[llvm-dev] Who uses blocklen_32 in ENTER_SUBBLOCK

Stephan Z via llvm-dev llvm-dev at lists.llvm.org
Wed Aug 26 22:11:45 PDT 2020

nvm. ValueSymbolTable uses this blocklen a lot.

On Wed, Aug 26, 2020 at 8:35 PM Stephan Z <stephan.yichao.zhao at gmail.com>

> 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,
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20200826/fd8a01f7/attachment.html>

More information about the llvm-dev mailing list