llvm dev - Apr 2020 - Backend emitting to string instead of file

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

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> 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
>
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
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When passing in "stream" instead I get

error: non-const lvalue reference to type 'llvm::raw_pwrite_stream' 
cannot bind to a value of unrelated type 'llvm::raw_string_ostream'

I am not sure what else to try.

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
>
>
>     _______________________________________________
>     LLVM Developers mailing list
>     llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>
>     https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>    
<https://urldefense.proofpoint.com/v2/url?u=https-3A__lists.llvm.org_cgi-2Dbin_mailman_listinfo_llvm-2Ddev&d=DwMFaQ&c=CJqEzB1piLOyyvZjb8YUQw&r=tFpAzszScTWMAFcrGFW5xg&m=oviBDHJqEC2vv35g8O4RBcGJEiOrougT5L0aM0gH3Dg&s=KDhhMM6rb9PhZnhzJYUujXsFibjWX29VxkIGd3ln_iY&e=>
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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
>
>
>     _______________________________________________
>     LLVM Developers mailing list
>     llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>
>     https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>    
<https://urldefense.proofpoint.com/v2/url?u=https-3A__lists.llvm.org_cgi-2Dbin_mailman_listinfo_llvm-2Ddev&d=DwMFaQ&c=CJqEzB1piLOyyvZjb8YUQw&r=tFpAzszScTWMAFcrGFW5xg&m=oviBDHJqEC2vv35g8O4RBcGJEiOrougT5L0aM0gH3Dg&s=KDhhMM6rb9PhZnhzJYUujXsFibjWX29VxkIGd3ln_iY&e=>
>
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