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