llvm dev - Feb 2019 - Improving textual IR format for nameless blocks

After watching a few different people get confused about nameless blocks in
llvm IR, and recalling my own confusion a few years ago, I'd like to change
the syntax slightly to make it a bit clearer.

This is similar to the change made for instruction names in
https://llvm.org/PR2480 a decade ago.

Two changes:
1. Change the parsing of a numeric block label to parse as a value number
rather than a string.
2. When printing blocks, always print the value number as a proper label,
except for the initial block.

See proposed change in https://reviews.llvm.org/D58548
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> On 2019 Feb  22, at 07:33, James Y Knight via llvm-dev <llvm-dev at
lists.llvm.org> wrote:
> 
> After watching a few different people get confused about nameless blocks in
llvm IR, and recalling my own confusion a few years ago, I'd like to change
the syntax slightly to make it a bit clearer.
> 
> This is similar to the change made for instruction names in
https://llvm.org/ <https://llvm.org/>PR2480 a decade ago.
> 
> Two changes:
> 1. Change the parsing of a numeric block label to parse as a value number
rather than a string.
> 2. When printing blocks, always print the value number as a proper label,
except for the initial block.
> 
> See proposed change in https://reviews.llvm.org/D58548
<https://reviews.llvm.org/D58548>
I'm in favour of this.  I think it improves readability at low cost.
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Thanks so much for making this happen. I have written many, many clang test
cases with convoluted FileCheck regexes that match "label:" and
";
:<numbered label>" so they pass with and without NDEBUG.

On Fri, Feb 22, 2019 at 7:34 AM James Y Knight via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
> After watching a few different people get confused about nameless blocks
> in llvm IR, and recalling my own confusion a few years ago, I'd like to
> change the syntax slightly to make it a bit clearer.
>
> This is similar to the change made for instruction names in
> https://llvm.org/PR2480 a decade ago.
>
> Two changes:
> 1. Change the parsing of a numeric block label to parse as a value number
> rather than a string.
> 2. When printing blocks, always print the value number as a proper label,
> except for the initial block.
>
> See proposed change in https://reviews.llvm.org/D58548
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
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> On Feb 22, 2019, at 7:33 AM, James Y Knight via llvm-dev <llvm-dev at
lists.llvm.org> wrote:
> 
> After watching a few different people get confused about nameless blocks in
llvm IR, and recalling my own confusion a few years ago, I'd like to change
the syntax slightly to make it a bit clearer.
> 
> This is similar to the change made for instruction names in
https://llvm.org/ <https://llvm.org/>PR2480 a decade ago.
> 
> Two changes:
> 1. Change the parsing of a numeric block label to parse as a value number
rather than a string.
> 2. When printing blocks, always print the value number as a proper label,
except for the initial block.
> 
> See proposed change in https://reviews.llvm.org/D58548
<https://reviews.llvm.org/D58548>
Great idea!

-Chris

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