Getting debug information w/ optimizations

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1

I am trying to build a bytecode file with optimizations and debug
information using llvm-gcc. Compiling with "-g" works fine, but when
I add the optimizations flag, all debug information disappears.

On the other hand, if I first "-emit-llvm" with "-g" and no
optimizations, and then apply "opt -std-compile-opts", then debug
information seems to be preserved.

I have two questions:
1) The "Source Level Debugging with LLVM" documentation page states
the following: "Compiling a program with "-O3 -g" gives you full
debug information that is always available and accurate for reading
[...]" Is this incorrect or am I missing something? What is causing
the debug info to be wiped?
2) Are the llvm-gcc -O levels (e.g. -O1, -O2, etc.) approximately
equivalent to the regular gcc -O levels, or are they really quite
different? I couldn't find any recent discussion on this in the
archives.

Many thanks,
Marc

2

Hi, running llvm-gcc with optimization turns off debug info. That
is because the LLVM optimizers do not yet know how to deal with it
well.

1) The "Source Level Debugging with LLVM" documentation page states
the following: "Compiling a program with "-O3 -g" gives you full
debug information that is always available and accurate for reading
[...]" Is this incorrect or am I missing something? What is causing
the debug info to be wiped?

It is not being generated in the first place. The above quote reflects
a vision of the future and not present reality!

2) Are the llvm-gcc -O levels (e.g. -O1, -O2, etc.) approximately
equivalent to the regular gcc -O levels, or are they really quite
different? I couldn't find any recent discussion on this in the
archives.

In my experience -O2 is about the same, while gcc's -O3 and llvm-gcc's
-O3 differ quite a lot. Your mileage may vary :slight_smile:

Ciao,

Duncan.