Check in LLVM r95781.
diff --git a/lib/CodeGen/OptimizeExts.cpp b/lib/CodeGen/OptimizeExts.cpp
new file mode 100644
index 0000000..acb6869
--- /dev/null
+++ b/lib/CodeGen/OptimizeExts.cpp
@@ -0,0 +1,197 @@
+//===-- OptimizeExts.cpp - Optimize sign / zero extension instrs -----===//
+//
+// The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This pass performs optimization of sign / zero extension instructions. It
+// may be extended to handle other instructions of similar property.
+//
+// On some targets, some instructions, e.g. X86 sign / zero extension, may
+// leave the source value in the lower part of the result. This pass will
+// replace (some) uses of the pre-extension value with uses of the sub-register
+// of the results.
+//
+//===----------------------------------------------------------------------===//
+
+#define DEBUG_TYPE "ext-opt"
+#include "llvm/CodeGen/Passes.h"
+#include "llvm/CodeGen/MachineDominators.h"
+#include "llvm/CodeGen/MachineInstrBuilder.h"
+#include "llvm/CodeGen/MachineRegisterInfo.h"
+#include "llvm/Target/TargetInstrInfo.h"
+#include "llvm/Target/TargetRegisterInfo.h"
+#include "llvm/Support/CommandLine.h"
+#include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/ADT/Statistic.h"
+using namespace llvm;
+
+static cl::opt<bool> Aggressive("aggressive-ext-opt", cl::Hidden,
+ cl::desc("Aggressive extension optimization"));
+
+STATISTIC(NumReuse, "Number of extension results reused");
+
+namespace {
+ class OptimizeExts : public MachineFunctionPass {
+ const TargetMachine *TM;
+ const TargetInstrInfo *TII;
+ MachineRegisterInfo *MRI;
+ MachineDominatorTree *DT; // Machine dominator tree
+
+ public:
+ static char ID; // Pass identification
+ OptimizeExts() : MachineFunctionPass(&ID) {}
+
+ virtual bool runOnMachineFunction(MachineFunction &MF);
+
+ virtual void getAnalysisUsage(AnalysisUsage &AU) const {
+ AU.setPreservesCFG();
+ MachineFunctionPass::getAnalysisUsage(AU);
+ if (Aggressive) {
+ AU.addRequired<MachineDominatorTree>();
+ AU.addPreserved<MachineDominatorTree>();
+ }
+ }
+
+ private:
+ bool OptimizeInstr(MachineInstr *MI, MachineBasicBlock *MBB,
+ SmallPtrSet<MachineInstr*, 8> &LocalMIs);
+ };
+}
+
+char OptimizeExts::ID = 0;
+static RegisterPass<OptimizeExts>
+X("opt-exts", "Optimize sign / zero extensions");
+
+FunctionPass *llvm::createOptimizeExtsPass() { return new OptimizeExts(); }
+
+/// OptimizeInstr - If instruction is a copy-like instruction, i.e. it reads
+/// a single register and writes a single register and it does not modify
+/// the source, and if the source value is preserved as a sub-register of
+/// the result, then replace all reachable uses of the source with the subreg
+/// of the result.
+bool OptimizeExts::OptimizeInstr(MachineInstr *MI, MachineBasicBlock *MBB,
+ SmallPtrSet<MachineInstr*, 8> &LocalMIs) {
+ bool Changed = false;
+ LocalMIs.insert(MI);
+
+ unsigned SrcReg, DstReg, SubIdx;
+ if (TII->isCoalescableExtInstr(*MI, SrcReg, DstReg, SubIdx)) {
+ if (TargetRegisterInfo::isPhysicalRegister(DstReg) ||
+ TargetRegisterInfo::isPhysicalRegister(SrcReg))
+ return false;
+
+ MachineRegisterInfo::use_iterator UI = MRI->use_begin(SrcReg);
+ if (++UI == MRI->use_end())
+ // No other uses.
+ return false;
+
+ // Ok, the source has other uses. See if we can replace the other uses
+ // with use of the result of the extension.
+ SmallPtrSet<MachineBasicBlock*, 4> ReachedBBs;
+ UI = MRI->use_begin(DstReg);
+ for (MachineRegisterInfo::use_iterator UE = MRI->use_end(); UI != UE;
+ ++UI)
+ ReachedBBs.insert(UI->getParent());
+
+ bool ExtendLife = true;
+ // Uses that are in the same BB of uses of the result of the instruction.
+ SmallVector<MachineOperand*, 8> Uses;
+ // Uses that the result of the instruction can reach.
+ SmallVector<MachineOperand*, 8> ExtendedUses;
+
+ UI = MRI->use_begin(SrcReg);
+ for (MachineRegisterInfo::use_iterator UE = MRI->use_end(); UI != UE;
+ ++UI) {
+ MachineOperand &UseMO = UI.getOperand();
+ MachineInstr *UseMI = &*UI;
+ if (UseMI == MI)
+ continue;
+ if (UseMI->isPHI()) {
+ ExtendLife = false;
+ continue;
+ }
+
+ MachineBasicBlock *UseMBB = UseMI->getParent();
+ if (UseMBB == MBB) {
+ // Local uses that come after the extension.
+ if (!LocalMIs.count(UseMI))
+ Uses.push_back(&UseMO);
+ } else if (ReachedBBs.count(UseMBB))
+ // Non-local uses where the result of extension is used. Always
+ // replace these unless it's a PHI.
+ Uses.push_back(&UseMO);
+ else if (Aggressive && DT->dominates(MBB, UseMBB))
+ // We may want to extend live range of the extension result in order
+ // to replace these uses.
+ ExtendedUses.push_back(&UseMO);
+ else {
+ // Both will be live out of the def MBB anyway. Don't extend live
+ // range of the extension result.
+ ExtendLife = false;
+ break;
+ }
+ }
+
+ if (ExtendLife && !ExtendedUses.empty())
+ // Ok, we'll extend the liveness of the extension result.
+ std::copy(ExtendedUses.begin(), ExtendedUses.end(),
+ std::back_inserter(Uses));
+
+ // Now replace all uses.
+ if (!Uses.empty()) {
+ SmallPtrSet<MachineBasicBlock*, 4> PHIBBs;
+ // Look for PHI uses of the extended result, we don't want to extend the
+ // liveness of a PHI input. It breaks all kinds of assumptions down
+ // stream. A PHI use is expected to be the kill of its source values.
+ UI = MRI->use_begin(DstReg);
+ for (MachineRegisterInfo::use_iterator UE = MRI->use_end(); UI != UE;
+ ++UI)
+ if (UI->isPHI())
+ PHIBBs.insert(UI->getParent());
+
+ const TargetRegisterClass *RC = MRI->getRegClass(SrcReg);
+ for (unsigned i = 0, e = Uses.size(); i != e; ++i) {
+ MachineOperand *UseMO = Uses[i];
+ MachineInstr *UseMI = UseMO->getParent();
+ MachineBasicBlock *UseMBB = UseMI->getParent();
+ if (PHIBBs.count(UseMBB))
+ continue;
+ unsigned NewVR = MRI->createVirtualRegister(RC);
+ BuildMI(*UseMBB, UseMI, UseMI->getDebugLoc(),
+ TII->get(TargetOpcode::EXTRACT_SUBREG), NewVR)
+ .addReg(DstReg).addImm(SubIdx);
+ UseMO->setReg(NewVR);
+ ++NumReuse;
+ Changed = true;
+ }
+ }
+ }
+
+ return Changed;
+}
+
+bool OptimizeExts::runOnMachineFunction(MachineFunction &MF) {
+ TM = &MF.getTarget();
+ TII = TM->getInstrInfo();
+ MRI = &MF.getRegInfo();
+ DT = Aggressive ? &getAnalysis<MachineDominatorTree>() : 0;
+
+ bool Changed = false;
+
+ SmallPtrSet<MachineInstr*, 8> LocalMIs;
+ for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I) {
+ MachineBasicBlock *MBB = &*I;
+ LocalMIs.clear();
+ for (MachineBasicBlock::iterator MII = I->begin(), ME = I->end(); MII != ME;
+ ++MII) {
+ MachineInstr *MI = &*MII;
+ Changed |= OptimizeInstr(MI, MBB, LocalMIs);
+ }
+ }
+
+ return Changed;
+}