Whole program optimization and debug symbols

[Ulrich Eckhardt]

Hi!

We're currently looking for a Heisenbug here and one facet we're looking at
is the two features from the topic. Our setup is an MS Windows CE 6,
running on an x86 board. Our code is tompiled using VS2005. A few questions
came up:

1. There is a setting in the "General" tab that says "Whole Program
Optimization". There also is one in the C++ with the same name. Further,
there is one in the linker settings that reads "Link Time Code Generation".
If the one in the C++ tab is set, you get a warning unless you activate the
one for the linker, too. What are the further relations between those
three?

2. We have activated the program database for debugging, which increased the
size of our binary by ~30%. I was under the impression that all additional
info is put into the PDB-file. What additional info is put into the
executable? Also, does this affect optimizations in any way?

Thanks for clarifications!

Uli

[Igor Tandetnik]

Post by Ulrich Eckhardt
1. There is a setting in the "General" tab that says "Whole Program
Optimization". There also is one in the C++ with the same name. Further,
there is one in the linker settings that reads "Link Time Code Generation".
If the one in the C++ tab is set, you get a warning unless you activate the
one for the linker, too. What are the further relations between those
three?

Whole program optimization requires cooperation between compiler and linker. Very roughly, the compiler dumps a parse tree into the object file rather than the actual machine code. At link time, the linker calls back into the compiler to generate machine code; at this point, the compiler can see the whole program, not just a single translation unit - hence the name.

For this to work, compiler and linker settings have to be set in compatible ways. The property on General tab sets them both correctly. You can also change them independently on C/C++ | Optimization and Linker | Optimization tabs, but then it's your responsibility to have them match (if they don't, you may get a warning).