Dear guys,
I am having problem to split edges correctly. Mostly because the new
basic blocks are creating infinite loops. Could someone help me fixing the
code below? It is creating assembly like this one below. Block LBB1_9 was
inserted to break the critical edge between blocks LBB1_3 and LBB1_8. But
it changes the semantics of the original program, because, before, LBB1_8
was falling through LBB1_4, and now it is falling on LBB1_9.
LBB1_3: ;no_exit
lis r4, 21845
ori r4, r4, 21846
mulhw r4, r2, r4
addi r5, r2, -1
li r6, -1
srwi r6, r4, 31
add r4, r4, r6
mulli r4, r4, 3
li r6, 1
subf r2, r4, r2
cmpwi cr0, r2, 0
beq cr0, LBB1_9 ;no_exit
LBB1_7: ;no_exit
mr r2, r6
LBB1_8: ;no_exit
cmpwi cr0, r5, 0
add r2, r2, r3
bgt cr0, LBB1_5 ;no_exit.no_exit_llvm_crit_edge
LBB1_9: ;no_exit
mr r2, r6
b LBB1_8 ;no_exit
LBB1_4: ;no_exit.loopexit_llvm_crit_edge
The code is this one below:
void CriticalEdgeRemoval_Fer::split_critical_edge
(MachineBasicBlock & src, MachineBasicBlock & dst, MachineFunction
&
mf) {
const BasicBlock * src_bb = src.getBasicBlock();
MachineBasicBlock * crit_mbb = new MachineBasicBlock(src_bb);
/// modify the llvm control flow graph
src.addSuccessor(crit_mbb);
crit_mbb->addSuccessor(& dst);
src.removeSuccessor(& dst);
/// insert the new block into the machine function.
ilist<MachineBasicBlock>::iterator mbb_it = mf.getLastBlock();
++mbb_it;
mf.getBasicBlockList().insert(mbb_it, crit_mbb);
/// insert a unconditional branch linking the new block to dst
const TargetMachine & tm = mf.getTarget();
const TargetInstrInfo * tii = tm.getInstrInfo();
tii->insertGoto(*crit_mbb, dst);
/// modify every branch in src that points to dst to point to the new
/// machine basic block instead:
MachineBasicBlock::iterator mii = src.end();
while (mii != src.begin()) {
mii--;
// if there is not more branches, finish the loop
if (!tii->isTerminatorInstr(mii->getOpcode())) {
break;
}
// Scan the operands of this machine instruction, replacing any
// use of dst with crit_mbb.
for (unsigned i = 0, e = mii->getNumOperands(); i != e; ++i) {
if (mii->getOperand(i).isMachineBasicBlock() &&
mii->getOperand(i).getMachineBasicBlock() == & dst) {
mii->getOperand(i).setMachineBasicBlock(crit_mbb);
}
}
}
}
The problem is that you are inserting block 9 in the wrong spot. mf.getLastBlock() returns the block with the greatest number which may have nothing to do with the ordering. Why not use the end iterator (mf.end) to insert? -Tanya On Sat, 8 Jul 2006, Fernando Magno Quintao Pereira wrote:> > Dear guys, > > I am having problem to split edges correctly. Mostly because the new > basic blocks are creating infinite loops. Could someone help me fixing the > code below? It is creating assembly like this one below. Block LBB1_9 was > inserted to break the critical edge between blocks LBB1_3 and LBB1_8. But > it changes the semantics of the original program, because, before, LBB1_8 > was falling through LBB1_4, and now it is falling on LBB1_9. > > LBB1_3: ;no_exit > lis r4, 21845 > ori r4, r4, 21846 > mulhw r4, r2, r4 > addi r5, r2, -1 > li r6, -1 > srwi r6, r4, 31 > add r4, r4, r6 > mulli r4, r4, 3 > li r6, 1 > subf r2, r4, r2 > cmpwi cr0, r2, 0 > beq cr0, LBB1_9 ;no_exit > LBB1_7: ;no_exit > mr r2, r6 > LBB1_8: ;no_exit > cmpwi cr0, r5, 0 > add r2, r2, r3 > bgt cr0, LBB1_5 ;no_exit.no_exit_llvm_crit_edge > LBB1_9: ;no_exit > mr r2, r6 > b LBB1_8 ;no_exit > LBB1_4: ;no_exit.loopexit_llvm_crit_edge > > The code is this one below: > > void CriticalEdgeRemoval_Fer::split_critical_edge > (MachineBasicBlock & src, MachineBasicBlock & dst, MachineFunction & > mf) { > > const BasicBlock * src_bb = src.getBasicBlock(); > MachineBasicBlock * crit_mbb = new MachineBasicBlock(src_bb); > > /// modify the llvm control flow graph > src.addSuccessor(crit_mbb); > crit_mbb->addSuccessor(& dst); > src.removeSuccessor(& dst); > > /// insert the new block into the machine function. > ilist<MachineBasicBlock>::iterator mbb_it = mf.getLastBlock(); > ++mbb_it; > mf.getBasicBlockList().insert(mbb_it, crit_mbb); > > /// insert a unconditional branch linking the new block to dst > const TargetMachine & tm = mf.getTarget(); > const TargetInstrInfo * tii = tm.getInstrInfo(); > tii->insertGoto(*crit_mbb, dst); > > /// modify every branch in src that points to dst to point to the new > /// machine basic block instead: > MachineBasicBlock::iterator mii = src.end(); > while (mii != src.begin()) { > mii--; > // if there is not more branches, finish the loop > if (!tii->isTerminatorInstr(mii->getOpcode())) { > break; > } > // Scan the operands of this machine instruction, replacing any > // use of dst with crit_mbb. > for (unsigned i = 0, e = mii->getNumOperands(); i != e; ++i) { > if (mii->getOperand(i).isMachineBasicBlock() && > mii->getOperand(i).getMachineBasicBlock() == & dst) { > mii->getOperand(i).setMachineBasicBlock(crit_mbb); > } > } > } > > } > _______________________________________________ > LLVM Developers mailing list > LLVMdev at cs.uiuc.edu http://llvm.cs.uiuc.edu > http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev >
Thank you, Tanya. It solved the problem! Thanks a lot. Fernando> > The problem is that you are inserting block 9 in the wrong spot. > mf.getLastBlock() returns the block with the greatest number which may > have nothing to do with the ordering. Why not use the end iterator > (mf.end) to insert? > > -Tanya > > On Sat, 8 Jul 2006, Fernando Magno Quintao Pereira wrote: > > > > > Dear guys, > > > > I am having problem to split edges correctly. Mostly because the new > > basic blocks are creating infinite loops. Could someone help me fixing the > > code below? It is creating assembly like this one below. Block LBB1_9 was > > inserted to break the critical edge between blocks LBB1_3 and LBB1_8. But > > it changes the semantics of the original program, because, before, LBB1_8 > > was falling through LBB1_4, and now it is falling on LBB1_9.