Beginning SplitKit - utility classes for live range splitting.

This is a work in progress. So far we have some basic loop analysis to help determine where it is useful to split a live range around a loop. The actual loop splitting code from Splitter.cpp is also going to move in here. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@108842 91177308-0d34-0410-b5e6-96231b3b80d8
2026-04-20 00:20:11 +00:00 · 2010-07-20 15:41:07 +00:00
parent 26ede6834e
commit 8ae0263471
4 changed files with 261 additions and 1 deletions
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+//===---------- SplitKit.cpp - Toolkit for splitting live ranges ----------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file contains the SplitAnalysis class as well as mutator functions for
+// live range splitting.
+//
+//===----------------------------------------------------------------------===//
+
+#define DEBUG_TYPE "splitter"
+#include "SplitKit.h"
+#include "llvm/CodeGen/LiveIntervalAnalysis.h"
+#include "llvm/CodeGen/MachineFunctionPass.h"
+#include "llvm/CodeGen/MachineLoopInfo.h"
+#include "llvm/CodeGen/MachineRegisterInfo.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/raw_ostream.h"
+
+using namespace llvm;
+
+
+//===----------------------------------------------------------------------===//
+//                                 Split Analysis
+//===----------------------------------------------------------------------===//
+
+SplitAnalysis::SplitAnalysis(const MachineFunction *mf,
+                             const LiveIntervals *lis,
+                             const MachineLoopInfo *mli)
+  : mf_(*mf),
+    lis_(*lis),
+    loops_(*mli),
+    curli_(0) {}
+
+void SplitAnalysis::clear() {
+  usingInstrs_.clear();
+  usingBlocks_.clear();
+  usingLoops_.clear();
+}
+
+/// analyseUses - Count instructions, basic blocks, and loops using curli.
+void SplitAnalysis::analyseUses() {
+  const MachineRegisterInfo &MRI = mf_.getRegInfo();
+  for (MachineRegisterInfo::reg_iterator I = MRI.reg_begin(curli_->reg);
+       MachineInstr *MI = I.skipInstruction();) {
+    if (MI->isDebugValue() || !usingInstrs_.insert(MI))
+      continue;
+    MachineBasicBlock *MBB = MI->getParent();
+    if (usingBlocks_[MBB]++)
+      continue;
+    if (MachineLoop *Loop = loops_.getLoopFor(MBB))
+      usingLoops_.insert(Loop);
+  }
+  DEBUG(dbgs() << "Counted "
+               << usingInstrs_.size() << " instrs, "
+               << usingBlocks_.size() << " blocks, "
+               << usingLoops_.size()  << " loops in "
+               << *curli_ << "\n");
+}
+
+SplitAnalysis::LoopPeripheralUse
+SplitAnalysis::analyzeLoopPeripheralUse(const MachineLoop *Loop) {
+  // Peripheral blocks.
+  SmallVector<MachineBasicBlock*, 16> Peri;
+  Loop->getExitBlocks(Peri);
+  if (MachineBasicBlock *PredBB = Loop->getLoopPredecessor())
+    Peri.push_back(PredBB);
+  array_pod_sort(Peri.begin(), Peri.end());
+  Peri.erase(std::unique(Peri.begin(), Peri.end()), Peri.end());
+
+  LoopPeripheralUse use = ContainedInLoop;
+  for (BlockCountMap::iterator I = usingBlocks_.begin(), E = usingBlocks_.end();
+       I != E; ++I) {
+    const MachineBasicBlock *MBB = I->first;
+    // Is this a peripheral block?
+    if (use < MultiPeripheral &&
+        std::binary_search(Peri.begin(), Peri.end(), MBB)) {
+      if (I->second > 1) use = MultiPeripheral;
+      else               use = SinglePeripheral;
+      continue;
+    }
+    // Is it a loop block?
+    if (Loop->contains(MBB))
+      continue;
+    // It must be an unrelated block.
+    return OutsideLoop;
+  }
+  return use;
+}
+
+void SplitAnalysis::analyze(const LiveInterval *li) {
+  clear();
+  curli_ = li;
+  analyseUses();
+}
+
+const MachineLoop *SplitAnalysis::getBestSplitLoop() {
+  LoopPtrSet Loops, SecondLoops;
+
+  // Find first-class and second class candidate loops.
+  // We prefer to split around loops where curli is used outside the periphery.
+  for (LoopPtrSet::const_iterator I = usingLoops_.begin(),
+       E = usingLoops_.end(); I != E; ++I)
+    switch(analyzeLoopPeripheralUse(*I)) {
+    case OutsideLoop:
+      Loops.insert(*I);
+      break;
+    case MultiPeripheral:
+      SecondLoops.insert(*I);
+      break;
+    default:
+      continue;
+    }
+
+  // If there are no first class loops available, look at second class loops.
+  if (Loops.empty())
+    Loops = SecondLoops;
+
+  if (Loops.empty())
+    return 0;
+
+  // Pick the earliest loop.
+  // FIXME: Are there other heuristics to consider?
+  // - avoid breaking critical edges.
+  // - avoid impossible loops.
+  const MachineLoop *Best = 0;
+  SlotIndex BestIdx;
+  for (LoopPtrSet::const_iterator I = Loops.begin(), E = Loops.end(); I != E;
+       ++I) {
+    SlotIndex Idx = lis_.getMBBStartIdx((*I)->getHeader());
+    if (!Best || Idx < BestIdx)
+      Best = *I, BestIdx = Idx;
+  }
+  return Best;
+}
+
+//===----------------------------------------------------------------------===//
+//                               Loop Splitting
+//===----------------------------------------------------------------------===//
+
+bool llvm::splitAroundLoop(SplitAnalysis &sa, const MachineLoop *loop) {
+  return false;
+}
+