[Ada] Stop mapping Pure on Ada functions to GCC const

[Olivier Hainque <hainque at adacore dot com>]

Hello,

Pure functions in Ada might raise and this doesn't match (any more)
"const" functions in the middle-end, currently assumed to be
SIDE_EFFECTS free, so ...

2008-08-01  Olivier Hainque  <hainque@adacore.com>

	ada/	
	* decl.c (gnat_to_gnu_entity) <case E_Function>: Do not turn Ada
	Pure into GCC const, now implicitely implying nothrow as well.

	testsuite/
	* gnat.dg/raise_from_pure.ad[bs],
	* gnat.dg/wrap_raise_from_pure.ad[bs]: Support for ...
	* gnat.dg/test_raise_from_pure.adb: New test.
	
Otherwise, miscompilation of P at -O2 on at least x86_64-linux in the
testcase below, not emitting the call to Raise_CE_if_0:

    with Raise_From_Pure; use Raise_From_Pure;
    procedure P is
       K : Integer;
    begin
       K := Raise_CE_If_0 (0);
    end;

    package raise_from_pure is
       pragma Pure;
       function Raise_CE_If_0 (P : Integer) return Integer;
    end;

    package body raise_from_pure is
       function Raise_CE_If_0 (P : Integer) return Integer is
       begin
	  if P = 0 then
	     raise Constraint_error;
	  end if;
	  return 1;
       end;
    end;


Bootstrapped and regression tested on x86_64-suse-linux.

Olivier

Attachment: pure-noconst.dif
Description: Text document