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/MachineBasicBlock.h"
17 #include "llvm/CodeGen/MachineFunctionPass.h"
21 class MachineRegisterInfo;
22 class MachineLoopInfo;
24 /// Lower PHI instructions to copies.
25 class PHIElimination : public MachineFunctionPass {
26 MachineRegisterInfo *MRI; // Machine register information
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;
37 /// EliminatePHINodes - Eliminate phi nodes by inserting copy instructions
38 /// in predecessor basic blocks.
40 bool EliminatePHINodes(MachineFunction &MF, MachineBasicBlock &MBB);
41 void LowerAtomicPHINode(MachineBasicBlock &MBB,
42 MachineBasicBlock::iterator AfterPHIsIt);
44 /// analyzePHINodes - Gather information about the PHI nodes in
45 /// here. In particular, we want to map the number of uses of a virtual
46 /// register which is used in a PHI node. We map that to the BB the
47 /// vreg is coming from. This is used later to determine when the vreg
48 /// is killed in the BB.
50 void analyzePHINodes(const MachineFunction& Fn);
52 /// Split critical edges where necessary for good coalescer performance.
53 bool SplitPHIEdges(MachineFunction &MF, MachineBasicBlock &MBB,
54 LiveVariables &LV, MachineLoopInfo *MLI);
56 /// SplitCriticalEdge - Split a critical edge from A to B by
57 /// inserting a new MBB. Update branches in A and PHI instructions
58 /// in B. Return the new block.
59 MachineBasicBlock *SplitCriticalEdge(MachineBasicBlock *A,
60 MachineBasicBlock *B);
62 /// FindCopyInsertPoint - Find a safe place in MBB to insert a copy from
63 /// SrcReg when following the CFG edge to SuccMBB. This needs to be after
64 /// any def of SrcReg, but before any subsequent point where control flow
65 /// might jump out of the basic block.
66 MachineBasicBlock::iterator FindCopyInsertPoint(MachineBasicBlock &MBB,
67 MachineBasicBlock &SuccMBB,
70 // SkipPHIsAndLabels - Copies need to be inserted after phi nodes and
71 // also after any exception handling labels: in landing pads execution
72 // starts at the label, so any copies placed before it won't be executed!
73 // We also deal with DBG_VALUEs, which are a bit tricky:
77 // Here the DBG_VALUE needs to be skipped, and if it refers to a PHI it
78 // needs to be annulled or, better, moved to follow the label, as well.
82 // Here it is not a good idea to skip the DBG_VALUE.
83 // FIXME: For now we skip and annul all DBG_VALUEs, maximally simple and
85 MachineBasicBlock::iterator SkipPHIsAndLabels(MachineBasicBlock &MBB,
86 MachineBasicBlock::iterator I) {
87 // Rather than assuming that EH labels come before other kinds of labels,
88 // just skip all labels.
89 while (I != MBB.end() &&
90 (I->isPHI() || I->isLabel() || I->isDebugValue())) {
91 if (I->isDebugValue() && I->getNumOperands()==3 &&
92 I->getOperand(0).isReg())
93 I->getOperand(0).setReg(0U);
99 typedef std::pair<unsigned, unsigned> BBVRegPair;
100 typedef DenseMap<BBVRegPair, unsigned> VRegPHIUse;
102 VRegPHIUse VRegPHIUseCount;
104 // Defs of PHI sources which are implicit_def.
105 SmallPtrSet<MachineInstr*, 4> ImpDefs;
107 // Map reusable lowered PHI node -> incoming join register.
108 typedef DenseMap<MachineInstr*, unsigned,
109 MachineInstrExpressionTrait> LoweredPHIMap;
110 LoweredPHIMap LoweredPHIs;
115 #endif /* LLVM_CODEGEN_PHIELIMINATION_HPP */