On Tue, Feb 7, 2012 at 1:26 PM, Konstantin Vladimirov <konstantin.vladimi...@gmail.com> wrote: > Hi, > > Consider some project, consisting of files: a.c, b.c, d.c and e.c > > Compiler is gcc 4.6.2 > > Files a.c and b.c are performance bottlenecks and requires heavy > cross-module inline, so must be compiled with -flto option > Files d.c and e.c is preffered to be compiled with lto option too, but > they are of special usage, and requires some registers (say r9 and > r10) to be fixed (with -ffixed-<reg> option) during compilation. > > All these files forms single binary. > > Now the problem is: if I compiling > > gcc $OPTIONS -flto a.c -o a.o > gcc $OPTIONS -flto b.c -o b.o > gcc $OPTIONS -ffixed-r9 -ffixed-r10 -flto d.c -o d.o > gcc $OPTIONS -ffixed-r9 -ffixed-r10 -flto e.c -o d.o > > and then > > gcc $OPTIONS -flto a.o b.o d.o e.o -o a.out > > Then registers inside d.o and e.o are being reallocated at link time, > and r9, r10 are used in the d.o and e.o parts in the resulted binary. > Also I can not specify fixed regs to final link, because this will fix > registers in a.o and b.o parts, that will affect performance. > > The best way for me seems to somehow separately link pseudo-object > files a.o and b.o with -flto to simple object (say x.o), and then link > e.o and d.o to single, say, y.o, and then call linker to finally link > binary without cross-module optimizations. But I can not find > possibility to do it, and I doubt if this at all conforms with lto > ideology.
That's indeed the way to go, but you don't need anything fancy like partial linking. gcc $OPTIONS -flto a.c -o a.o gcc $OPTIONS -flto b.c -o b.o gcc $OPTIONS -ffixed-r9 -ffixed-r10 d.c -o d.o gcc $OPTIONS -ffixed-r9 -ffixed-r10 e.c -o e.o gcc $OPTIONS -flto a.o b.o d.o e.o should do it automatically. Just make sure to not compile d.o and e.o with -flto. Richard. > So, I want to perform link-time optimizations between a.o and b.o, and > don't want them between (a.o or b.o) and (d.o or e.o) > > How can I approach this? > > Thanks in advance for everyone, who will help. > > --- > With best regards, Konstantin
