[Info-vax] x86-64 VMS executable image sizes and memory requirements ?

[John Reagan]

On Sunday, December 22, 2019 at 3:25:47 PM UTC-5, Michael Moroney wrote:
> already5chosen at yahoo.com writes:
> 
> >Few numbers for clang/LLVM on x86-64 (not VMS, of course)
> 
> >Option .text size
> >-O0 75456
> >-Oz 45772
> >-Os 44992
> >-O1 56836
> >-O2 45220
> >-O3 46084
> 
> For someone unfamiliar with clang & LLVM, what are the meanings of these
> optimization options?  And will they be available on VMS?

The kinds of optimizations and how they apply to each target is very subject.  For example, here's a description of the gcc options and the underlying optimizations.  Some of which don't exist in GEM (didn't make sense or we just didn't do it) or don't exist in LLVM (for the same reasons)

https://gcc.gnu.org/onlinedocs/gcc/Optimize-Options.html


Since we already have an existing /OPTIMIZE qualifier, we'll do our best to map the traditional GEM settings to clang/LLVM.  Easy ones are /OPT=LEVEL=0 thru 4 are the same as -O0 thru -O4.  We don't have /OPT=SIZE or /OPT=SPEED but have some of that with the /OPT=INLINE=SIZE and /OPT=INLINE=SPEED.  And adding /DEBUG along with /OPT might get you the same as -Og (which is also the same as -O1 on some, but not all platforms.  

As you can see, it is all very subjective and we'll give it a good try.

Beyond that, we do intend to give some access to the full set of clang options (over 500 last time I looked) with an "untested, your mileage may vary and not all features may work properly"