From 8ae37d343fd30f6d2d72dfd8b52f19e6b4170fb6 Mon Sep 17 00:00:00 2001
From: Hannes Verschore <hv1989@gmail.com>
Date: Thu, 21 Feb 2013 15:56:43 +0100
Subject: [PATCH] Bug 843518: IonMonkey: Run alias analysis when UCE removes
 dependency of an instruction, r=nmatsakis

---
 js/src/ion/UnreachableCodeElimination.cpp | 19 ++++++++++++++++---
 js/src/ion/UnreachableCodeElimination.h   |  6 ++++--
 2 files changed, 20 insertions(+), 5 deletions(-)

diff --git a/js/src/ion/UnreachableCodeElimination.cpp b/js/src/ion/UnreachableCodeElimination.cpp
index 6738a6364e4..75367fd313c 100644
--- a/js/src/ion/UnreachableCodeElimination.cpp
+++ b/js/src/ion/UnreachableCodeElimination.cpp
@@ -7,6 +7,7 @@
 
 #include "UnreachableCodeElimination.h"
 #include "IonAnalysis.h"
+#include "AliasAnalysis.h"
 
 using namespace js;
 using namespace ion;
@@ -70,6 +71,13 @@ UnreachableCodeElimination::removeUnmarkedBlocksAndCleanup()
     if (redundantPhis_ && !EliminatePhis(mir_, graph_, ConservativeObservability))
         return false;
 
+    // Pass 4: Rerun alias analysis
+    if (rerunAliasAnalysis_) {
+        AliasAnalysis analysis(mir_, graph_);
+        if (!analysis.analyze())
+            return false;
+    }
+
     return true;
 }
 
@@ -128,8 +136,13 @@ UnreachableCodeElimination::prunePointlessBranchesAndMarkReachableBlocks()
 }
 
 void
-UnreachableCodeElimination::removeUsesFromUnmarkedBlocks(MDefinition *instr)
+UnreachableCodeElimination::checkDependencyAndRemoveUsesFromUnmarkedBlocks(MDefinition *instr)
 {
+    // When the instruction depends on removed block,
+    // alias analysis needs to get rerun to have the right dependency.
+    if (instr->dependency() && !instr->dependency()->block()->isMarked())
+        rerunAliasAnalysis_ = true;
+
     for (MUseIterator iter(instr->usesBegin()); iter != instr->usesEnd(); ) {
         if (!iter->consumer()->block()->isMarked())
             iter = instr->removeUse(iter);
@@ -161,9 +174,9 @@ UnreachableCodeElimination::removeUnmarkedBlocksAndClearDominators()
         if (block->isMarked()) {
             block->setId(--id);
             for (MPhiIterator iter(block->phisBegin()); iter != block->phisEnd(); iter++)
-                removeUsesFromUnmarkedBlocks(*iter);
+                checkDependencyAndRemoveUsesFromUnmarkedBlocks(*iter);
             for (MInstructionIterator iter(block->begin()); iter != block->end(); iter++)
-                removeUsesFromUnmarkedBlocks(*iter);
+                checkDependencyAndRemoveUsesFromUnmarkedBlocks(*iter);
         } else {
             if (block->numPredecessors() > 1) {
                 // If this block had phis, then any reachable
diff --git a/js/src/ion/UnreachableCodeElimination.h b/js/src/ion/UnreachableCodeElimination.h
index 4e7e7e007a6..99a61eed7b7 100644
--- a/js/src/ion/UnreachableCodeElimination.h
+++ b/js/src/ion/UnreachableCodeElimination.h
@@ -22,9 +22,10 @@ class UnreachableCodeElimination
     MIRGraph &graph_;
     uint32_t marked_;
     bool redundantPhis_;
+    bool rerunAliasAnalysis_;
 
     bool prunePointlessBranchesAndMarkReachableBlocks();
-    void removeUsesFromUnmarkedBlocks(MDefinition *instr);
+    void checkDependencyAndRemoveUsesFromUnmarkedBlocks(MDefinition *instr);
     bool removeUnmarkedBlocksAndClearDominators();
     bool removeUnmarkedBlocksAndCleanup();
 
@@ -33,7 +34,8 @@ class UnreachableCodeElimination
       : mir_(mir),
         graph_(graph),
         marked_(0),
-        redundantPhis_(false)
+        redundantPhis_(false),
+        rerunAliasAnalysis_(false)
     {}
 
     // Walks the graph and discovers what is reachable. Removes everything else.