From: Jakob Stoklund Olesen <stoklund@2pi.dk>
Date: Fri, 3 Aug 2012 20:10:24 +0000 (+0000)
Subject: Make the hasPHIKills flag a computed property.
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=0ab7103e06ee1da7bde5b196a68be77ab49a005d;p=oota-llvm.git

Make the hasPHIKills flag a computed property.

The VNInfo::HAS_PHI_KILL is only half supported. We precompute it in
LiveIntervalAnalysis, but it isn't properly updated by live range
splitting and functions like shrinkToUses().

It is only used in one place: RegisterCoalescer::removeCopyByCommutingDef().

This patch changes that function to use a new LiveIntervals::hasPHIKill()
function that computes the flag for a given value number.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@161254 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/include/llvm/CodeGen/LiveIntervalAnalysis.h b/include/llvm/CodeGen/LiveIntervalAnalysis.h
index abeb0fbf817..da521dbc535 100644
--- a/include/llvm/CodeGen/LiveIntervalAnalysis.h
+++ b/include/llvm/CodeGen/LiveIntervalAnalysis.h
@@ -246,6 +246,10 @@ namespace llvm {
     /// return NULL.
     MachineBasicBlock *intervalIsInOneMBB(const LiveInterval &LI) const;
 
+    /// Returns true if VNI is killed by any PHI-def values in LI.
+    /// This may conservatively return true to avoid expensive computations.
+    bool hasPHIKill(const LiveInterval &LI, const VNInfo *VNI) const;
+
     /// addKillFlags - Add kill flags to any instruction that kills a virtual
     /// register.
     void addKillFlags();
diff --git a/lib/CodeGen/LiveIntervalAnalysis.cpp b/lib/CodeGen/LiveIntervalAnalysis.cpp
index 31f938e4354..54d665595c0 100644
--- a/lib/CodeGen/LiveIntervalAnalysis.cpp
+++ b/lib/CodeGen/LiveIntervalAnalysis.cpp
@@ -780,6 +780,25 @@ LiveIntervals::intervalIsInOneMBB(const LiveInterval &LI) const {
   return MBB1 == MBB2 ? MBB1 : NULL;
 }
 
+bool
+LiveIntervals::hasPHIKill(const LiveInterval &LI, const VNInfo *VNI) const {
+  for (LiveInterval::const_vni_iterator I = LI.vni_begin(), E = LI.vni_end();
+       I != E; ++I) {
+    const VNInfo *PHI = *I;
+    if (PHI->isUnused() || !PHI->isPHIDef())
+      continue;
+    const MachineBasicBlock *PHIMBB = getMBBFromIndex(PHI->def);
+    // Conservatively return true instead of scanning huge predecessor lists.
+    if (PHIMBB->pred_size() > 100)
+      return true;
+    for (MachineBasicBlock::const_pred_iterator
+         PI = PHIMBB->pred_begin(), PE = PHIMBB->pred_end(); PI != PE; ++PI)
+      if (VNI == LI.getVNInfoBefore(Indexes->getMBBEndIdx(*PI)))
+        return true;
+  }
+  return false;
+}
+
 float
 LiveIntervals::getSpillWeight(bool isDef, bool isUse, unsigned loopDepth) {
   // Limit the loop depth ridiculousness.
diff --git a/lib/CodeGen/RegisterCoalescer.cpp b/lib/CodeGen/RegisterCoalescer.cpp
index 349fcde5ef7..ebac8f14bc1 100644
--- a/lib/CodeGen/RegisterCoalescer.cpp
+++ b/lib/CodeGen/RegisterCoalescer.cpp
@@ -494,6 +494,11 @@ bool RegisterCoalescer::hasOtherReachingDefs(LiveInterval &IntA,
                                              LiveInterval &IntB,
                                              VNInfo *AValNo,
                                              VNInfo *BValNo) {
+  // If AValNo has PHI kills, conservatively assume that IntB defs can reach
+  // the PHI values.
+  if (LIS->hasPHIKill(IntA, AValNo))
+    return true;
+
   for (LiveInterval::iterator AI = IntA.begin(), AE = IntA.end();
        AI != AE; ++AI) {
     if (AI->valno != AValNo) continue;
@@ -558,10 +563,7 @@ bool RegisterCoalescer::removeCopyByCommutingDef(const CoalescerPair &CP,
   // AValNo is the value number in A that defines the copy, A3 in the example.
   VNInfo *AValNo = IntA.getVNInfoAt(CopyIdx.getRegSlot(true));
   assert(AValNo && "COPY source not live");
-
-  // If other defs can reach uses of this def, then it's not safe to perform
-  // the optimization.
-  if (AValNo->isPHIDef() || AValNo->isUnused() || AValNo->hasPHIKill())
+  if (AValNo->isPHIDef() || AValNo->isUnused())
     return false;
   MachineInstr *DefMI = LIS->getInstructionFromIndex(AValNo->def);
   if (!DefMI)