347 lines
12 KiB
C++
347 lines
12 KiB
C++
//===- MachineCopyPropagation.cpp - Machine Copy Propagation Pass ---------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This is an extremely simple MachineInstr-level copy propagation pass.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/CodeGen/Passes.h"
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#include "llvm/ADT/DenseMap.h"
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#include "llvm/ADT/SetVector.h"
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#include "llvm/ADT/SmallVector.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/CodeGen/MachineFunction.h"
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#include "llvm/CodeGen/MachineFunctionPass.h"
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#include "llvm/CodeGen/MachineRegisterInfo.h"
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#include "llvm/Pass.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Support/ErrorHandling.h"
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#include "llvm/Support/raw_ostream.h"
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#include "llvm/Target/TargetInstrInfo.h"
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#include "llvm/Target/TargetRegisterInfo.h"
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#include "llvm/Target/TargetSubtargetInfo.h"
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using namespace llvm;
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#define DEBUG_TYPE "codegen-cp"
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STATISTIC(NumDeletes, "Number of dead copies deleted");
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namespace {
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class MachineCopyPropagation : public MachineFunctionPass {
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const TargetRegisterInfo *TRI;
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const TargetInstrInfo *TII;
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MachineRegisterInfo *MRI;
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public:
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static char ID; // Pass identification, replacement for typeid
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MachineCopyPropagation() : MachineFunctionPass(ID) {
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initializeMachineCopyPropagationPass(*PassRegistry::getPassRegistry());
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}
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bool runOnMachineFunction(MachineFunction &MF) override;
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private:
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typedef SmallVector<unsigned, 4> DestList;
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typedef DenseMap<unsigned, DestList> SourceMap;
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void SourceNoLongerAvailable(unsigned Reg,
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SourceMap &SrcMap,
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DenseMap<unsigned, MachineInstr*> &AvailCopyMap);
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bool CopyPropagateBlock(MachineBasicBlock &MBB);
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};
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}
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char MachineCopyPropagation::ID = 0;
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char &llvm::MachineCopyPropagationID = MachineCopyPropagation::ID;
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INITIALIZE_PASS(MachineCopyPropagation, "machine-cp",
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"Machine Copy Propagation Pass", false, false)
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void
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MachineCopyPropagation::SourceNoLongerAvailable(unsigned Reg,
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SourceMap &SrcMap,
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DenseMap<unsigned, MachineInstr*> &AvailCopyMap) {
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for (MCRegAliasIterator AI(Reg, TRI, true); AI.isValid(); ++AI) {
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SourceMap::iterator SI = SrcMap.find(*AI);
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if (SI != SrcMap.end()) {
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const DestList& Defs = SI->second;
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for (DestList::const_iterator I = Defs.begin(), E = Defs.end();
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I != E; ++I) {
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unsigned MappedDef = *I;
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// Source of copy is no longer available for propagation.
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AvailCopyMap.erase(MappedDef);
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for (MCSubRegIterator SR(MappedDef, TRI); SR.isValid(); ++SR)
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AvailCopyMap.erase(*SR);
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}
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}
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}
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}
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static bool NoInterveningSideEffect(const MachineInstr *CopyMI,
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const MachineInstr *MI) {
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const MachineBasicBlock *MBB = CopyMI->getParent();
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if (MI->getParent() != MBB)
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return false;
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MachineBasicBlock::const_iterator I = CopyMI;
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MachineBasicBlock::const_iterator E = MBB->end();
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MachineBasicBlock::const_iterator E2 = MI;
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++I;
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while (I != E && I != E2) {
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if (I->hasUnmodeledSideEffects() || I->isCall() ||
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I->isTerminator())
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return false;
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++I;
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}
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return true;
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}
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/// isNopCopy - Return true if the specified copy is really a nop. That is
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/// if the source of the copy is the same of the definition of the copy that
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/// supplied the source. If the source of the copy is a sub-register than it
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/// must check the sub-indices match. e.g.
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/// ecx = mov eax
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/// al = mov cl
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/// But not
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/// ecx = mov eax
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/// al = mov ch
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static bool isNopCopy(MachineInstr *CopyMI, unsigned Def, unsigned Src,
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const TargetRegisterInfo *TRI) {
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unsigned SrcSrc = CopyMI->getOperand(1).getReg();
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if (Def == SrcSrc)
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return true;
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if (TRI->isSubRegister(SrcSrc, Def)) {
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unsigned SrcDef = CopyMI->getOperand(0).getReg();
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unsigned SubIdx = TRI->getSubRegIndex(SrcSrc, Def);
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if (!SubIdx)
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return false;
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return SubIdx == TRI->getSubRegIndex(SrcDef, Src);
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}
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return false;
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}
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bool MachineCopyPropagation::CopyPropagateBlock(MachineBasicBlock &MBB) {
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SmallSetVector<MachineInstr*, 8> MaybeDeadCopies; // Candidates for deletion
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DenseMap<unsigned, MachineInstr*> AvailCopyMap; // Def -> available copies map
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DenseMap<unsigned, MachineInstr*> CopyMap; // Def -> copies map
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SourceMap SrcMap; // Src -> Def map
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DEBUG(dbgs() << "MCP: CopyPropagateBlock " << MBB.getName() << "\n");
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bool Changed = false;
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for (MachineBasicBlock::iterator I = MBB.begin(), E = MBB.end(); I != E; ) {
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MachineInstr *MI = &*I;
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++I;
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if (MI->isCopy()) {
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unsigned Def = MI->getOperand(0).getReg();
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unsigned Src = MI->getOperand(1).getReg();
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if (TargetRegisterInfo::isVirtualRegister(Def) ||
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TargetRegisterInfo::isVirtualRegister(Src))
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report_fatal_error("MachineCopyPropagation should be run after"
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" register allocation!");
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DenseMap<unsigned, MachineInstr*>::iterator CI = AvailCopyMap.find(Src);
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if (CI != AvailCopyMap.end()) {
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MachineInstr *CopyMI = CI->second;
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if (!MRI->isReserved(Def) &&
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(!MRI->isReserved(Src) || NoInterveningSideEffect(CopyMI, MI)) &&
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isNopCopy(CopyMI, Def, Src, TRI)) {
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// The two copies cancel out and the source of the first copy
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// hasn't been overridden, eliminate the second one. e.g.
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// %ECX<def> = COPY %EAX<kill>
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// ... nothing clobbered EAX.
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// %EAX<def> = COPY %ECX
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// =>
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// %ECX<def> = COPY %EAX
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//
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// Also avoid eliminating a copy from reserved registers unless the
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// definition is proven not clobbered. e.g.
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// %RSP<def> = COPY %RAX
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// CALL
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// %RAX<def> = COPY %RSP
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DEBUG(dbgs() << "MCP: copy is a NOP, removing: "; MI->dump());
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// Clear any kills of Def between CopyMI and MI. This extends the
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// live range.
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for (MachineBasicBlock::iterator I = CopyMI, E = MI; I != E; ++I)
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I->clearRegisterKills(Def, TRI);
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MI->eraseFromParent();
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Changed = true;
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++NumDeletes;
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continue;
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}
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}
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// If Src is defined by a previous copy, it cannot be eliminated.
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for (MCRegAliasIterator AI(Src, TRI, true); AI.isValid(); ++AI) {
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CI = CopyMap.find(*AI);
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if (CI != CopyMap.end()) {
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DEBUG(dbgs() << "MCP: Copy is no longer dead: "; CI->second->dump());
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MaybeDeadCopies.remove(CI->second);
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}
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}
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DEBUG(dbgs() << "MCP: Copy is a deletion candidate: "; MI->dump());
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// Copy is now a candidate for deletion.
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MaybeDeadCopies.insert(MI);
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// If 'Src' is previously source of another copy, then this earlier copy's
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// source is no longer available. e.g.
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// %xmm9<def> = copy %xmm2
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// ...
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// %xmm2<def> = copy %xmm0
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// ...
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// %xmm2<def> = copy %xmm9
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SourceNoLongerAvailable(Def, SrcMap, AvailCopyMap);
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// Remember Def is defined by the copy.
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// ... Make sure to clear the def maps of aliases first.
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for (MCRegAliasIterator AI(Def, TRI, false); AI.isValid(); ++AI) {
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CopyMap.erase(*AI);
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AvailCopyMap.erase(*AI);
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}
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for (MCSubRegIterator SR(Def, TRI, /*IncludeSelf=*/true); SR.isValid();
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++SR) {
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CopyMap[*SR] = MI;
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AvailCopyMap[*SR] = MI;
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}
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// Remember source that's copied to Def. Once it's clobbered, then
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// it's no longer available for copy propagation.
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if (std::find(SrcMap[Src].begin(), SrcMap[Src].end(), Def) ==
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SrcMap[Src].end()) {
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SrcMap[Src].push_back(Def);
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}
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continue;
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}
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// Not a copy.
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SmallVector<unsigned, 2> Defs;
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int RegMaskOpNum = -1;
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for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
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MachineOperand &MO = MI->getOperand(i);
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if (MO.isRegMask())
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RegMaskOpNum = i;
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if (!MO.isReg())
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continue;
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unsigned Reg = MO.getReg();
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if (!Reg)
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continue;
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if (TargetRegisterInfo::isVirtualRegister(Reg))
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report_fatal_error("MachineCopyPropagation should be run after"
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" register allocation!");
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if (MO.isDef()) {
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Defs.push_back(Reg);
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continue;
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}
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// If 'Reg' is defined by a copy, the copy is no longer a candidate
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// for elimination.
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for (MCRegAliasIterator AI(Reg, TRI, true); AI.isValid(); ++AI) {
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DenseMap<unsigned, MachineInstr*>::iterator CI = CopyMap.find(*AI);
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if (CI != CopyMap.end()) {
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DEBUG(dbgs() << "MCP: Copy is used - not dead: "; CI->second->dump());
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MaybeDeadCopies.remove(CI->second);
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}
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}
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// Treat undef use like defs for copy propagation but not for
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// dead copy. We would need to do a liveness check to be sure the copy
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// is dead for undef uses.
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// The backends are allowed to do whatever they want with undef value
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// and we cannot be sure this register will not be rewritten to break
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// some false dependencies for the hardware for instance.
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if (MO.isUndef())
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Defs.push_back(Reg);
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}
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// The instruction has a register mask operand which means that it clobbers
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// a large set of registers. It is possible to use the register mask to
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// prune the available copies, but treat it like a basic block boundary for
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// now.
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if (RegMaskOpNum >= 0) {
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// Erase any MaybeDeadCopies whose destination register is clobbered.
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const MachineOperand &MaskMO = MI->getOperand(RegMaskOpNum);
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for (SmallSetVector<MachineInstr*, 8>::iterator
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DI = MaybeDeadCopies.begin(), DE = MaybeDeadCopies.end();
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DI != DE; ++DI) {
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unsigned Reg = (*DI)->getOperand(0).getReg();
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if (MRI->isReserved(Reg) || !MaskMO.clobbersPhysReg(Reg))
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continue;
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DEBUG(dbgs() << "MCP: Removing copy due to regmask clobbering: ";
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(*DI)->dump());
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(*DI)->eraseFromParent();
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Changed = true;
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++NumDeletes;
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}
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// Clear all data structures as if we were beginning a new basic block.
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MaybeDeadCopies.clear();
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AvailCopyMap.clear();
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CopyMap.clear();
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SrcMap.clear();
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continue;
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}
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for (unsigned i = 0, e = Defs.size(); i != e; ++i) {
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unsigned Reg = Defs[i];
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// No longer defined by a copy.
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for (MCRegAliasIterator AI(Reg, TRI, true); AI.isValid(); ++AI) {
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CopyMap.erase(*AI);
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AvailCopyMap.erase(*AI);
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}
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// If 'Reg' is previously source of a copy, it is no longer available for
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// copy propagation.
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SourceNoLongerAvailable(Reg, SrcMap, AvailCopyMap);
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}
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}
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// If MBB doesn't have successors, delete the copies whose defs are not used.
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// If MBB does have successors, then conservative assume the defs are live-out
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// since we don't want to trust live-in lists.
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if (MBB.succ_empty()) {
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for (SmallSetVector<MachineInstr*, 8>::iterator
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DI = MaybeDeadCopies.begin(), DE = MaybeDeadCopies.end();
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DI != DE; ++DI) {
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if (!MRI->isReserved((*DI)->getOperand(0).getReg())) {
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(*DI)->eraseFromParent();
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Changed = true;
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++NumDeletes;
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}
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}
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}
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return Changed;
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}
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bool MachineCopyPropagation::runOnMachineFunction(MachineFunction &MF) {
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if (skipOptnoneFunction(*MF.getFunction()))
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return false;
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bool Changed = false;
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TRI = MF.getSubtarget().getRegisterInfo();
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TII = MF.getSubtarget().getInstrInfo();
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MRI = &MF.getRegInfo();
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for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I)
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Changed |= CopyPropagateBlock(*I);
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return Changed;
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}
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