[llvm-commits] PATCH: BasicBlock metadata

[Ralf Karrenberg]

On 5/8/12 11:40 AM, Richard Osborne wrote:
> On 08/05/12 09:22, Ralf Karrenberg wrote:
>> Hi,
>>
>> please find attached a patch that adds metadata functionality to BasicBlocks.
>> It should include all that is required for full support via BitcodeReader/Writer, AsmParser/Writer, etc.
>>
>> Essentially, the patch mimics behaviour of metadata that is attached to instructions.
>>
>> The chosen syntax for block metadata is as follows:
>>
>> entry:
>>      %property1 !0, %property2 !1
>>    %x = fadd float %a, %b
>>    ret float %x
>>
>> Looking forward to getting feedback on the patch:).
> Some general comments - why do you need special handling / caching of 
> debug loc metadata? Unless the format of debug information is changed 
> debug metadata will only be added to instructions and so this code is 
> unnecessary. You should add some testcases to cover the new 
> functionality and modify the language ref to include a description of 
> basic block metadata. Finally the indentation is incorrect in a number 
> of places. Please use 2 spaces for indentation and avoid tabs.
That's right, LOC metadata is not required - I will remove that.
Testcases / LangRef / indentation - will do and resubmit.
>> Cheers,
>> Ralf
>>     /// hasAddressTaken - returns true if there are any uses of this basic block
>>     /// other than direct branches, switches, etc. to it.
>> -  bool hasAddressTaken() const { return getSubclassDataFromValue() != 0; }
>> +  bool hasAddressTaken() const {
>> +    return (getSubclassDataFromValue()&  ~HasMetadataBit) != 0;
>> +  }
> I think this will result in basic block metadata effecting 
> optimizations. What would happen if you just ignored metadata here?
It will always treat a block that has metadata attached as a block whose 
address has been taken, which results in a crash at a later point (don't 
remember exactly where) because the address was never taken.

Thanks,
Ralf
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