llvm dev - Dec 2011 - [LLVMdev] Issues in converting C++ code to C using llvm and llc

Hello All,

I came to know from a friend that using LLVM insfrastucture one can convert
C++ programs to C. I needed this for my cross-compiler because we don't
have support for C++ compilation in our cross-compiler.

I tried following:
http://llvm.org/docs/FAQ.html#translatecxx

While I can generate .bc its llc which gives error. Then I also tried
"clang" as oppose to llvm-g++.

Here is what I want to accomplish: I have a simple c++ prog which I want to
convert to c using llvm
-----------------------------------------------------------------

For example
-------------------------------------------------------------------------
c++ orig file: test_orig.cpp
-----
#include<iostream>
int main()
{
  std::cout << "hello world from C++\n";
  return 0;
}
---------------------------------
c orig file: test_orig.c
-----
#include<stdio>
int main()
{
  printf("Hello workd from C\n");
  return 0;
}
-------------------------------------
I used following commands

% clang -c -emit-llvm test_orig.*EXT* -o test_orig.bc
or
% llvm-g++ -c -emit-llvm test_orig.*EXT* -o test_orig.bc


% llc -march=c test_orig.bc -o test_new.c

and then I simply used gcc to compile test_new.c
gcc test_new.c

When *EXT* is .c then everything works fine however when it is .cpp then
when I try to recompile the test_new.c using gcc it says undefiend
references to std::cout, std::basic_ostream, std::ios_base

I thought that llvm should be able to convert "cout" to
"printf" or
equivalent.
Also how does llvm handles the libraries which are not part of std C but
are in C++.
-----------------------------------------

When I tried to compile my original benchmarks (They are from PARSEC suite)
I see this error

LLVM_ERROR: code generator does not support intrinsic function
"llvm.umul.with.overflow.i32"

How can I avoid this. I am running things on 64-bit Intel machine loaded
with CentOS 5.x

Any help/pointers to solve the above issues would be highly appriciated.

Thanks,
-Raj
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Hi Raj,
> I came to know from a friend that using LLVM insfrastucture one can convert
C++
> programs to C. I needed this for my cross-compiler because we don't
have support
> for C++ compilation in our cross-compiler.
as described in the release notes, the C backend is deprecated and in any case
doesn't work properly.

Ciao, Duncan.
>
> I tried following:
> http://llvm.org/docs/FAQ.html#translatecxx
>
> While I can generate .bc its llc which gives error. Then I also tried
"clang" as
> oppose to llvm-g++.
>
> Here is what I want to accomplish: I have a simple c++ prog which I want to
> convert to c using llvm
> -----------------------------------------------------------------
>
> For example
> -------------------------------------------------------------------------
> c++ orig file: test_orig.cpp
> -----
> #include<iostream>
> int main()
> {
>    std::cout << "hello world from C++\n";
>    return 0;
> }
> ---------------------------------
> c orig file: test_orig.c
> -----
> #include<stdio>
> int main()
> {
>    printf("Hello workd from C\n");
>    return 0;
> }
> -------------------------------------
> I used following commands
>
> % clang -c -emit-llvm test_orig./*EXT*/ -o test_orig.bc
> or
> % llvm-g++ -c -emit-llvm test_orig./*EXT*/ -o test_orig.bc
>
>
> % llc -march=c test_orig.bc -o test_new.c
>
> and then I simply used gcc to compile test_new.c
> gcc test_new.c
>
> When /*EXT*/ is .c then everything works fine however when it is .cpp then
when
> I try to recompile the test_new.c using gcc it says undefiend references to
> std::cout, std::basic_ostream, std::ios_base
>
> I thought that llvm should be able to convert "cout" to
"printf" or equivalent.
> Also how does llvm handles the libraries which are not part of std C but
are in C++.
> -----------------------------------------
>
> When I tried to compile my original benchmarks (They are from PARSEC suite)
> I see this error
>
> LLVM_ERROR: code generator does not support intrinsic function
> "llvm.umul.with.overflow.i32"
>
> How can I avoid this. I am running things on 64-bit Intel machine loaded
with
> CentOS 5.x
>
> Any help/pointers to solve the above issues would be highly appriciated.
>
> Thanks,
> -Raj
>
>
>
>
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