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