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//===-- PHIEliminationUtils.cpp - Helper functions for PHI elimination ----===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
#include "PHIEliminationUtils.h"
#include "llvm/ADT/SmallPtrSet.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. Similarly for an INLINEASM_BR
// going to an indirect target. This is similar to SplitKit.cpp's
// computeLastInsertPoint, and similarly assumes that there cannot be multiple
// instructions that are Calls with EHPad successors or INLINEASM_BR in a
// block.
bool EHPadSuccessor = SuccMBB->isEHPad();
if (!EHPadSuccessor && !SuccMBB->isInlineAsmBrIndirectTarget())
return MBB->getFirstTerminator();
// Discover any defs in this basic block.
SmallPtrSet<MachineInstr *, 8> DefsInMBB;
MachineRegisterInfo& MRI = MBB->getParent()->getRegInfo();
for (MachineInstr &RI : MRI.def_instructions(SrcReg))
if (RI.getParent() == MBB)
DefsInMBB.insert(&RI);
MachineBasicBlock::iterator InsertPoint = MBB->begin();
// Insert the copy at the _latest_ point of:
// 1. Immediately AFTER the last def
// 2. Immediately BEFORE a call/inlineasm_br.
for (auto I = MBB->rbegin(), E = MBB->rend(); I != E; ++I) {
if (DefsInMBB.contains(&*I)) {
InsertPoint = std::next(I.getReverse());
break;
}
if ((EHPadSuccessor && I->isCall()) ||
I->getOpcode() == TargetOpcode::INLINEASM_BR) {
InsertPoint = I.getReverse();
break;
}
}
// Make sure the copy goes after any phi nodes but before
// any debug nodes.
return MBB->SkipPHIsAndLabels(InsertPoint);
}
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