[cfe-commits] Patch to clang -emit-llvm-bc on Linux

[Collin Winter]

Hi Daniel,

On Wed, Apr 29, 2009 at 7:24 PM, Daniel Dunbar <daniel at zuster.org> wrote:
> Hi Colin,
>
> I would definitely like to improve this, but I also think that the llvm-gcc
> behavior (which clang is just copying) was chosen by design. Poor design,
> perhaps, but I believe the intent was that -emit-llvm simply changes the
> output format, not the functionality. Thus -S -emit-llvm is output in LLVM
> IR, -c -emit-llvm is output in LLVM bitcode, -emit-llvm alone is an
> executable, but having been compiled with LLVM tools. The problem, of
> course, is when the linker doesn't have LLVM support.
>
> I'd rather not break "compatibility" with llvm-gcc... is there a specific
> reason you wante to change this (why not use "-c"?). If it just comes down
> to eliminating the current bad user experience, we could augment the tool
> chain to understand whether the system supports LLVM inputs and avoid trying
> to pass them to the linker and give an error instead.

My biggest reason for wanting to change this is that clang
-emit-llvm-bc works as expected on Darwin but works differently on
Linux. This recently broke our project's build: testing the change on
our Darwin laptops worked just fine, but broke our Linux-based
buildslaves. We can certainly use -emit-llvm -c going forward, but the
difference between platforms seems like a bug.

Note that currently in clang, -emit-llvm-bc -c doesn't work:

obj/$ Util/llvm/Debug/bin/clang -ccc-echo -O3 -c -emit-llvm-bc  -I.
-IInclude -I../trunk -I../trunk/Include   -DPy_BUILD_CORE
../trunk/Python/llvm_inline_functions.c -o
Python/llvm_inline_functions.bc
 "/usr/local/google/collinwinter/us/obj/Util/llvm/Debug/bin/clang-cc"
-triple i386-unknown-linux-gnu -S -disable-free -main-file-name
llvm_inline_functions.c --relocation-model static --disable-fp-elim
--unwind-tables=0 --fmath-errno=1 -DPy_BUILD_CORE -I. -IInclude
-I../trunk -I../trunk/Include -O3 -fdiagnostics-show-option -o
/tmp/cc-X0bB5X.s -x c ../trunk/Python/llvm_inline_functions.c
 "/usr/bin/gcc" -O3 -emit-llvm-bc -I. -IInclude -I../trunk
-I../trunk/Include -DPy_BUILD_CORE -c -o
Python/llvm_inline_functions.bc -x assembler /tmp/cc-X0bB5X.s
obj/$ file Python/llvm_inline_functions.bc
Python/llvm_inline_functions.bc: ELF 32-bit LSB relocatable, Intel
80386, version 1 (SYSV), not stripped

clang -emit-llvm -c produces the bitcode as expected, though. I'll
change our build steps to use -emit-llvm -c.

Thanks,
Collin Winter