Sriram Natarajan wrote:
> Hi
> Our SFW build process uses this "-xregs=no%appl" while building on
> sparc/sparcv9. Where can I find more information on this compiler flag ?
> What does it do ? I am noticing subtle difference in behavior within an
> application when compiled with -xO4 -xregs=no%appl compared to just
> compiling with -xO4.
>
> - Sriram
Start with the cc manpage:
The -xregs values are for specific -xarch values:
[no%]appl (SPARC)
[Does not] Allow the compiler to generate code
using the application registers as scratch
registers. The application registers are:
g2, g3, g4 (on 32-bit platforms)
g2, g3 (on 64-bit platforms)
It is strongly recommended that all system
software and libraries be compiled using
-xregs=no%appl. System software (including
shared libraries) must preserve these regis-
ters' values for the application. Their use is
intended to be controlled by the compilation
system and must be consistent throughout the
application.
In the SPARC ABI, these registers are
described as application registers. Using
these registers can increase performance
because fewer load and store instructions are
needed. However, such use can conflict with
some old library programs written in assembly
code.
- Ali
