[LLVMdev] [LLVMDev] Has anyone written this?

Jeff Kunkel
Thu, 07 Oct 2010 00:09:02 -0000

I forgot to CC the forum.

I found what was happening. The BranchFolder documentation says:
 // Note that this pass must be run after register allocation, it cannot handle
 // SSA form.

> On Wed, Oct 6, 2010 at 8:05 PM, Jeff Kunkel <jdkunk3 at gmail.com>
wrote:
>> No, I just noticed that blocks were separated.
>>
>>
>> On Wed, Oct 6, 2010 at 8:04 PM, Bob Wilson <bob.wilson at
apple.com> wrote:
>>> I thought that the BranchFolder pass already handled that.  Did you
check?
>>>
>>> On Oct 6, 2010, at 5:03 PM, Jeff Kunkel wrote:
>>>
>>>> It would go something like like the code below. The goal would
be to
>>>> turn the basic blocks which the graph looks like
"...->x->y->..."
>>>> where the instructions of x and y could live in the same basic
block
>>>> without a jump or fall through in between.
>>>>
>>>>    bool runOnMachineFunction(MachineFunction &mf) {
>>>>      BitVector seen( mf.size() );
>>>>      for( unsigned i = 0, e = mf.size(); i != e; ++i ) {
>>>>        if( seen[i] )
>>>>          continue;
>>>>        seen[i] = true;
>>>>        MachineBasicBlock * start, *block;
>>>>        start = block = mf.getBlockNumbered(i);
>>>>        std::vector< MachineBasicBlock* > blocks;
>>>>        while( block->succ_size() == 1 &&
>>>> (*block->succ_begin())->pred_size() == 1 ) {
>>>>          block = *block->succ_begin();
>>>>          seen[block->getNumber()] = true;
>>>>          blocks.push_back( block );
>>>>        }
>>>>        // TODO:
>>>>        // For each basic block bb in blocks in order of
insersion:
>>>>        // 1. Remove basic blocks in the block vector from the
machine function.
>>>>        // 2. Remove the jump from the start block if it exists.
>>>>        // 3. Add the instruction from bb into the start block.
>>>>      }
>>>>
>>>> Thanks,
>>>> Jeff Kunkel
>>>>
>>>> On Wed, Oct 6, 2010 at 7:49 PM, Bob Wilson <bob.wilson at
apple.com> wrote:
>>>>>
>>>>> On Oct 6, 2010, at 4:31 PM, Jeff Kunkel wrote:
>>>>>
>>>>>> Has anyone written a pass at the MachineFunction level
which combines
>>>>>> machine basic blocks which is guaranteed to be the
single predecessor
>>>>>> to another block? Or is there a reason not to combine
them?
>>>>>
>>>>> I'm not sure exactly what transformation you're
referring to, but BranchFolder::OptimizeBranches does a lot of things like that.
>>>
>>>
>>
>