forked from OSchip/llvm-project
120 lines
4.7 KiB
C++
120 lines
4.7 KiB
C++
//===-- lib/CodeGen/PHIElimination.h ----------------------------*- C++ -*-===//
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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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#ifndef LLVM_CODEGEN_PHIELIMINATION_HPP
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#define LLVM_CODEGEN_PHIELIMINATION_HPP
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#include "llvm/ADT/DenseMap.h"
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#include "llvm/ADT/SmallSet.h"
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#include "llvm/ADT/SmallPtrSet.h"
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#include "llvm/CodeGen/MachineFunctionPass.h"
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#include "llvm/CodeGen/MachineRegisterInfo.h"
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namespace llvm {
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class LiveVariables;
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/// Lower PHI instructions to copies.
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class PHIElimination : public MachineFunctionPass {
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MachineRegisterInfo *MRI; // Machine register information
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public:
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static char ID; // Pass identification, replacement for typeid
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PHIElimination() : MachineFunctionPass(&ID) {}
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virtual bool runOnMachineFunction(MachineFunction &Fn);
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virtual void getAnalysisUsage(AnalysisUsage &AU) const;
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private:
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/// EliminatePHINodes - Eliminate phi nodes by inserting copy instructions
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/// in predecessor basic blocks.
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///
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bool EliminatePHINodes(MachineFunction &MF, MachineBasicBlock &MBB);
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void LowerAtomicPHINode(MachineBasicBlock &MBB,
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MachineBasicBlock::iterator AfterPHIsIt);
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/// analyzePHINodes - Gather information about the PHI nodes in
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/// here. In particular, we want to map the number of uses of a virtual
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/// register which is used in a PHI node. We map that to the BB the
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/// vreg is coming from. This is used later to determine when the vreg
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/// is killed in the BB.
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///
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void analyzePHINodes(const MachineFunction& Fn);
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/// Split critical edges where necessary for good coalescer performance.
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bool SplitPHIEdges(MachineFunction &MF, MachineBasicBlock &MBB,
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LiveVariables &LV);
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/// SplitCriticalEdge - Split a critical edge from A to B by
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/// inserting a new MBB. Update branches in A and PHI instructions
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/// in B. Return the new block.
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MachineBasicBlock *SplitCriticalEdge(MachineBasicBlock *A,
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MachineBasicBlock *B);
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/// FindCopyInsertPoint - Find a safe place in MBB to insert a copy from
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/// SrcReg when following the CFG edge to SuccMBB. This needs to be after
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/// any def of SrcReg, but before any subsequent point where control flow
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/// might jump out of the basic block.
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MachineBasicBlock::iterator FindCopyInsertPoint(MachineBasicBlock &MBB,
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MachineBasicBlock &SuccMBB,
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unsigned SrcReg);
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// SkipPHIsAndLabels - Copies need to be inserted after phi nodes and
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// also after any exception handling labels: in landing pads execution
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// starts at the label, so any copies placed before it won't be executed!
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// We also deal with DBG_VALUEs, which are a bit tricky:
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// PHI
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// DBG_VALUE
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// LABEL
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// Here the DBG_VALUE needs to be skipped, and if it refers to a PHI it
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// needs to be annulled or, better, moved to follow the label, as well.
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// PHI
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// DBG_VALUE
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// no label
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// Here it is not a good idea to skip the DBG_VALUE.
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// FIXME: For now we skip and annul all DBG_VALUEs, maximally simple and
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// maximally stupid.
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MachineBasicBlock::iterator SkipPHIsAndLabels(MachineBasicBlock &MBB,
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MachineBasicBlock::iterator I) {
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// Rather than assuming that EH labels come before other kinds of labels,
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// just skip all labels.
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while (I != MBB.end() &&
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(I->isPHI() || I->isLabel() || I->isDebugValue())) {
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if (I->isDebugValue() && I->getNumOperands()==3 &&
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I->getOperand(0).isReg())
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I->getOperand(0).setReg(0U);
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++I;
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}
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return I;
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}
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typedef std::pair<unsigned, unsigned> BBVRegPair;
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typedef DenseMap<BBVRegPair, unsigned> VRegPHIUse;
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VRegPHIUse VRegPHIUseCount;
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// Defs of PHI sources which are implicit_def.
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SmallPtrSet<MachineInstr*, 4> ImpDefs;
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// Lowered PHI nodes may be reused. We provide special DenseMap traits to
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// match PHI nodes with identical arguments.
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struct PHINodeTraits : public DenseMapInfo<MachineInstr*> {
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static unsigned getHashValue(const MachineInstr *PtrVal);
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static bool isEqual(const MachineInstr *LHS, const MachineInstr *RHS);
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};
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// Map reusable lowered PHI node -> incoming join register.
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typedef DenseMap<MachineInstr*, unsigned, PHINodeTraits> LoweredPHIMap;
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LoweredPHIMap LoweredPHIs;
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};
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}
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#endif /* LLVM_CODEGEN_PHIELIMINATION_HPP */
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