llvm/trunk/lib/Transforms/Vectorize/BBVectorize.cpp

[Hal Finkel]

Author: hfinkel
Date: Wed Nov 14 12:38:11 2012
New Revision: 167942

URL: http://llvm.org/viewvc/llvm-project?rev=167942&view=rev
Log:
Fix the largest offender of determinism in BBVectorize

Iterating over the children of each node in the potential vectorization
plan must happen in a deterministic order (because it affects which children
are erased when two children conflict). There was no need for this data
structure to be a map in the first place, so replacing it with a vector
is a small change.

I believe that this was the last remaining instance if iterating over the
elements of a Dense* container where the iteration order could matter.
There are some remaining iterations over std::*map containers where the order
might matter, but so long as the Value* for instructions in a block increase
with the order of the instructions in the block (or decrease) monotonically,
then this will appear to be deterministic.

Modified:
    llvm/trunk/lib/Transforms/Vectorize/BBVectorize.cpp

Modified: llvm/trunk/lib/Transforms/Vectorize/BBVectorize.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Vectorize/BBVectorize.cpp?rev=167942&r1=167941&r2=167942&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Vectorize/BBVectorize.cpp (original)
+++ llvm/trunk/lib/Transforms/Vectorize/BBVectorize.cpp Wed Nov 14 12:38:11 2012
@@ -1485,7 +1485,7 @@
       PrunedTree.insert(QTop.first);
 
       // Visit each child, pruning as necessary...
-      DenseMap<ValuePair, size_t> BestChildren;
+      std::vector<ValuePairWithDepth> BestChildren;
       VPPIteratorPair QTopRange = ConnectedPairs.equal_range(QTop.first);
       for (std::multimap<ValuePair, ValuePair>::iterator K = QTopRange.first;
            K != QTopRange.second; ++K) {
@@ -1517,7 +1517,7 @@
         DenseSet<ValuePair> CurrentPairs;
 
         bool CanAdd = true;
-        for (DenseMap<ValuePair, size_t>::iterator C2
+        for (std::vector<ValuePairWithDepth>::iterator C2
               = BestChildren.begin(), E2 = BestChildren.end();
              C2 != E2; ++C2) {
           if (C2->first.first == C->first.first ||
@@ -1602,22 +1602,22 @@
         // to an already-selected child. Check for this here, and if a
         // conflict is found, then remove the previously-selected child
         // before adding this one in its place.
-        for (DenseMap<ValuePair, size_t>::iterator C2
+        for (std::vector<ValuePairWithDepth>::iterator C2
               = BestChildren.begin(); C2 != BestChildren.end();) {
           if (C2->first.first == C->first.first ||
               C2->first.first == C->first.second ||
               C2->first.second == C->first.first ||
               C2->first.second == C->first.second ||
               pairsConflict(C2->first, C->first, PairableInstUsers))
-            BestChildren.erase(C2++);
+            C2 = BestChildren.erase(C2);
           else
             ++C2;
         }
 
-        BestChildren.insert(ValuePairWithDepth(C->first, C->second));
+        BestChildren.push_back(ValuePairWithDepth(C->first, C->second));
       }
 
-      for (DenseMap<ValuePair, size_t>::iterator C
+      for (std::vector<ValuePairWithDepth>::iterator C
             = BestChildren.begin(), E2 = BestChildren.end();
            C != E2; ++C) {
         size_t DepthF = getDepthFactor(C->first.first);