1 //===-- lib/CodeGen/PHIElimination.h ----------------------------*- C++ -*-===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 #ifndef LLVM_CODEGEN_PHIELIMINATION_HPP
11 #define LLVM_CODEGEN_PHIELIMINATION_HPP
13 #include "llvm/ADT/DenseMap.h"
14 #include "llvm/ADT/SmallSet.h"
15 #include "llvm/ADT/SmallPtrSet.h"
16 #include "llvm/CodeGen/MachineFunctionPass.h"
17 #include "llvm/CodeGen/MachineRegisterInfo.h"
22 /// Lower PHI instructions to copies.
23 class PHIElimination : public MachineFunctionPass {
24 MachineRegisterInfo *MRI; // Machine register information
27 typedef SmallSet<MachineBasicBlock*, 4> PHIKillList;
28 typedef DenseMap<unsigned, PHIKillList> PHIKillMap;
29 typedef DenseMap<unsigned, MachineBasicBlock*> PHIDefMap;
33 typedef PHIKillList::iterator phi_kill_iterator;
34 typedef PHIKillList::const_iterator const_phi_kill_iterator;
36 static char ID; // Pass identification, replacement for typeid
37 PHIElimination() : MachineFunctionPass(&ID) {}
39 virtual bool runOnMachineFunction(MachineFunction &Fn);
41 virtual void getAnalysisUsage(AnalysisUsage &AU) const;
43 /// Return true if the given vreg was defined by a PHI intsr prior to
45 bool hasPHIDef(unsigned vreg) const {
46 return PHIDefs.count(vreg);
49 /// Returns the block in which the PHI instruction which defined the
50 /// given vreg used to reside.
51 MachineBasicBlock* getPHIDefBlock(unsigned vreg) {
52 PHIDefMap::iterator phiDefItr = PHIDefs.find(vreg);
53 assert(phiDefItr != PHIDefs.end() && "vreg has no phi-def.");
54 return phiDefItr->second;
57 /// Returns true if the given vreg was killed by a PHI instr.
58 bool hasPHIKills(unsigned vreg) const {
59 return PHIKills.count(vreg);
62 /// Returns an iterator over the BasicBlocks which contained PHI
63 /// kills of this register prior to lowering.
64 phi_kill_iterator phiKillsBegin(unsigned vreg) {
65 PHIKillMap::iterator phiKillItr = PHIKills.find(vreg);
66 assert(phiKillItr != PHIKills.end() && "vreg has no phi-kills.");
67 return phiKillItr->second.begin();
69 phi_kill_iterator phiKillsEnd(unsigned vreg) {
70 PHIKillMap::iterator phiKillItr = PHIKills.find(vreg);
71 assert(phiKillItr != PHIKills.end() && "vreg has no phi-kills.");
72 return phiKillItr->second.end();
76 /// EliminatePHINodes - Eliminate phi nodes by inserting copy instructions
77 /// in predecessor basic blocks.
79 bool EliminatePHINodes(MachineFunction &MF, MachineBasicBlock &MBB);
80 void LowerAtomicPHINode(MachineBasicBlock &MBB,
81 MachineBasicBlock::iterator AfterPHIsIt);
83 /// analyzePHINodes - Gather information about the PHI nodes in
84 /// here. In particular, we want to map the number of uses of a virtual
85 /// register which is used in a PHI node. We map that to the BB the
86 /// vreg is coming from. This is used later to determine when the vreg
87 /// is killed in the BB.
89 void analyzePHINodes(const MachineFunction& Fn);
91 /// Split critical edges where necessary for good coalescer performance.
92 bool SplitPHIEdges(MachineFunction &MF, MachineBasicBlock &MBB,
95 /// SplitCriticalEdge - Split a critical edge from A to B by
96 /// inserting a new MBB. Update branches in A and PHI instructions
97 /// in B. Return the new block.
98 MachineBasicBlock *SplitCriticalEdge(MachineBasicBlock *A,
99 MachineBasicBlock *B);
101 /// FindCopyInsertPoint - Find a safe place in MBB to insert a copy from
102 /// SrcReg when following the CFG edge to SuccMBB. This needs to be after
103 /// any def of SrcReg, but before any subsequent point where control flow
104 /// might jump out of the basic block.
105 MachineBasicBlock::iterator FindCopyInsertPoint(MachineBasicBlock &MBB,
106 MachineBasicBlock &SuccMBB,
109 // SkipPHIsAndLabels - Copies need to be inserted after phi nodes and
110 // also after any exception handling labels: in landing pads execution
111 // starts at the label, so any copies placed before it won't be executed!
112 // We also deal with DBG_VALUEs, which are a bit tricky:
116 // Here the DBG_VALUE needs to be skipped, and if it refers to a PHI it
117 // needs to be annulled or, better, moved to follow the label, as well.
121 // Here it is not a good idea to skip the DBG_VALUE.
122 // FIXME: For now we skip and annul all DBG_VALUEs, maximally simple and
124 MachineBasicBlock::iterator SkipPHIsAndLabels(MachineBasicBlock &MBB,
125 MachineBasicBlock::iterator I) {
126 // Rather than assuming that EH labels come before other kinds of labels,
127 // just skip all labels.
128 while (I != MBB.end() &&
129 (I->isPHI() || I->isLabel() || I->isDebugValue())) {
130 if (I->isDebugValue() && I->getNumOperands()==3 &&
131 I->getOperand(0).isReg())
132 I->getOperand(0).setReg(0U);
138 typedef std::pair<unsigned, unsigned> BBVRegPair;
139 typedef DenseMap<BBVRegPair, unsigned> VRegPHIUse;
141 VRegPHIUse VRegPHIUseCount;
145 // Defs of PHI sources which are implicit_def.
146 SmallPtrSet<MachineInstr*, 4> ImpDefs;
148 // Lowered PHI nodes may be reused. We provide special DenseMap traits to
149 // match PHI nodes with identical arguments.
150 struct PHINodeTraits : public DenseMapInfo<MachineInstr*> {
151 static unsigned getHashValue(const MachineInstr *PtrVal);
152 static bool isEqual(const MachineInstr *LHS, const MachineInstr *RHS);
155 // Map reusable lowered PHI node -> incoming join register.
156 typedef DenseMap<MachineInstr*, unsigned, PHINodeTraits> LoweredPHIMap;
157 LoweredPHIMap LoweredPHIs;
162 #endif /* LLVM_CODEGEN_PHIELIMINATION_HPP */