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