From c7d6078a3a7b2836f045c32cd9129e9bb0776ac3 Mon Sep 17 00:00:00 2001
From: Dan Gohman <sunfish@mozilla.com>
Date: Tue, 20 May 2014 13:36:40 -0700
Subject: [PATCH] Bug 1012964 - IonMonkey: Optimize LiveInterval::addRange.
 r=bhackett

---
 js/src/jit/LiveRangeAllocator.cpp | 30 ++++++++++++++++++------------
 mfbt/Vector.h                     | 22 ++++++++++++++++++++--
 2 files changed, 38 insertions(+), 14 deletions(-)

diff --git a/js/src/jit/LiveRangeAllocator.cpp b/js/src/jit/LiveRangeAllocator.cpp
index d8ce72de694..5cac4eef048 100644
--- a/js/src/jit/LiveRangeAllocator.cpp
+++ b/js/src/jit/LiveRangeAllocator.cpp
@@ -76,6 +76,7 @@ bool
 LiveInterval::addRangeAtHead(CodePosition from, CodePosition to)
 {
     JS_ASSERT(from < to);
+    JS_ASSERT(ranges_.empty() || from <= ranges_.back().from);
 
     Range newRange(from, to);
 
@@ -110,23 +111,28 @@ LiveInterval::addRange(CodePosition from, CodePosition to)
 
     Range *i;
     // Find the location to insert the new range
-    for (i = ranges_.end() - 1; i >= ranges_.begin(); i--) {
-        if (newRange.from <= i->to) {
-            if (i->from < newRange.from)
-                newRange.from = i->from;
+    for (i = ranges_.end(); i > ranges_.begin(); i--) {
+        if (newRange.from <= i[-1].to) {
+            if (i[-1].from < newRange.from)
+                newRange.from = i[-1].from;
             break;
         }
     }
     // Perform coalescing on overlapping ranges
-    for (; i >= ranges_.begin(); i--) {
-        if (newRange.to < i->from)
+    Range *j = i;
+    for (; i > ranges_.begin(); i--) {
+        if (newRange.to < i[-1].from)
             break;
-        if (newRange.to < i->to)
-            newRange.to = i->to;
-        ranges_.erase(i);
+        if (newRange.to < i[-1].to)
+            newRange.to = i[-1].to;
     }
 
-    return ranges_.insert(i + 1, newRange);
+    if (i == j)
+        return ranges_.insert(i, newRange);
+
+    i[0] = newRange;
+    ranges_.erase(i + 1, j);
+    return true;
 }
 
 void
@@ -134,10 +140,10 @@ LiveInterval::setFrom(CodePosition from)
 {
     while (!ranges_.empty()) {
         if (ranges_.back().to < from) {
-            ranges_.erase(&ranges_.back());
+            ranges_.popBack();
         } else {
             if (from == ranges_.back().to)
-                ranges_.erase(&ranges_.back());
+                ranges_.popBack();
             else
                 ranges_.back().from = from;
             break;
diff --git a/mfbt/Vector.h b/mfbt/Vector.h
index 4d283dfd5b6..9f4f898d74c 100644
--- a/mfbt/Vector.h
+++ b/mfbt/Vector.h
@@ -543,6 +543,12 @@ class VectorBase : private AllocPolicy
      */
     void erase(T* t);
 
+    /**
+     * Removes the elements [|b|, |e|), which must fall in the bounds [begin, end),
+     * shifting existing elements from |e + 1| onward to b's old position.
+     */
+    void erase(T* b, T *e);
+
     /**
      * Measure the size of the vector's heap-allocated storage.
      */
@@ -974,10 +980,22 @@ VectorBase<T, N, AP, TV>::erase(T* it)
   MOZ_ASSERT(begin() <= it);
   MOZ_ASSERT(it < end());
   while (it + 1 < end()) {
-    *it = *(it + 1);
+    *it = Move(*(it + 1));
     ++it;
   }
-    popBack();
+  popBack();
+}
+
+template<typename T, size_t N, class AP, class TV>
+inline void
+VectorBase<T, N, AP, TV>::erase(T* b, T *e)
+{
+  MOZ_ASSERT(begin() <= b);
+  MOZ_ASSERT(b <= e);
+  MOZ_ASSERT(e <= end());
+  while (e < end())
+    *b++ = Move(*e++);
+  shrinkBy(e - b);
 }
 
 template<typename T, size_t N, class AP, class TV>