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
diff --git a/lib/CodeGen/CalcSpillWeights.cpp b/lib/CodeGen/CalcSpillWeights.cpp
new file mode 100644
index 0000000..dcffb8a
--- /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 ®Int = 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;
+}