Target processor detection

["Piotr Wyderski" <piotr dot wyderski at microgen dot pl>]

I am working on a portable low-level library of atomic operations,
so I need to detect the exact type of the target processor, which is
specified by -mcpu or -march. However, there are two problems.
On a sparc-based platform (Sun Fire 880, Solaris 2.8, 4x UltraSparc III)
this program

#if defined(__arch64__)
    #warning 64-bit architecture
#else
    #warning 32-bit architecture
#endif

#if defined(__sparcv9__) || defined(__sparc_v9__) || defined(__sparcv9)
    #warning Sparc V9
#endif

compiled using GCC 3.4.1

    g++ -mcpu=v9 -mv8plus -mvis -m32 main.cpp

displays only

    #warning 32-bit architecture

with

    g++ -mcpu=v9 -mv8plus -mvis -m64 main.cpp

the result is

    #warning 64-bit architecture
    #warning Sparc V9

Why does __sparc_v9__ depend on the number of bits instead of the -mcpu?
Is this a GCC bug? I've found an e-mail by Jakub Jelinek, which claims, that

"__sparc_v9__ macro is for -mcpu=ultrasparc or -mcpu=v9, which is implied
by -m64, but can be used in 32-bit code as well. __sparc_v9__ means
using v9 instructions, __sparc__ __arch64__ means 64-bit ABI with the
exception of Solaris which uses __sparcv9."

It seems that my interpretation is confirmed by the above text and that it
is
a GCC bug. Could you please clarify the exact meaning of __sparc_v9__?

The second problem is more general. Is it possible to change the meaning
of __i386, __sparc, etc. in the next release of GCC? It should return the
number provided by the user in -mcpu, for example:

    -mcpu=i386 => __i386 = 300
    -mcpu=i486 => __i386 = 400
    -mcpu=i586 => __i386 = 500
    -mcpu=pentiumpro => __i386 = 600
    -mcpu=pentium2 => __i386 = 625
    -mcpu=pentium3 => __i386 = 650
    -mcpu=pentium4 => __i386 = 700

    -mcpu=v8 => __sparc = 800
    -mcpu=v8 -mv8plus => __sparc = 850
    -mcpu=v9 => __sparc = 900
    -mcpu=ultrasparc => __sparc = 1000

and so on. Currently it is just defined to "1", which doesn't help much
if the programmer would like to use something very architecture-specific.
This modification would be backward compatible, because the result of

    #if defined(__i386)

is the same as in the current compiler version.

    Best regards
    Piotr Wyderski








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