1 //===-- PHIEliminationUtils.cpp - Helper functions for PHI elimination ----===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 #include "PHIEliminationUtils.h"
11 #include "llvm/CodeGen/MachineBasicBlock.h"
12 #include "llvm/CodeGen/MachineFunction.h"
13 #include "llvm/CodeGen/MachineRegisterInfo.h"
14 #include "llvm/ADT/SmallPtrSet.h"
17 // findCopyInsertPoint - Find a safe place in MBB to insert a copy from SrcReg
18 // when following the CFG edge to SuccMBB. This needs to be after any def of
19 // SrcReg, but before any subsequent point where control flow might jump out of
21 MachineBasicBlock::iterator
22 llvm::findPHICopyInsertPoint(MachineBasicBlock* MBB, MachineBasicBlock* SuccMBB,
24 // Handle the trivial case trivially.
28 // Usually, we just want to insert the copy before the first terminator
29 // instruction. However, for the edge going to a landing pad, we must insert
30 // the copy before the call/invoke instruction.
31 if (!SuccMBB->isLandingPad())
32 return MBB->getFirstTerminator();
34 // Discover any defs/uses in this basic block.
35 SmallPtrSet<MachineInstr*, 8> DefUsesInMBB;
36 MachineRegisterInfo& MRI = MBB->getParent()->getRegInfo();
37 for (MachineRegisterInfo::reg_iterator RI = MRI.reg_begin(SrcReg),
38 RE = MRI.reg_end(); RI != RE; ++RI) {
39 MachineInstr* DefUseMI = &*RI;
40 if (DefUseMI->getParent() == MBB)
41 DefUsesInMBB.insert(DefUseMI);
44 MachineBasicBlock::iterator InsertPoint;
45 if (DefUsesInMBB.empty()) {
46 // No defs. Insert the copy at the start of the basic block.
47 InsertPoint = MBB->begin();
48 } else if (DefUsesInMBB.size() == 1) {
49 // Insert the copy immediately after the def/use.
50 InsertPoint = *DefUsesInMBB.begin();
53 // Insert the copy immediately after the last def/use.
54 InsertPoint = MBB->end();
55 while (!DefUsesInMBB.count(&*--InsertPoint)) {}
59 // Make sure the copy goes after any phi nodes however.
60 return MBB->SkipPHIsAndLabels(InsertPoint);