RFA: Add a builtin define for when the floating point registers arenot available

[Nick Clifton <nickc at redhat dot com>]

Hi Aldy, Hi Geoff, Hi Dave,

  I have another powerpc patch for your consideration.
  
  This one adds the definition of a C preprocessor builtin called
  __NO_FPRS__ if the floating point registers are not available.  This
  is the default for the powerpc-eabispe port and can be triggered in
  other powerpc ports via the use of the -msoft-float or the
  -mfloat-gprs=no gcc command line switches.

  The reason that this is important is in building glibc.  In
  glibc/sysdeps/powerpc/fpu/fenv_libc.h there are two macro
  definitions:

    #define fegetenv_register() \
        ({ fenv_t env; asm volatile ("mffs %0" : "=f" (env)); env; })

    #define fesetenv_register(env) \
        ({ double d = (env); asm volatile ("mtfsf 0xff,%0" : : "f" (d)); })

  These definitions only work if the "f" register type is valid, which
  means that both TARGET_HARD_FLOAT and TARGET_FPRS have to be true.
  Thus attempting to build glibc using a powerpc-linux-gnuspe
  toolchain results in the error message:

    error: impossible constraint in 'asm'

  The patch below is part of a fix for this problem.  It provides for
  the definition of __NO_FPRS__ when the floating point registers are
  not available, and with such a definition I could modify the macro
  definitions to be, for example:

    #if defined __NO_FPRS__
    #define fegetenv_register() \
        ({ fenv_t env; asm volatile ("mffs %0" : "=r" (env)); env; })
    #else
    #define fegetenv_register() \
        ({ fenv_t env; asm volatile ("mffs %0" : "=f" (env)); env; })
    #endif

  So - may I apply this patch please ?

  Tested by building a powerpc-linux-gnu toolchain and a
  powerpc-linux-gnuspe toolchain using a three stage gcc/glibc/kernel
  build script.

Cheers
  Nick

gcc/ChangeLog
2005-05-19  Nick Clifton  <nickc@redhat.com>

	* config/rs6000/eabi.h (TARGET_OS_CPP_BUILTINS): Define
	__NO_FPRS__ if the 'f' register type is not available.

Index: eabi.h
===================================================================
RCS file: /cvs/cvsfiles/gnupro/gcc/config/rs6000/eabi.h,v
retrieving revision 1.4
retrieving revision 1.5
diff -c -3 -p -r1.4 -r1.5
*** eabi.h      8 Feb 2005 17:34:57 -0000       1.4
--- eabi.h      19 May 2005 09:37:34 -0000      1.5
***************
*** 41,46 ****
--- 41,48 ----
        builtin_assert ("cpu=powerpc");     \
        builtin_assert ("machine=powerpc"); \
        TARGET_OS_SYSV_CPP_BUILTINS ();     \
+       if (TARGET_SOFT_FLOAT || !TARGET_FPRS) \
+         builtin_define ("__NO_FPRS__");   \
      }                                     \
    while (0)