From 3f5bedf5cbde2cc2badc86b1a0b377f6efcde71c Mon Sep 17 00:00:00 2001
From: Jakob Stoklund Olesen <stoklund@2pi.dk>
Date: Mon, 11 Apr 2011 21:47:01 +0000
Subject: [PATCH] Speed up eviction by stopping collectInterferingVRegs as soon
 as the spill weight limit has been exceeded.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@129305 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/CodeGen/LiveIntervalUnion.cpp | 12 +++++++++---
 lib/CodeGen/LiveIntervalUnion.h   |  3 ++-
 lib/CodeGen/RegAllocGreedy.cpp    | 22 ++++++++++++----------
 3 files changed, 23 insertions(+), 14 deletions(-)

diff --git a/lib/CodeGen/LiveIntervalUnion.cpp b/lib/CodeGen/LiveIntervalUnion.cpp
index 51789998c65..b67f96667bf 100644
--- a/lib/CodeGen/LiveIntervalUnion.cpp
+++ b/lib/CodeGen/LiveIntervalUnion.cpp
@@ -176,6 +176,7 @@ LiveIntervalUnion::Query::firstInterference() {
     return FirstInterference;
   CheckedFirstInterference = true;
   InterferenceResult &IR = FirstInterference;
+  IR.LiveUnionI.setMap(LiveUnion->getMap());
 
   // Quickly skip interference check for empty sets.
   if (VirtReg->empty() || LiveUnion->empty()) {
@@ -184,10 +185,10 @@ LiveIntervalUnion::Query::firstInterference() {
     // VirtReg starts first, perform double binary search.
     IR.VirtRegI = VirtReg->find(LiveUnion->startIndex());
     if (IR.VirtRegI != VirtReg->end())
-      IR.LiveUnionI = LiveUnion->find(IR.VirtRegI->start);
+      IR.LiveUnionI.find(IR.VirtRegI->start);
   } else {
     // LiveUnion starts first, perform double binary search.
-    IR.LiveUnionI = LiveUnion->find(VirtReg->beginIndex());
+    IR.LiveUnionI.find(VirtReg->beginIndex());
     if (IR.LiveUnionI.valid())
       IR.VirtRegI = VirtReg->find(IR.LiveUnionI.start());
     else
@@ -243,7 +244,7 @@ bool LiveIntervalUnion::Query::isSeenInterference(LiveInterval *VirtReg) const {
 //
 // For comments on how to speed it up, see Query::findIntersection().
 unsigned LiveIntervalUnion::Query::
-collectInterferingVRegs(unsigned MaxInterferingRegs) {
+collectInterferingVRegs(unsigned MaxInterferingRegs, float MaxWeight) {
   InterferenceResult IR = firstInterference();
   LiveInterval::iterator VirtRegEnd = VirtReg->end();
   LiveInterval *RecentInterferingVReg = NULL;
@@ -285,6 +286,11 @@ collectInterferingVRegs(unsigned MaxInterferingRegs) {
       // Cache the most recent interfering vreg to bypass isSeenInterference.
       RecentInterferingVReg = IR.LiveUnionI.value();
       ++IR.LiveUnionI;
+
+      // Stop collecting when the max weight is exceeded.
+      if (RecentInterferingVReg->weight >= MaxWeight)
+        return InterferingVRegs.size();
+
       continue;
     }
     // VirtRegI may have advanced far beyond LiveUnionI,
diff --git a/lib/CodeGen/LiveIntervalUnion.h b/lib/CodeGen/LiveIntervalUnion.h
index 0964ecd07a8..90d4aaf88ad 100644
--- a/lib/CodeGen/LiveIntervalUnion.h
+++ b/lib/CodeGen/LiveIntervalUnion.h
@@ -226,7 +226,8 @@ public:
 
     // Count the virtual registers in this union that interfere with this
     // query's live virtual register, up to maxInterferingRegs.
-    unsigned collectInterferingVRegs(unsigned MaxInterferingRegs = UINT_MAX);
+    unsigned collectInterferingVRegs(unsigned MaxInterferingRegs = UINT_MAX,
+                                     float MaxWeight = HUGE_VALF);
 
     // Was this virtual register visited during collectInterferingVRegs?
     bool isSeenInterference(LiveInterval *VReg) const;
diff --git a/lib/CodeGen/RegAllocGreedy.cpp b/lib/CodeGen/RegAllocGreedy.cpp
index 7c2ed3fc4ee..f9e494f608e 100644
--- a/lib/CodeGen/RegAllocGreedy.cpp
+++ b/lib/CodeGen/RegAllocGreedy.cpp
@@ -336,22 +336,24 @@ LiveInterval *RAGreedy::dequeue() {
 //===----------------------------------------------------------------------===//
 
 /// canEvict - Return true if all interferences between VirtReg and PhysReg can
-/// be evicted. Set maxWeight to the maximal spill weight of an interference.
+/// be evicted.
+/// Return false if any interference is heavier than MaxWeight.
+/// On return, set MaxWeight to the maximal spill weight of an interference.
 bool RAGreedy::canEvictInterference(LiveInterval &VirtReg, unsigned PhysReg,
                                     float &MaxWeight) {
   float Weight = 0;
   for (const unsigned *AliasI = TRI->getOverlaps(PhysReg); *AliasI; ++AliasI) {
     LiveIntervalUnion::Query &Q = query(VirtReg, *AliasI);
-    // If there is 10 or more interferences, chances are one is smaller.
-    if (Q.collectInterferingVRegs(10) >= 10)
+    // If there is 10 or more interferences, chances are one is heavier.
+    if (Q.collectInterferingVRegs(10, MaxWeight) >= 10)
       return false;
 
-    // Check if any interfering live range is heavier than VirtReg.
-    for (unsigned i = 0, e = Q.interferingVRegs().size(); i != e; ++i) {
-      LiveInterval *Intf = Q.interferingVRegs()[i];
+    // Check if any interfering live range is heavier than MaxWeight.
+    for (unsigned i = Q.interferingVRegs().size(); i; --i) {
+      LiveInterval *Intf = Q.interferingVRegs()[i - 1];
       if (TargetRegisterInfo::isPhysicalRegister(Intf->reg))
         return false;
-      if (Intf->weight >= VirtReg.weight)
+      if (Intf->weight >= MaxWeight)
         return false;
       Weight = std::max(Weight, Intf->weight);
     }
@@ -370,17 +372,17 @@ unsigned RAGreedy::tryEvict(LiveInterval &VirtReg,
   NamedRegionTimer T("Evict", TimerGroupName, TimePassesIsEnabled);
 
   // Keep track of the lightest single interference seen so far.
-  float BestWeight = 0;
+  float BestWeight = VirtReg.weight;
   unsigned BestPhys = 0;
 
   Order.rewind();
   while (unsigned PhysReg = Order.next()) {
-    float Weight = 0;
+    float Weight = BestWeight;
     if (!canEvictInterference(VirtReg, PhysReg, Weight))
       continue;
 
     // This is an eviction candidate.
-    DEBUG(dbgs() << "max " << PrintReg(PhysReg, TRI) << " interference = "
+    DEBUG(dbgs() << PrintReg(PhysReg, TRI) << " interference = "
                  << Weight << '\n');
     if (BestPhys && Weight >= BestWeight)
       continue;