llvm dev - Aug 2020 - Who uses blocklen_32 in ENTER_SUBBLOCK

Hi,

https://llvm.org/docs/BitCodeFormat.html#enter-subblock-encoding
"The blocklen value is a 32-bit aligned value that specifies the size of
the subblock in 32-bit words. This value allows the reader to skip over the
entire block in one jump."

In the code base, the parsing function of BitstreamCursor::EnterSubBlock
<https://llvm.org/doxygen/BitstreamReader_8h_source.html#l00498> has an
optional argument to return blocklen. The code
<https://llvm.org/doxygen/BitcodeAnalyzer_8cpp_source.html#I00759> at
BitcodeAnalyzer is the only one that uses this argument. But it simply
prints its value. I did not find any code that uses the value to skip
reading bitcode files.

Does anyone know if any clients use blocklen?
<https://llvm.org/doxygen/BitstreamReader_8h_source.html#l00498>
I am interested in this because Bitcode Writer cannot flush memory because
it needs to backfill
<https://llvm.org/doxygen/BitstreamWriter_8h_source.html#l00242> until the
end of a block. At the very-top level, there is such a block
<https://llvm.org/doxygen/BitcodeWriter_8cpp_source.html#I04328>:
MODULE_BLOCK. So the entire bitcode contents cannot be flushed.

Thank you,
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nvm. ValueSymbolTable uses this blocklen a lot.

On Wed, Aug 26, 2020 at 8:35 PM Stephan Z <stephan.yichao.zhao at
gmail.com>
wrote:
> Hi,
>
> https://llvm.org/docs/BitCodeFormat.html#enter-subblock-encoding
> "The blocklen value is a 32-bit aligned value that specifies the size
of
> the subblock in 32-bit words. This value allows the reader to skip over the
> entire block in one jump."
>
> In the code base, the parsing function of BitstreamCursor::EnterSubBlock
> <https://llvm.org/doxygen/BitstreamReader_8h_source.html#l00498> has
an
> optional argument to return blocklen. The code
> <https://llvm.org/doxygen/BitcodeAnalyzer_8cpp_source.html#I00759> at
> BitcodeAnalyzer is the only one that uses this argument. But it simply
> prints its value. I did not find any code that uses the value to skip
> reading bitcode files.
>
> Does anyone know if any clients use blocklen?
> <https://llvm.org/doxygen/BitstreamReader_8h_source.html#l00498>
> I am interested in this because Bitcode Writer cannot flush memory because
> it needs to backfill
> <https://llvm.org/doxygen/BitstreamWriter_8h_source.html#l00242>
until
> the end of a block. At the very-top level, there is such a block
> <https://llvm.org/doxygen/BitcodeWriter_8cpp_source.html#I04328>:
> MODULE_BLOCK. So the entire bitcode contents cannot be flushed.
>
> Thank you,
>
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