65 lines · cpp
1//===-- PHIEliminationUtils.cpp - Helper functions for PHI elimination ----===//2//3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.4// See https://llvm.org/LICENSE.txt for license information.5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception6//7//===----------------------------------------------------------------------===//8 9#include "PHIEliminationUtils.h"10#include "llvm/ADT/SmallPtrSet.h"11#include "llvm/CodeGen/MachineFunction.h"12#include "llvm/CodeGen/MachineRegisterInfo.h"13 14using namespace llvm;15 16// findCopyInsertPoint - Find a safe place in MBB to insert a copy from SrcReg17// when following the CFG edge to SuccMBB. This needs to be after any def of18// SrcReg, but before any subsequent point where control flow might jump out of19// the basic block.20MachineBasicBlock::iterator21llvm::findPHICopyInsertPoint(MachineBasicBlock* MBB, MachineBasicBlock* SuccMBB,22 Register SrcReg) {23 // Handle the trivial case trivially.24 if (MBB->empty())25 return MBB->begin();26 27 // Usually, we just want to insert the copy before the first terminator28 // instruction. However, for the edge going to a landing pad, we must insert29 // the copy before the call/invoke instruction. Similarly for an INLINEASM_BR30 // going to an indirect target. This is similar to SplitKit.cpp's31 // computeLastInsertPoint, and similarly assumes that there cannot be multiple32 // instructions that are Calls with EHPad successors or INLINEASM_BR in a33 // block.34 bool EHPadSuccessor = SuccMBB->isEHPad();35 if (!EHPadSuccessor && !SuccMBB->isInlineAsmBrIndirectTarget())36 return MBB->getFirstTerminator();37 38 // Discover any defs in this basic block.39 SmallPtrSet<MachineInstr *, 8> DefsInMBB;40 MachineRegisterInfo& MRI = MBB->getParent()->getRegInfo();41 for (MachineInstr &RI : MRI.def_instructions(SrcReg))42 if (RI.getParent() == MBB)43 DefsInMBB.insert(&RI);44 45 MachineBasicBlock::iterator InsertPoint = MBB->begin();46 // Insert the copy at the _latest_ point of:47 // 1. Immediately AFTER the last def48 // 2. Immediately BEFORE a call/inlineasm_br.49 for (auto I = MBB->rbegin(), E = MBB->rend(); I != E; ++I) {50 if (DefsInMBB.contains(&*I)) {51 InsertPoint = std::next(I.getReverse());52 break;53 }54 if ((EHPadSuccessor && I->isCall()) ||55 I->getOpcode() == TargetOpcode::INLINEASM_BR) {56 InsertPoint = I.getReverse();57 break;58 }59 }60 61 // Make sure the copy goes after any phi nodes but before62 // any debug nodes.63 return MBB->SkipPHIsAndLabels(InsertPoint);64}65