Changeset 192529 in webkit for trunk/Source/JavaScriptCore/dfg/DFGLoopPreHeaderCreationPhase.cpp

Timestamp:

Nov 17, 2015, 1:41:43 PM (10 years ago)

Author:

[email protected]

Message:

It's best for the DFG to always have some guess of basic block frequency
​https://bugs.webkit.org/show_bug.cgi?id=151350

Reviewed by Geoffrey Garen.

It'll simplify things for B3 if we always have some estimate of block frequency, even if it's not
a great estimate. Using NaN as an estimate is probably worse than using any non-NaN number.

• dfg/DFGByteCodeParser.cpp:

(JSC::DFG::ByteCodeParser::inlineCall):
(JSC::DFG::ByteCodeParser::handleInlining):
(JSC::DFG::ByteCodeParser::parseCodeBlock):

• dfg/DFGCriticalEdgeBreakingPhase.cpp:

(JSC::DFG::CriticalEdgeBreakingPhase::breakCriticalEdge):

• dfg/DFGLoopPreHeaderCreationPhase.cpp:

(JSC::DFG::createPreHeader):

File:

• trunk/Source/JavaScriptCore/dfg/DFGLoopPreHeaderCreationPhase.cpp (modified) (1 diff)

trunk/Source/JavaScriptCore/dfg/DFGLoopPreHeaderCreationPhase.cpp

@@ -65 +65 @@
     //
     // https://bugs.webkit.org/show_bug.cgi?id=148587
-    
-    // Don't bother to preserve execution frequencies for now.
-    BasicBlock* preHeader = insertionSet.insertBefore(block, PNaN);
+
+    // Determine a good frequency for the pre-header. It's definitely not the frequency of the loop body.
+    // Instead, we use the max of the frequencies of the loop body's non-loop predecessors.
+    float frequency = 0;
+    for (BasicBlock* predecessor : block->predecessors) {
+        if (graph.m_dominators->dominates(block, predecessor))
+            continue;
+        frequency = std::max(frequency, predecessor->executionCount);
+    }
+    BasicBlock* preHeader = insertionSet.insertBefore(block, frequency);
 
     // FIXME: It would be great if we put some effort into enabling exitOK at this origin, if it