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//===-- PHIEliminationUtils.cpp - Helper functions for PHI elimination ----===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
#include "PHIEliminationUtils.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/CodeGen/MachineBasicBlock.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
using namespace llvm;
// 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
llvm::findPHICopyInsertPoint(MachineBasicBlock* MBB, MachineBasicBlock* SuccMBB,
unsigned SrcReg) {
// Handle the trivial case trivially.
if (MBB->empty())
return MBB->begin();
// Usually, we just want to insert the copy before the first terminator
// instruction. However, for the edge going to a landing pad, we must insert
// the copy before the call/invoke instruction.
if (!SuccMBB->isLandingPad())
return MBB->getFirstTerminator();
// Discover any defs/uses in this basic block.
SmallPtrSet<MachineInstr*, 8> DefUsesInMBB;
MachineRegisterInfo& MRI = MBB->getParent()->getRegInfo();
for (MachineRegisterInfo::reg_iterator RI = MRI.reg_begin(SrcReg),
RE = MRI.reg_end(); RI != RE; ++RI) {
MachineInstr* DefUseMI = &*RI;
if (DefUseMI->getParent() == MBB)
DefUsesInMBB.insert(DefUseMI);
}
MachineBasicBlock::iterator InsertPoint;
if (DefUsesInMBB.empty()) {
// No defs. Insert the copy at the start of the basic block.
InsertPoint = MBB->begin();
} else if (DefUsesInMBB.size() == 1) {
// Insert the copy immediately after the def/use.
InsertPoint = *DefUsesInMBB.begin();
++InsertPoint;
} else {
// Insert the copy immediately after the last def/use.
InsertPoint = MBB->end();
while (!DefUsesInMBB.count(&*--InsertPoint)) {}
++InsertPoint;
}
// Make sure the copy goes after any phi nodes however.
return MBB->SkipPHIsAndLabels(InsertPoint);
}
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