On Aug 17, 2007, at 3:08 PM, Fernando Magno Quintao Pereira wrote:
>
> Thanks, Evan.
>
> Actually I've solved my problem with some hints from Dale and
> Anton.
Ok, cool. I didn't see their replies. Like I said, my email client is
acting funny.
> At least I think I've solved it. I had to add one method to
> TargetInstrInfo to tell me when an instruction is an indirect jump -
> TargetInstrInfo::tii.isIndirectJump(opcode). When that is the case, I
> update the jump table using:
>
> // Change jumps to go to the new basic block:
> if(isJumpTable) {
> mf.getJumpTableInfo()->ReplaceMBBInJumpTables(& dst,
> crit_mbb);
> }
>
> where dst was the old basic block, and crit_mbb is the new one,
> created to
> remove a critical edge. I think this should solve the problem. If you
> want, I can give you the pass to break critical edges of machine
> blocks,
> so that you guys can see if it is worth adding to LLVM's main
> branch. Up
> to now, as far as I know, there is no pass to remove critical edges of
> machine functions in LLVM.
Can you explain briefly what it does? What benefits do you expect?
>
> By the way, with this change, my register allocator is passing all the
> tests that LLVM with default RA (linearscan) is passing, although I am
> still using LLVM v1.8.
Very nice. Does this include all the external tests (specs, etc.)? Is
it possible for you to move to tot?
Evan
>
> best,
>
> Fernando
>
>> Sorry about the tardiness of my reply. My mail client has playing
>> tricks with me. :-)
>>
>> I am assuming the issue has nothing to do the branch to jumptable
>> instructions but rather the MachineJumpTableInfo associated with
>> every
>> MachineFunction? If so, please take a look at BranchFoldiing.cpp for
>> an example.
>>
>> Evan
>>
>> On Aug 10, 2007, at 12:30 PM, Fernando Magno Quintao Pereira wrote:
>>
>>>
>>> Hi all,
>>>
>>> I have a pass to break critical edges of Machine Basic Blocks,
>>> but I
>>> just discovered a bug (when compiling code for x86). The problem is
>>> 'jumpl
>>> *%reg'. I don't know how to update the jump table for this
type of
>>> instruction. The code that I had (see below) does not update the
>>> jump
>>> table, and the actual branch keeps jumping to the old basic block,
>>> instead
>>> of the new. Could someone help me to fix this? If it works fine,
>>> I can
>>> send a patch for this pass.
>>>
>>> /// modify every branch in src that points to dst to point
>>> /// to the new machine basic block "crit_mbb"
instead:
>>> MachineBasicBlock::iterator mii = src.end();
>>> bool found_branch = false;
>>> while (mii != src.begin()) {
>>> mii--;
>>> // if there are no more branches, finish the loop
>>> if (!tii->isTerminatorInstr(mii->getOpcode())) {
>>> break;
>>> }
>>> // Scan the operands of this branch, replacing any
>>> // uses 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) {
>>> found_branch = true;
>>>
mii->getOperand(i).setMachineBasicBlock(crit_mbb);
>>> }
>>> }
>>> }
>>>
>>> Thanks a lot,
>>>
>>> Fernando
>>> _______________________________________________
>>> LLVM Developers mailing list
>>> LLVMdev at cs.uiuc.edu http://llvm.cs.uiuc.edu
>>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>>
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