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.
(Meta-response: I tried sending the following via nabble.com approx. 40
hours ago and it seems not to have gotten through. Apologies if this
eventually shows up as a duplicate.)
Sorry to question this, but my experience has been otherwise. 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".
The above was part of my semi-successful attempt to solve the following
problem:
1) I'm compiling ARM code for an embedded microcontroller with very
limited memory
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?
