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From: "egallager at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug target/34422] Bootstrap error with --enable-fixed-point
 (configure should reject --enable-fixed-point on platforms that don't support
 it)
Date: Wed, 25 May 2022 02:15:30 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D34422

--- Comment #10 from Eric Gallager <egallager at gcc dot gnu.org> ---
Current code is like this:

# Enable C extension for fixed-point arithmetic.
AC_ARG_ENABLE(fixed-point,
[AS_HELP_STRING([--enable-fixed-point],
                [enable fixed-point arithmetic extension to C])],
[],
[
  case $target in
    arm*)
      enable_fixed_point=3Dyes
      ;;

    mips*-*-*)
      enable_fixed_point=3Dyes
      ;;
    loongarch*-*-*)
      enable_fixed_point=3Dyes
      ;;
    *)
      AC_MSG_WARN([fixed-point is not supported for this target, ignored])
      enable_fixed_point=3Dno
      ;;
  esac
])
AC_SUBST(enable_fixed_point)

Let's check the documentation for AC_ARG_ENABLE:
https://www.gnu.org/savannah-checkouts/gnu/autoconf/manual/autoconf-2.71/ht=
ml_node/Package-Options.html

So, argument 3 is used if the flag is given, and argument 4 is used when the
flag is *not* given... so when it says "ignored" in the warning, there's
nothing being ignored, because the flag wasn't actually given... perhaps the
3rd and 4th arguments just need to be swapped?=