Overriding optimization for individual portions of C code

Is it possible with gcc to specify that a portion of code should be compiled without any optimizations, overriding the -O option given in the command line? The solution consisting of isolating that portion of code, and placing it in a separate file is not what I am looking for.

Problem running optimized IA64 code that invokes hand-coded assembly language function

I have a function F written in IA64 assembly language function. This function is invoked from a C program P. If I compile P with gcc (version 3.2.3) under Linux, and with no optimization options, the resulting executable runs flawlessly. If I compile P with -O then the resulting executable fails.