On Wed, Mar 18, 2020 at 10:44:09AM -0700, mark_at_yahoo via Gcc-help wrote: > On 3/16/20 4:34 PM, Segher Boessenkool wrote: > >You can enable the *flags*, sure, but with -O0 those flags do not do > >anything. Exactly as the text above says? The "even if" part. > Sorry to question this, but my experience has been otherwise. >From the manual again: Most optimizations are completely disabled at '-O0' or if an '-O' level is not set on the command line, even if individual optimization flags are specified. Similarly, '-Og' suppresses many optimization passes. > I haven't > tried it in a while (probably last did on an older release) but at least > with gcc-arm, doing: > > -O0 \ > -fbranch-count-reg \ > -fcombine-stack-adjustments \ > -fcompare-elim \ > -fcprop-registers \ > <long list of other flags deleted> > > *did* do something different than just "-O0". It might be interesting to see which compiler flag(s) you see any differences with. > 2) My code includes header files with literally thousands (no > exaggeration) of "static const int ..."s > 3) The code (intentionally) uses only a handful of the consts > 4) If compiled "-O1", no memory is allocated for the thousands of consts > (not even the few that are used) > 5) If compiled "-O0" memory is allocated for each const -- far more > memory than is available > 6) "-O0" executables are much easier to debug at the machine instruction > level (sometimes necessary on microcontrollers) > > Can anyone suggest a minimal set of "-f<options>"s to add to -O0 which > will do what I want, i.e. no code optimizations, but also no memory > allocated for the consts? Try -Og instead? It is mostly like -O1, but almost all debugging should work fine with it (as the option name itself suggests :-) ) Segher
