1 //===--------- BreakCriticalMachineEdges.h - Break critical edges ---------===//
3 // The LLVM Compiler Infrastructure
5 // This file was developed by Fernando Pereira and is distributed under
6 // the University of Illinois Open Source License. See LICENSE.TXT for details.
8 //===---------------------------------------------------------------------===//
10 // Helper function to break a critical machine edge.
12 //===---------------------------------------------------------------------===//
14 #ifndef LLVM_CODEGEN_ASMPRINTER_H
15 #define LLVM_CODEGEN_ASMPRINTER_H
17 #include "llvm/CodeGen/MachineInstr.h"
18 #include "llvm/CodeGen/MachineJumpTableInfo.h"
19 #include "llvm/Target/TargetInstrInfo.h"
20 #include "llvm/Target/TargetMachine.h"
21 #include "llvm/Support/Compiler.h"
25 MachineBasicBlock* SplitCriticalMachineEdge(MachineBasicBlock* src,
26 MachineBasicBlock* dst) {
27 const BasicBlock* srcBB = src->getBasicBlock();
29 MachineBasicBlock* crit_mbb = new MachineBasicBlock(srcBB);
31 // modify the llvm control flow graph
32 src->removeSuccessor(dst);
33 src->addSuccessor(crit_mbb);
34 crit_mbb->addSuccessor(dst);
36 // insert the new block into the machine function.
37 src->getParent()->getBasicBlockList().insert(src->getParent()->end(),
40 // insert a unconditional branch linking the new block to dst
41 const TargetMachine& TM = src->getParent()->getTarget();
42 const TargetInstrInfo* TII = TM.getInstrInfo();
43 std::vector<MachineOperand> emptyConditions;
44 TII->InsertBranch(*crit_mbb, dst, (MachineBasicBlock*)0, emptyConditions);
46 // modify every branch in src that points to dst to point to the new
47 // machine basic block instead:
48 MachineBasicBlock::iterator mii = src->end();
49 bool found_branch = false;
50 while (mii != src->begin()) {
52 // if there are no more branches, finish the loop
53 if (!TII->isTerminatorInstr(mii->getOpcode())) {
57 // Scan the operands of this branch, replacing any uses of dst with
59 for (unsigned i = 0, e = mii->getNumOperands(); i != e; ++i) {
60 MachineOperand & mo = mii->getOperand(i);
61 if (mo.isMachineBasicBlock() &&
62 mo.getMachineBasicBlock() == dst) {
64 mo.setMachineBasicBlock(crit_mbb);
69 // TODO: This is tentative. It may be necessary to fix this code. Maybe
70 // I am inserting too many gotos, but I am trusting that the asm printer
71 // will optimize the unnecessary gotos.
73 TII->InsertBranch(*src, crit_mbb, (MachineBasicBlock*)0, emptyConditions);
76 /// Change all the phi functions in dst, so that the incoming block be
77 /// crit_mbb, instead of src
78 for(mii = dst->begin(); mii != dst->end(); mii++) {
79 /// the first instructions are always phi functions.
80 if(mii->getOpcode() != TargetInstrInfo::PHI)
83 for (unsigned u = 0; u != mii->getNumOperands(); ++u)
84 if (mii->getOperand(u).isMachineBasicBlock() &&
85 mii->getOperand(u).getMachineBasicBlock() == src)
86 mii->getOperand(u).setMachineBasicBlock(crit_mbb);