1 //===--------- BreakCriticalMachineEdges.h - Break critical edges ---------===//
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 // Helper function to break a critical machine edge.
12 //===---------------------------------------------------------------------===//
14 #ifndef LLVM_CODEGEN_BREAKCRITICALMACHINEEDGES_H
15 #define LLVM_CODEGEN_BREAKCRITICALMACHINEEDGES_H
17 #include "llvm/CodeGen/MachineJumpTableInfo.h"
18 #include "llvm/Target/TargetInstrInfo.h"
19 #include "llvm/Target/TargetMachine.h"
23 MachineBasicBlock* SplitCriticalMachineEdge(MachineBasicBlock* src,
24 MachineBasicBlock* dst) {
25 MachineFunction &MF = *src->getParent();
26 const BasicBlock* srcBB = src->getBasicBlock();
28 MachineBasicBlock* crit_mbb = MF.CreateMachineBasicBlock(srcBB);
30 // modify the llvm control flow graph
31 src->removeSuccessor(dst);
32 src->addSuccessor(crit_mbb);
33 crit_mbb->addSuccessor(dst);
35 // insert the new block into the machine function.
36 MF.push_back(crit_mbb);
38 // insert a unconditional branch linking the new block to dst
39 const TargetMachine& TM = MF.getTarget();
40 const TargetInstrInfo* TII = TM.getInstrInfo();
41 std::vector<MachineOperand> emptyConditions;
42 TII->InsertBranch(*crit_mbb, dst, (MachineBasicBlock*)0,
45 // modify every branch in src that points to dst to point to the new
46 // machine basic block instead:
47 MachineBasicBlock::iterator mii = src->end();
48 bool found_branch = false;
49 while (mii != src->begin()) {
51 // if there are no more branches, finish the loop
52 if (!mii->getDesc().isTerminator()) {
56 // Scan the operands of this branch, replacing any uses of dst with
58 for (unsigned i = 0, e = mii->getNumOperands(); i != e; ++i) {
59 MachineOperand & mo = mii->getOperand(i);
60 if (mo.isMBB() && mo.getMBB() == dst) {
67 // TODO: This is tentative. It may be necessary to fix this code. Maybe
68 // I am inserting too many gotos, but I am trusting that the asm printer
69 // will optimize the unnecessary gotos.
71 TII->InsertBranch(*src, crit_mbb, (MachineBasicBlock*)0,
75 /// Change all the phi functions in dst, so that the incoming block be
76 /// crit_mbb, instead of src
77 for(mii = dst->begin(); mii != dst->end(); mii++) {
78 /// the first instructions are always phi functions.
79 if(mii->getOpcode() != TargetInstrInfo::PHI)
82 // Find the operands corresponding to the source block
83 std::vector<unsigned> toRemove;
85 for (unsigned u = 0; u != mii->getNumOperands(); ++u)
86 if (mii->getOperand(u).isMBB() &&
87 mii->getOperand(u).getMBB() == src) {
88 reg = mii->getOperand(u-1).getReg();
89 toRemove.push_back(u-1);
91 // Remove all uses of this MBB
92 for (std::vector<unsigned>::reverse_iterator I = toRemove.rbegin(),
93 E = toRemove.rend(); I != E; ++I) {
94 mii->RemoveOperand(*I+1);
95 mii->RemoveOperand(*I);
98 // Add a single use corresponding to the new MBB
99 mii->addOperand(MachineOperand::CreateReg(reg, false));
100 mii->addOperand(MachineOperand::CreateMBB(crit_mbb));