JavaScriptCore-7601.1.46.3.tar.gz

[apple/javascriptcore.git] / dfg / DFGLoopPreHeaderCreationPhase.cpp

diff --git a/dfg/DFGLoopPreHeaderCreationPhase.cpp b/dfg/DFGLoopPreHeaderCreationPhase.cpp
index b11b2dbc5ade8d042720847a498ecaccbf1574d9..340ef2d187b80780b8a9e97144e4c2b1d2b5ac47 100644 (file)
--- a/dfg/DFGLoopPreHeaderCreationPhase.cpp
+++ b/dfg/DFGLoopPreHeaderCreationPhase.cpp
@@ -42,7 +42,7 @@ BasicBlock* createPreHeader(Graph& graph, BlockInsertionSet& insertionSet, Basic
     // Don't bother to preserve execution frequencies for now.
     BasicBlock* preHeader = insertionSet.insertBefore(block, PNaN);
     preHeader->appendNode(
-        graph, SpecNone, Jump, block->at(0)->origin, OpInfo(block));
+        graph, SpecNone, Jump, block->firstOrigin(), OpInfo(block));
     
     for (unsigned predecessorIndex = 0; predecessorIndex < block->predecessors.size(); predecessorIndex++) {
         BasicBlock* predecessor = block->predecessors[predecessorIndex];
@@ -88,11 +88,23 @@ public:
                     existingPreHeader = predecessor;
                     continue;
                 }
-                if (existingPreHeader == predecessor)
-                    continue;
+                // We won't have duplicate entries in the predecessors list.
+                DFG_ASSERT(m_graph, nullptr, existingPreHeader != predecessor);
                 needsNewPreHeader = true;
                 break;
             }
+            
+            // This phase should only be run on a DFG where unreachable blocks have been pruned.
+            // We also don't allow loops back to root. This means that every loop header has got
+            // to have a pre-header.
+            DFG_ASSERT(m_graph, nullptr, existingPreHeader);
+            
+            // We are looking at the predecessors of a loop header. A loop header has to have
+            // some predecessor other than the pre-header. We must have broken critical edges
+            // because that is the DFG SSA convention. Therefore, each predecessor of the loop
+            // header must have only one successor.
+            DFG_ASSERT(m_graph, nullptr, existingPreHeader->terminal()->op() == Jump);
+            
             if (!needsNewPreHeader)
                 continue;