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
25 typedef DenseMap<unsigned, MachineBasicBlock*> PHIDefMap;
29 static char ID; // Pass identification, replacement for typeid
30 PHIElimination() : MachineFunctionPass(&ID) {}
32 virtual bool runOnMachineFunction(MachineFunction &Fn);
34 virtual void getAnalysisUsage(AnalysisUsage &AU) const;
36 /// Return true if the given vreg was defined by a PHI intsr prior to
38 bool hasPHIDef(unsigned vreg) const {
39 return PHIDefs.count(vreg);
43 /// EliminatePHINodes - Eliminate phi nodes by inserting copy instructions
44 /// in predecessor basic blocks.
46 bool EliminatePHINodes(MachineFunction &MF, MachineBasicBlock &MBB);
47 void LowerAtomicPHINode(MachineBasicBlock &MBB,
48 MachineBasicBlock::iterator AfterPHIsIt);
50 /// analyzePHINodes - Gather information about the PHI nodes in
51 /// here. In particular, we want to map the number of uses of a virtual
52 /// register which is used in a PHI node. We map that to the BB the
53 /// vreg is coming from. This is used later to determine when the vreg
54 /// is killed in the BB.
56 void analyzePHINodes(const MachineFunction& Fn);
58 /// Split critical edges where necessary for good coalescer performance.
59 bool SplitPHIEdges(MachineFunction &MF, MachineBasicBlock &MBB,
62 /// SplitCriticalEdge - Split a critical edge from A to B by
63 /// inserting a new MBB. Update branches in A and PHI instructions
64 /// in B. Return the new block.
65 MachineBasicBlock *SplitCriticalEdge(MachineBasicBlock *A,
66 MachineBasicBlock *B);
68 /// FindCopyInsertPoint - Find a safe place in MBB to insert a copy from
69 /// SrcReg when following the CFG edge to SuccMBB. This needs to be after
70 /// any def of SrcReg, but before any subsequent point where control flow
71 /// might jump out of the basic block.
72 MachineBasicBlock::iterator FindCopyInsertPoint(MachineBasicBlock &MBB,
73 MachineBasicBlock &SuccMBB,
76 // SkipPHIsAndLabels - Copies need to be inserted after phi nodes and
77 // also after any exception handling labels: in landing pads execution
78 // starts at the label, so any copies placed before it won't be executed!
79 // We also deal with DBG_VALUEs, which are a bit tricky:
83 // Here the DBG_VALUE needs to be skipped, and if it refers to a PHI it
84 // needs to be annulled or, better, moved to follow the label, as well.
88 // Here it is not a good idea to skip the DBG_VALUE.
89 // FIXME: For now we skip and annul all DBG_VALUEs, maximally simple and
91 MachineBasicBlock::iterator SkipPHIsAndLabels(MachineBasicBlock &MBB,
92 MachineBasicBlock::iterator I) {
93 // Rather than assuming that EH labels come before other kinds of labels,
94 // just skip all labels.
95 while (I != MBB.end() &&
96 (I->isPHI() || I->isLabel() || I->isDebugValue())) {
97 if (I->isDebugValue() && I->getNumOperands()==3 &&
98 I->getOperand(0).isReg())
99 I->getOperand(0).setReg(0U);
105 typedef std::pair<unsigned, unsigned> BBVRegPair;
106 typedef DenseMap<BBVRegPair, unsigned> VRegPHIUse;
108 VRegPHIUse VRegPHIUseCount;
111 // Defs of PHI sources which are implicit_def.
112 SmallPtrSet<MachineInstr*, 4> ImpDefs;
114 // Lowered PHI nodes may be reused. We provide special DenseMap traits to
115 // match PHI nodes with identical arguments.
116 struct PHINodeTraits : public DenseMapInfo<MachineInstr*> {
117 static unsigned getHashValue(const MachineInstr *PtrVal);
118 static bool isEqual(const MachineInstr *LHS, const MachineInstr *RHS);
121 // Map reusable lowered PHI node -> incoming join register.
122 typedef DenseMap<MachineInstr*, unsigned, PHINodeTraits> LoweredPHIMap;
123 LoweredPHIMap LoweredPHIs;
128 #endif /* LLVM_CODEGEN_PHIELIMINATION_HPP */