Using the GNU Compiler Collection (GCC): Basic PowerPC Built-in Functions Available on all Configurations

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#### 6.60.22.1 Basic PowerPC Built-in Functions Available on all Configurations

Built-in Function: void __builtin_cpu_init (void)

  This function is a `nop` on the PowerPC platform and is included solely to maintain API compatibility with the x86 builtins.

Built-in Function: int __builtin_cpu_is (const char *cpuname)

  This function returns a value of `1` if the run-time CPU is of type cpuname and returns `0` otherwise

  The `__builtin_cpu_is` function requires GLIBC 2.23 or newer which exports the hardware capability bits. GCC defines the macro `__BUILTIN_CPU_SUPPORTS__` if the `__builtin_cpu_supports` built-in function is fully supported.

  If GCC was configured to use a GLIBC before 2.23, the built-in function `__builtin_cpu_is` always returns a 0 and the compiler issues a warning.

  The following CPU names can be detected:

  ‘`power10`’

    IBM POWER10 Server CPU.

  ‘`power9`’

    IBM POWER9 Server CPU.

  ‘`power8`’

    IBM POWER8 Server CPU.

  ‘`power7`’

    IBM POWER7 Server CPU.

  ‘`power6x`’

    IBM POWER6 Server CPU (RAW mode).

  ‘`power6`’

    IBM POWER6 Server CPU (Architected mode).

  ‘`power5+`’

    IBM POWER5+ Server CPU.

  ‘`power5`’

    IBM POWER5 Server CPU.

  ‘`ppc970`’

    IBM 970 Server CPU (ie, Apple G5).

  ‘`power4`’

    IBM POWER4 Server CPU.

  ‘`ppca2`’

    IBM A2 64-bit Embedded CPU

  ‘`ppc476`’

    IBM PowerPC 476FP 32-bit Embedded CPU.

  ‘`ppc464`’

    IBM PowerPC 464 32-bit Embedded CPU.

  ‘`ppc440`’

    PowerPC 440 32-bit Embedded CPU.

  ‘`ppc405`’

    PowerPC 405 32-bit Embedded CPU.

  ‘`ppc-cell-be`’

    IBM PowerPC Cell Broadband Engine Architecture CPU.

  Here is an example:

      #ifdef __BUILTIN_CPU_SUPPORTS__
        if (__builtin_cpu_is ("power8"))
          {
             do_power8 (); // POWER8 specific implementation.
          }
        else
      #endif
          {
             do_generic (); // Generic implementation.
          }

Built-in Function: int __builtin_cpu_supports (const char *feature)

  This function returns a value of `1` if the run-time CPU supports the HWCAP feature feature and returns `0` otherwise.

  The `__builtin_cpu_supports` function requires GLIBC 2.23 or newer which exports the hardware capability bits. GCC defines the macro `__BUILTIN_CPU_SUPPORTS__` if the `__builtin_cpu_supports` built-in function is fully supported.

  If GCC was configured to use a GLIBC before 2.23, the built-in function `__builtin_cpu_supports` always returns a 0 and the compiler issues a warning.

  The following features can be detected:

  ‘`4xxmac`’

    4xx CPU has a Multiply Accumulator.

  ‘`altivec`’

    CPU has a SIMD/Vector Unit.

  ‘`arch_2_05`’

    CPU supports ISA 2.05 (eg, POWER6)

  ‘`arch_2_06`’

    CPU supports ISA 2.06 (eg, POWER7)

  ‘`arch_2_07`’

    CPU supports ISA 2.07 (eg, POWER8)

  ‘`arch_3_00`’

    CPU supports ISA 3.0 (eg, POWER9)

  ‘`arch_3_1`’

    CPU supports ISA 3.1 (eg, POWER10)

  ‘`archpmu`’

    CPU supports the set of compatible performance monitoring events.

  ‘`booke`’

    CPU supports the Embedded ISA category.

  ‘`cellbe`’

    CPU has a CELL broadband engine.

  ‘`darn`’

    CPU supports the `darn` (deliver a random number) instruction.

  ‘`dfp`’

    CPU has a decimal floating point unit.

  ‘`dscr`’

    CPU supports the data stream control register.

  ‘`ebb`’

    CPU supports event base branching.

  ‘`efpdouble`’

    CPU has a SPE double precision floating point unit.

  ‘`efpsingle`’

    CPU has a SPE single precision floating point unit.

  ‘`fpu`’

    CPU has a floating point unit.

  ‘`htm`’

    CPU has hardware transaction memory instructions.

  ‘`htm-nosc`’

    Kernel aborts hardware transactions when a syscall is made.

  ‘`htm-no-suspend`’

    CPU supports hardware transaction memory but does not support the `tsuspend.` instruction.

  ‘`ic_snoop`’

    CPU supports icache snooping capabilities.

  ‘`ieee128`’

    CPU supports 128-bit IEEE binary floating point instructions.

  ‘`isel`’

    CPU supports the integer select instruction.

  ‘`mma`’

    CPU supports the matrix-multiply assist instructions.

  ‘`mmu`’

    CPU has a memory management unit.

  ‘`notb`’

    CPU does not have a timebase (eg, 601 and 403gx).

  ‘`pa6t`’

    CPU supports the PA Semi 6T CORE ISA.

  ‘`power4`’

    CPU supports ISA 2.00 (eg, POWER4)

  ‘`power5`’

    CPU supports ISA 2.02 (eg, POWER5)

  ‘`power5+`’

    CPU supports ISA 2.03 (eg, POWER5+)

  ‘`power6x`’

    CPU supports ISA 2.05 (eg, POWER6) extended opcodes mffgpr and mftgpr.

  ‘`ppc32`’

    CPU supports 32-bit mode execution.

  ‘`ppc601`’

    CPU supports the old POWER ISA (eg, 601)

  ‘`ppc64`’

    CPU supports 64-bit mode execution.

  ‘`ppcle`’

    CPU supports a little-endian mode that uses address swizzling.

  ‘`scv`’

    Kernel supports system call vectored.

  ‘`smt`’

    CPU support simultaneous multi-threading.

  ‘`spe`’

    CPU has a signal processing extension unit.

  ‘`tar`’

    CPU supports the target address register.

  ‘`true_le`’

    CPU supports true little-endian mode.

  ‘`ucache`’

    CPU has unified I/D cache.

  ‘`vcrypto`’

    CPU supports the vector cryptography instructions.

  ‘`vsx`’

    CPU supports the vector-scalar extension.

  Here is an example:

      #ifdef __BUILTIN_CPU_SUPPORTS__
        if (__builtin_cpu_supports ("fpu"))
          {
             asm("fadd %0,%1,%2" : "=d"(dst) : "d"(src1), "d"(src2));
          }
        else
      #endif
          {
             dst = __fadd (src1, src2); // Software FP addition function.
          }

The following built-in functions are also available on all PowerPC processors:

    uint64_t __builtin_ppc_get_timebase ();
    unsigned long __builtin_ppc_mftb ();
    double __builtin_unpack_ibm128 (__ibm128, int);
    __ibm128 __builtin_pack_ibm128 (double, double);
    double __builtin_mffs (void);
    void __builtin_mtfsf (const int, double);
    void __builtin_mtfsb0 (const int);
    void __builtin_mtfsb1 (const int);
    void __builtin_set_fpscr_rn (int);

The `__builtin_ppc_get_timebase` and `__builtin_ppc_mftb` functions generate instructions to read the Time Base Register. The `__builtin_ppc_get_timebase` function may generate multiple instructions and always returns the 64 bits of the Time Base Register. The `__builtin_ppc_mftb` function always generates one instruction and returns the Time Base Register value as an unsigned long, throwing away the most significant word on 32-bit environments. The `__builtin_mffs` return the value of the FPSCR register. Note, ISA 3.0 supports the `__builtin_mffsl()` which permits software to read the control and non-sticky status bits in the FSPCR without the higher latency associated with accessing the sticky status bits. The `__builtin_mtfsf` takes a constant 8-bit integer field mask and a double precision floating point argument and generates the `mtfsf` (extended mnemonic) instruction to write new values to selected fields of the FPSCR. The `__builtin_mtfsb0` and `__builtin_mtfsb1` take the bit to change as an argument. The valid bit range is between 0 and 31. The builtins map to the `mtfsb0` and `mtfsb1` instructions which take the argument and add 32. Hence these instructions only modify the FPSCR[32:63] bits by changing the specified bit to a zero or one respectively. The `__builtin_set_fpscr_rn` builtin allows changing both of the floating point rounding mode bits. The argument is a 2-bit value. The argument can either be a `const int` or stored in a variable. The builtin uses the ISA 3.0 instruction `mffscrn` if available, otherwise it reads the FPSCR, masks the current rounding mode bits out and OR’s in the new value.

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