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ed3a815136
When a phi node is finally lowered to a machine instruction it is important that the lowered "load" instruction is placed before the associated DEBUG_VALUE entry describing the value loaded. Renamed the existing SkipPHIsAndLabels to SkipPHIsLabelsAndDebug to more fully describe that it also skips debug entries. Then used the "new" function SkipPHIsAndLabels when the debug information should not be skipped when placing the lowered "load" instructions so that it is placed before the debug entries. Differential Revision: https://reviews.llvm.org/D23760 llvm-svn: 281727
61 lines
2.2 KiB
C++
61 lines
2.2 KiB
C++
//===-- PHIEliminationUtils.cpp - Helper functions for PHI elimination ----===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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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/MachineBasicBlock.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.
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if (!SuccMBB->isEHPad())
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return MBB->getFirstTerminator();
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// Discover any defs/uses in this basic block.
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SmallPtrSet<MachineInstr*, 8> DefUsesInMBB;
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MachineRegisterInfo& MRI = MBB->getParent()->getRegInfo();
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for (MachineInstr &RI : MRI.reg_instructions(SrcReg)) {
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if (RI.getParent() == MBB)
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DefUsesInMBB.insert(&RI);
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}
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MachineBasicBlock::iterator InsertPoint;
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if (DefUsesInMBB.empty()) {
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// No defs. Insert the copy at the start of the basic block.
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InsertPoint = MBB->begin();
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} else if (DefUsesInMBB.size() == 1) {
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// Insert the copy immediately after the def/use.
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InsertPoint = *DefUsesInMBB.begin();
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++InsertPoint;
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} else {
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// Insert the copy immediately after the last def/use.
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InsertPoint = MBB->end();
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while (!DefUsesInMBB.count(&*--InsertPoint)) {}
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++InsertPoint;
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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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