[llvm-dev] [EXTERNAL] Re: Backend emitting to string instead of file

[Frank Winter via llvm-dev]

Yes, the destructor hint was golden.

Frank


On 4/14/20 10:27 PM, Craig Topper wrote:
> I think buffer_ostream has an internal buffer that doesn't flush until 
> its destructor runs. What happens
> if you just pass "stream" instead of pstream?
>
> ~Craig
>
>
> On Tue, Apr 14, 2020 at 7:08 PM Frank Winter via llvm-dev 
> <llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>> wrote:
>
>     I can use llc to compile my IR module to amdgcn with some non-zero
>     output. However, if try to write the output (assembly or object) to a
>     string (via buffer_ostream) the resulting string has always zero
>     length.
>     Here the code changes I do:
>
>     Original llc:
>
>            if (Target->addPassesToEmitFile(PM, *OS,
>                                            DwoOut ? &DwoOut->os() :
>     nullptr,
>                                            FileType, NoVerify, MMIWP))
>
>
>     Now, with this tiny change I was hoping to write to a string
>     instead of
>     the output stream defined by the command line parameters:
>
>     std::string outStr;
>     raw_string_ostream stream(outStr);
>     buffer_ostream pstream(stream);
>     if (Target->addPassesToEmitFile(PM, pstream,
>                                          DwoOut ? &DwoOut->os() : nullptr,
>                                          FileType, NoVerify, MMIWP))
>
>
>     later, e.g., after PM.run(*M), I check the string for content with
>
>     WithColor::warning(errs(), argv[0]) << "with flush, output size: " <<
>     outStr.length() << "\n";
>
>
>     But this always yields "with flush, output size: 0"
>
>     I tried to flush the raw_string_ostream before using the string, same
>     result.
>
>     The used command line was
>
>     llc -march=amdgcn -mcpu=gfx906 < module.ll
>
>
>     Anyone see what's wrong with the code?
>
>
>     Frank
>
>
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