[Bug ada/51483] New: [4.7 regression] Ada's cstand.adb:Register_Float_Type makes invalid assumptions about FP representation

["mikpe at it dot uu.se" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51483

             Bug #: 51483
           Summary: [4.7 regression] Ada's cstand.adb:Register_Float_Type
                    makes invalid assumptions about FP representation
    Classification: Unclassified
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: ada
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: mikpe@it.uu.se


Redirected from PR48835:

Attempting to build an Ada-enabled gcc-4.7 cross to m68k-linux fails with:

/tmp/objdir/./gcc/xgcc -B/tmp/objdir/./gcc/
-B/home/mikpe/pkgs/linux-x86/cross-m68k/m68k-unknown-linux/bin/
-B/home/mikpe/pkgs/linux-x86/cross-m68k/m68k-unknown-linux/lib/ -isystem
/home/mikpe/pkgs/linux-x86/cross-m68k/m68k-unknown-linux/include -isystem
/home/mikpe/pkgs/linux-x86/cross-m68k/m68k-unknown-linux/sys-include    -c -g
-O2   -W -Wall -gnatpg -nostdinc   a-assert.adb -o a-assert.o
+===========================GNAT BUG DETECTED==============================+
| 4.7.0 20111203 (experimental) (m68k-unknown-linux) GCC error:            |
| in fp_size_to_prec, at ada/gcc-interface/misc.c:781                      |

(you don't need the m68k-linux Ada support patch for this, vanilla upstream gcc
sources suffice)

This worked up to r177136, but broke due to r177137+177141.

Eric Botcazou commented:
> No, but the new code (cstand.adb:Register_Float_Type) makes an invalid
> assumption about the size of a FP mode given its precision and alignment,
> instead of using the proper interface.  enumerate_modes should probably pass
> GET_MODE_BITSIZE to its callback.  I'd suggest opening a new regression PR for
> this problem.