Re: Crosspost: Help wanted from comp.compilers

[tmoran@acm.org]

>The complaint was that some Ada systems recompiled dependents when a file
>was compiled, even if the source code had not changed.
  Consider:
-- file testgo1.ads
package testgo1 is
  i : integer := integer'last-1;
  j : integer := i+2;
end testgo1;
-- file testgo2.ads
with testgo1;
package testgo2 is
  k : integer := testgo1.j;
  function f return integer;
end testgo2;
-- file testgo2.adb
package body testgo2 is
  function f return integer is
  begin return 3;end f;
end testgo2;
-- file testgo.adb
with testgo2;
procedure testgo is
  x : integer;
begin
  x := testgo2.f;
end testgo;

If compiled with "gnatmake -gnato testgo"
the line in testgo1.ads
  j : integer := i+2;
results in a constraint error.  If compiled "gnatmake testgo" it doesn't.
  The procedure testgo can be recompiled with and without -gnato and
it doesn't change the behavior compiled into testgo1.ads  But 'touch'
testgo1.ads to update it's file modification date while changing nothing
at all in the source code, and the next time you say "gnatmake testgo"
or "gnatmake -gnato testgo", it will recompile testgo1.ads and generate
code that does (-gnato) or does not (no -gnato) raise a constraint error.
  That's an example of a case where a textually unchanged spec file
needs to be recompiled because of a change in compiler options.  Other
compilers might lay out records differently according to compiler
switches telling them to optimize for space/time.  That would
require cascading recompiles where the only change is to compiler
optimization switches, not to any source files.