Debugging optimizer problems

[jacob navia]

Hi

I am confronted with a classical problem: a program gives correct 
results when compiled with optimizations off, and gives the wrong ones 
with optimization (-O2) on.

I have isolated the probem in a single file but now there is no way that 
I can further track down the problem to one of the many functions in 
that file.

I have in my small C compiler introduced the following construct:

#pragma optimize(on/off,push/pop)

to deal with optimizer bugs.

#pragma optimize(off)

turns OFF all optimizations until a #pragma optimize(on) is seen or 
until the end of the compiulation unit. If

#pragma optimize(off,push)

is given, the optimization state can be retrieved with a

#pragma optimize(pop), or

#pragma optimize(on)

This has three advantages:

1) Allows the user to reduce the code area where the problem is hiding.

2) Provides a work around to the user for any optimizer bug.

3) Allows gcc developers to find bugs in a more direct fashion.

These pragmas can only be given at a global scope, not within a function.

I do not know gcc internals, and this improvement could be difficult to 
implement, and I do not know either your priorities in gcc development 
but it surely would help users. Obviously I think that the problem is in 
the code I am compiling, not in gcc, but it *could* be in gcc. That 
construct would help enormously.

Thanks in advance for your time.

jacob