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3c2a4cc1bc
findPHICopyInsertPoint special cases placement in a block with a callbr or invoke in it. In that case, we must ensure that the copy is placed before the INLINEASM_BR or call instruction, if the register is defined prior to that instruction, because it may jump out of the block. Previously, the code placed it immediately after the last def _or use_. This is wrong, if the use is the instruction which may jump. We could correctly place it immediately after the last def (ignoring uses), but that is non-optimal for register pressure. Instead, place the copy after the last def, or before the call/inlineasm_br, whichever is later. Differential Revision: https://reviews.llvm.org/D87865
65 lines
2.5 KiB
C++
65 lines
2.5 KiB
C++
//===-- 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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