llvm dev - Jun 2006 - [LLVMdev] single exit BB

Hello.  I'm new to LLVM, so I apologize if this is a basic question.

I've used llvm-gcc to produce an LLVM assembly file (-S) as well as
the bytecode file.  I then used 'analyze -print-cfg' on the bytecode
and realized that some optimizations have been applied against the
corresponding assembly file.  If I understand the operations, the
emitted assembly file has no optimizations, and hence functions
always start with a single exit BB.

My question is, how can I disable the optimizations (during assembly
and link phases) such that the bytecode file will be the same as the
assembly file?  In particular, if I can preserve the function's single
exit BB, that would be nice.  Thanks!

-- 
Jerry Hom

> I've used llvm-gcc to produce an LLVM assembly file (-S) as well as
> the bytecode file.  I then used 'analyze -print-cfg' on the
bytecode
> and realized that some optimizations have been applied against the
> corresponding assembly file.  If I understand the operations, the
> emitted assembly file has no optimizations, and hence functions
> always start with a single exit BB.
>
> My question is, how can I disable the optimizations (during assembly
> and link phases) such that the bytecode file will be the same as the
> assembly file?  In particular, if I can preserve the function's single
> exit BB, that would be nice.  Thanks!
I think what you want is this:
http://llvm.org/docs/FAQ.html#cfe

"How can I disable all optimizations when compiling code using the LLVM 
GCC front end?

Passing "-Wa,-disable-opt -Wl,-disable-opt" will disable *all* cleanup
and
optimizations done at the llvm level, leaving you with the truly horrible 
code that you desire."

If that doesn't solve your problem let me know.

There is also some good documentation on llvmgcc:
http://llvm.org/docs/CommandGuide/html/llvmgcc.html

-Tanya