1 //===-- PHIEliminationUtils.cpp - Helper functions for PHI elimination ----===// 2 // 3 // The LLVM Compiler Infrastructure 4 // 5 // This file is distributed under the University of Illinois Open Source 6 // License. See LICENSE.TXT for details. 7 // 8 //===----------------------------------------------------------------------===// 9 10 #include "PHIEliminationUtils.h" 11 #include "llvm/ADT/SmallPtrSet.h" 12 #include "llvm/CodeGen/MachineBasicBlock.h" 13 #include "llvm/CodeGen/MachineFunction.h" 14 #include "llvm/CodeGen/MachineRegisterInfo.h" 15 using namespace llvm; 16 17 // findCopyInsertPoint - Find a safe place in MBB to insert a copy from SrcReg 18 // when following the CFG edge to SuccMBB. This needs to be after any def of 19 // SrcReg, but before any subsequent point where control flow might jump out of 20 // the basic block. 21 MachineBasicBlock::iterator 22 llvm::findPHICopyInsertPoint(MachineBasicBlock* MBB, MachineBasicBlock* SuccMBB, 23 unsigned SrcReg) { 24 // Handle the trivial case trivially. 25 if (MBB->empty()) 26 return MBB->begin(); 27 28 // Usually, we just want to insert the copy before the first terminator 29 // instruction. However, for the edge going to a landing pad, we must insert 30 // the copy before the call/invoke instruction. 31 if (!SuccMBB->isEHPad()) 32 return MBB->getFirstTerminator(); 33 34 // Discover any defs/uses in this basic block. 35 SmallPtrSet<MachineInstr*, 8> DefUsesInMBB; 36 MachineRegisterInfo& MRI = MBB->getParent()->getRegInfo(); 37 for (MachineInstr &RI : MRI.reg_instructions(SrcReg)) { 38 if (RI.getParent() == MBB) 39 DefUsesInMBB.insert(&RI); 40 } 41 42 MachineBasicBlock::iterator InsertPoint; 43 if (DefUsesInMBB.empty()) { 44 // No defs. Insert the copy at the start of the basic block. 45 InsertPoint = MBB->begin(); 46 } else if (DefUsesInMBB.size() == 1) { 47 // Insert the copy immediately after the def/use. 48 InsertPoint = *DefUsesInMBB.begin(); 49 ++InsertPoint; 50 } else { 51 // Insert the copy immediately after the last def/use. 52 InsertPoint = MBB->end(); 53 while (!DefUsesInMBB.count(&*--InsertPoint)) {} 54 ++InsertPoint; 55 } 56 57 // Make sure the copy goes after any phi nodes however. 58 return MBB->SkipPHIsAndLabels(InsertPoint); 59 } 60
