[LLVMdev] Remove identical or redundant basic blocks?

[John Criswell]

Eugene Toder wrote:
> Would it make sense to have a similar pass that operates on llvm main IR?
>   

The unify exit return node (-mergereturn?) pass should take care of the 
first example.  The -simplifycfg option might take care of the second 
example.  Both work on LLVM IR.

-- John T.
> On Sat, May 8, 2010 at 5:15 PM, Dale Johannesen <dalej at apple.com> wrote:
>   
>> The branch folding pass does this, but it operates later, on the
>> target-dependent form in llc.
>>
>> On May 8, 2010, at 8:48 AM, Heinz Riener wrote:
>>
>>     
>>> Dear all,
>>>
>>> after optimizing a small LLVM example program (i.e., with opt -O3),
>>> the
>>> resulting code contains several basic blocks, which I consider
>>> identical
>>> or redundant.  For instance,
>>>
>>> return:                                           ; preds = %min.exit
>>>   ret i32 0
>>>
>>> bb15:                                             ; preds = %min.exit
>>>   ret i32 0
>>>
>>> or,
>>>
>>> bb7.i:                                            ; preds = %bb1.i
>>>   br label %bb3.i
>>>
>>> bb9.i:                                            ; preds = %bb1.i
>>>   br label %bb3.i
>>>
>>> I think it is safe to remove the blocks bb7.i, bb9.i, bb15 while
>>> replacing each jump to bb15 with return and jumps to bb7.i, bb9.i with
>>> bb3.i.
>>>
>>> Is there any opt pass I can apply to the code to merge or remove these
>>> blocks?
>>>
>>> Heinz
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>>>       
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