Compiler Option: -arch

Set target architecture for improved/restricted code generation or cross-compiling

-arch < architecture >

The target architecture. Recognized values:

  • Related to 32bit x86:
    • 386
    • 486 (default for x86)
    • 586
    • 686
    • athlon
    • athlon-xp
    • athlon-fx
    • k8-sse3
    • pentium-mmx
    • pentium2
    • pentium3
    • pentium4
    • pentium4-sse3
  • Related to 64bit x86_64:
    • x86_64, x86-64, amd64
  • Related to 32bit ARM:
    • armv6
    • armv7-a (default for ARM)
  • Related to 64bit ARM (AArch64):
    • aarch64
  • Others:
    • native: For compiling to the architecture which the compiler is running on.
    • 32, 64: For quick cross-compiling to the 32bit or 64bit version of the default architecture.

The -arch compiler option sets the target CPU architecture. This can be used for multiple purposes:
  • Improving code generation; for example: You can use -arch 686 to override the default -arch 486, and the compiler will generate faster code in some cases, by using certain instructions which were not available on i486 (or other CPUs older than i686).
  • Restricting code generation; for example: You can use -arch 386 to limit the compiler to using only i386-compatible instructions.
  • Cross-compiling; for example: You can use -arch x86_64 on 32bit x86 systems to cross-compile to 64bit x86_64.

The exact impact which the -arch setting has on code generation depends on the code generation backend that is being used. The x86 ASM backend (-gen gas) handles the -arch setting and adjusts code generation accordingly in some cases. When using the GCC backend (-gen gcc), the specified architecture will be passed on to gcc via gcc -march=<...>, causing gcc to generate code for the specified architecture.

However, -arch only affects newly generated code, but not pre-compiled code such as the FreeBASIC runtime libraries, or any other library from the lib/ directory. For example, using -arch 386 is not necessarily enough to get a pure i386 executable -- it also depends on how all the libraries that will be linked in were compiled.

The -arch 32 and -arch 64 shortcuts are similar to gcc's -m32/-m64 options. On 32bit architectures, -arch 64 is an abbreviation for cross-compiling to the default 64bit version of the architecture (e.g. from 32bit x86 to 64bit x86_64, or 32bit ARM to 64bit AArch64), and -arch 32 does nothing. On 64bit systems, it is the other way round: -arch 32 cross-compiles to the default 32bit architecture, while -arch 64 does nothing.

The -arch native shortcut is similar to gcc's -march=native option. On x86, it causes fbc to try and detect the host CPU automatically based on the cpuid instruction and its availability or results. On other architectures, this will currently simply use the architecture which the compiler itself was built for. Under -gen gcc this will use gcc -march=native.

Specifying an -arch setting incompatible to the native architecture will trigger cross-compilation, just like the -target option, except that only the target architecture, but not the target operating system, is changed.

See also:
Back to Compiler Options
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