is. This is most useful to change the CPU submodel. For example,
if configure guesses your machine as `i586-pc-linux-gnu' but you
want to compile a library optimized for 386es, give
- `--host=i386-pc-linux-gnu' or just `--host=i386-linux'. (A
- library compiled for a Pentium (`i586') will still work on a 386,
- but it may be slower.)
+ `--host=i386-pc-linux-gnu' or just `--host=i386-linux' and add the
+ appropriate compiler flags (`-mcpu=i386' will do the trick) to
+ CFLAGS. (A library compiled for a Pentium (`i586') will still work
+ on a 386, but it may be slower.)
If you give just `--build', configure will get confused.
Each case of `iX86' can be `i386', `i486', `i586', or `i686'. All
of those configurations produce a library that can run on any of these
-processors. The library will be optimized for the specified processor,
-but will not use instructions not available on all of them. If you
-want the library to use instructions only available on newer
-processors, give GCC the appropriate `-m' switches via CFLAGS.
+processors if the compiler is configured correctly. The GCC compiler
+by default generates code that's optimized for the machine it's
+configured for and will use the instructions available on that machine.
+For example if your GCC is configured for `i686', gcc will optimize
+for `i686' and might issue some `i686' specific instructions. To
+generate code for other models you should give GCC the appropriate
+`-march=' and `-mcpu=' compiler switches via CFLAGS.
Specific advice for Linux systems
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