From 4f6364fd3f2af74330b1bc4e545173af074707a5 Mon Sep 17 00:00:00 2001
From: Jakob Stoklund Olesen <stoklund@2pi.dk>
Date: Wed, 9 Feb 2011 21:52:03 +0000
Subject: [PATCH] Add tags to live interval unions to avoid using stale
 queries.

The tag is updated whenever the live interval union is changed, and it is tested
before using cached information.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@125224 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/CodeGen/LiveIntervalUnion.cpp |  2 ++
 lib/CodeGen/LiveIntervalUnion.h   | 15 +++++++++++++--
 2 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/lib/CodeGen/LiveIntervalUnion.cpp b/lib/CodeGen/LiveIntervalUnion.cpp
index 2027db19b75..205f28a0d65 100644
--- a/lib/CodeGen/LiveIntervalUnion.cpp
+++ b/lib/CodeGen/LiveIntervalUnion.cpp
@@ -28,6 +28,7 @@ using namespace llvm;
 void LiveIntervalUnion::unify(LiveInterval &VirtReg) {
   if (VirtReg.empty())
     return;
+  ++Tag;
 
   // Insert each of the virtual register's live segments into the map.
   LiveInterval::iterator RegPos = VirtReg.begin();
@@ -46,6 +47,7 @@ void LiveIntervalUnion::unify(LiveInterval &VirtReg) {
 void LiveIntervalUnion::extract(LiveInterval &VirtReg) {
   if (VirtReg.empty())
     return;
+  ++Tag;
 
   // Remove each of the virtual register's live segments from the map.
   LiveInterval::iterator RegPos = VirtReg.begin();
diff --git a/lib/CodeGen/LiveIntervalUnion.h b/lib/CodeGen/LiveIntervalUnion.h
index ff23cf61a33..6f9c5f4455e 100644
--- a/lib/CodeGen/LiveIntervalUnion.h
+++ b/lib/CodeGen/LiveIntervalUnion.h
@@ -64,10 +64,12 @@ public:
 
 private:
   const unsigned RepReg;  // representative register number
+  unsigned Tag;           // unique tag for current contents.
   LiveSegments Segments;  // union of virtual reg segments
 
 public:
-  LiveIntervalUnion(unsigned r, Allocator &a) : RepReg(r), Segments(a) {}
+  LiveIntervalUnion(unsigned r, Allocator &a) : RepReg(r), Tag(0), Segments(a)
+    {}
 
   // Iterate over all segments in the union of live virtual registers ordered
   // by their starting position.
@@ -81,6 +83,12 @@ public:
   typedef LiveSegments Map;
   const Map &getMap() { return Segments; }
 
+  /// getTag - Return an opaque tag representing the current state of the union.
+  unsigned getTag() const { return Tag; }
+
+  /// changedSince - Return true if the union change since getTag returned tag.
+  bool changedSince(unsigned tag) const { return tag != Tag; }
+
   // Add a live virtual register to this union and merge its segments.
   void unify(LiveInterval &VirtReg);
 
@@ -155,6 +163,7 @@ public:
     bool CheckedFirstInterference;
     bool SeenAllInterferences;
     bool SeenUnspillableVReg;
+    unsigned Tag;
 
   public:
     Query(): LiveUnion(), VirtReg() {}
@@ -171,17 +180,19 @@ public:
       CheckedFirstInterference = false;
       SeenAllInterferences = false;
       SeenUnspillableVReg = false;
+      Tag = 0;
     }
 
     void init(LiveInterval *VReg, LiveIntervalUnion *LIU) {
       assert(VReg && LIU && "Invalid arguments");
-      if (VirtReg == VReg && LiveUnion == LIU) {
+      if (VirtReg == VReg && LiveUnion == LIU && !LIU->changedSince(Tag)) {
         // Retain cached results, e.g. firstInterference.
         return;
       }
       clear();
       LiveUnion = LIU;
       VirtReg = VReg;
+      Tag = LIU->getTag();
     }
 
     LiveInterval &virtReg() const {