Moved spill weight calculation out of SimpleRegisterCoalescing and into its own pass: CalculateSpillWeights.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@91273 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 154 insertions, 0 deletions

diff --git a/lib/CodeGen/CalcSpillWeights.cpp b/lib/CodeGen/CalcSpillWeights.cpp
new file mode 100644
index 0000000000..dcffb8a247
--- /dev/null
+++ b/lib/CodeGen/CalcSpillWeights.cpp
@@ -0,0 +1,154 @@
+//===------------------------ CalcSpillWeights.cpp ------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#define DEBUG_TYPE "calcspillweights"
+
+#include "llvm/Function.h"
+#include "llvm/ADT/SmallSet.h"
+#include "llvm/CodeGen/CalcSpillWeights.h"
+#include "llvm/CodeGen/LiveIntervalAnalysis.h"
+#include "llvm/CodeGen/MachineFunction.h"
+#include "llvm/CodeGen/MachineLoopInfo.h"
+#include "llvm/CodeGen/MachineRegisterInfo.h"
+#include "llvm/CodeGen/SlotIndexes.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/raw_ostream.h"
+#include "llvm/Target/TargetInstrInfo.h"
+#include "llvm/Target/TargetRegisterInfo.h"
+
+using namespace llvm;
+
+char CalculateSpillWeights::ID = 0;
+static RegisterPass<CalculateSpillWeights> X("calcspillweights",
+                                             "Calculate spill weights");
+
+void CalculateSpillWeights::getAnalysisUsage(AnalysisUsage &au) const {
+  au.addRequired<LiveIntervals>();
+  au.addRequired<MachineLoopInfo>();
+  au.setPreservesAll();
+  MachineFunctionPass::getAnalysisUsage(au);
+}
+
+bool CalculateSpillWeights::runOnMachineFunction(MachineFunction &fn) {
+
+  DEBUG(errs() << "********** Compute Spill Weights **********\n"
+               << "********** Function: "
+               << fn.getFunction()->getName() << '\n');
+
+  LiveIntervals *lis = &getAnalysis<LiveIntervals>();
+  MachineLoopInfo *loopInfo = &getAnalysis<MachineLoopInfo>();
+  const TargetInstrInfo *tii = fn.getTarget().getInstrInfo();
+  MachineRegisterInfo *mri = &fn.getRegInfo();
+
+  SmallSet<unsigned, 4> processed;
+  for (MachineFunction::iterator mbbi = fn.begin(), mbbe = fn.end();
+       mbbi != mbbe; ++mbbi) {
+    MachineBasicBlock* mbb = mbbi;
+    SlotIndex mbbEnd = lis->getMBBEndIdx(mbb);
+    MachineLoop* loop = loopInfo->getLoopFor(mbb);
+    unsigned loopDepth = loop ? loop->getLoopDepth() : 0;
+    bool isExiting = loop ? loop->isLoopExiting(mbb) : false;
+
+    for (MachineBasicBlock::const_iterator mii = mbb->begin(), mie = mbb->end();
+         mii != mie; ++mii) {
+      const MachineInstr *mi = mii;
+      if (tii->isIdentityCopy(*mi))
+        continue;
+
+      if (mi->getOpcode() == TargetInstrInfo::IMPLICIT_DEF)
+        continue;
+
+      for (unsigned i = 0, e = mi->getNumOperands(); i != e; ++i) {
+        const MachineOperand &mopi = mi->getOperand(i);
+        if (!mopi.isReg() || mopi.getReg() == 0)
+          continue;
+        unsigned reg = mopi.getReg();
+        if (!TargetRegisterInfo::isVirtualRegister(mopi.getReg()))
+          continue;
+        // Multiple uses of reg by the same instruction. It should not
+        // contribute to spill weight again.
+        if (!processed.insert(reg))
+          continue;
+
+        bool hasDef = mopi.isDef();
+        bool hasUse = !hasDef;
+        for (unsigned j = i+1; j != e; ++j) {
+          const MachineOperand &mopj = mi->getOperand(j);
+          if (!mopj.isReg() || mopj.getReg() != reg)
+            continue;
+          hasDef |= mopj.isDef();
+          hasUse |= mopj.isUse();
+          if (hasDef && hasUse)
+            break;
+        }
+
+        LiveInterval &regInt = lis->getInterval(reg);
+        float weight = lis->getSpillWeight(hasDef, hasUse, loopDepth);
+        if (hasDef && isExiting) {
+          // Looks like this is a loop count variable update.
+          SlotIndex defIdx = lis->getInstructionIndex(mi).getDefIndex();
+          const LiveRange *dlr =
+            lis->getInterval(reg).getLiveRangeContaining(defIdx);
+          if (dlr->end > mbbEnd)
+            weight *= 3.0F;
+        }
+        regInt.weight += weight;
+      }
+      processed.clear();
+    }
+  }
+
+  for (LiveIntervals::iterator I = lis->begin(), E = lis->end(); I != E; ++I) {
+    LiveInterval &li = *I->second;
+    if (TargetRegisterInfo::isVirtualRegister(li.reg)) {
+      // If the live interval length is essentially zero, i.e. in every live
+      // range the use follows def immediately, it doesn't make sense to spill
+      // it and hope it will be easier to allocate for this li.
+      if (isZeroLengthInterval(&li)) {
+        li.weight = HUGE_VALF;
+        continue;
+      }
+
+      bool isLoad = false;
+      SmallVector<LiveInterval*, 4> spillIs;
+      if (lis->isReMaterializable(li, spillIs, isLoad)) {
+        // If all of the definitions of the interval are re-materializable,
+        // it is a preferred candidate for spilling. If non of the defs are
+        // loads, then it's potentially very cheap to re-materialize.
+        // FIXME: this gets much more complicated once we support non-trivial
+        // re-materialization.
+        if (isLoad)
+          li.weight *= 0.9F;
+        else
+          li.weight *= 0.5F;
+      }
+
+      // Slightly prefer live interval that has been assigned a preferred reg.
+      std::pair<unsigned, unsigned> Hint = mri->getRegAllocationHint(li.reg);
+      if (Hint.first || Hint.second)
+        li.weight *= 1.01F;
+
+      // Divide the weight of the interval by its size.  This encourages
+      // spilling of intervals that are large and have few uses, and
+      // discourages spilling of small intervals with many uses.
+      li.weight /= lis->getApproximateInstructionCount(li) * SlotIndex::NUM;
+    }
+  }
+  
+  return false;
+}
+
+/// Returns true if the given live interval is zero length.
+bool CalculateSpillWeights::isZeroLengthInterval(LiveInterval *li) const {
+  for (LiveInterval::Ranges::const_iterator
+       i = li->ranges.begin(), e = li->ranges.end(); i != e; ++i)
+    if (i->end.getPrevIndex() > i->start)
+      return false;
+  return true;
+}