[LLVMdev] Transition C->bitcode->assembly->object looses frame pointers

[Alexander Potapenko]

Hi everyone,

We're doing some compile-time instrumentation according to the following scheme:

  llvm-gcc -O1 -g $in -emit-llvm -S -o $name.ll
  opt  -O2 -load Instr.so $INSTR_FLAGS $name.ll -S -o $name-inst.ll
  llc  $name-inst.ll -o $name.S
  g++ -c $name.S

However it turns out that the code instrumented this way is missing
frame pointers (e.g. backtrace() and/or libunwind cannot unwind the
stack when necessary).
Moreover, removing the instrumentation doesn't help: a simple
transition to and from bitcode doesn't help:

  llvm-gcc -O1 -g $in -emit-llvm -S -o $name.ll
  llc  $name.ll -o $name.S
  g++ -c $name.S

We also tried to use Clang and to add -fno-omit-frame-pointers and
--disable-fp-elim -- do not work either.

On the other hand, compiling the code in a single pass of
gcc/llvm-gcc/clang does preserve the frame pointers.

Does anyone happen to know where the problem might be? Are there any
other flags we're missing?

Thanks,
Alexander Potapenko