[Bug fortran/45318] New: Do more parenthesis simplification with -fno-protect-parens

[Bug fortran/45318] New: Do more parenthesis simplification with -fno-protect-parens

[burnus at gcc dot gnu dot org]

Fortran preserves () in expressions - in many cases, it shouldn't need to do so
if 
-fno-protect-parens is specified. The option currently affects only the middle
end, but there might be some cases where it is preserved without needing to be.
(Though, I might be wrong and everything is already properly simplified).

Note: The out most parenthesis can not always be removed without changing the
semantics, e.g.

  call copy ( (a), a)
contains
  subroutine copy (x, y)
    intent(in) :: x
    intent(out) :: y
is valid but only works if the "(a)" [-> temporary] is not optimized to "a".

In some cases, one might need to check for the unsave_math_optimization flag
before changing, e.g., "2+(a-2)" to "a" - or rather "(a)".


-- 
           Summary: Do more parenthesis simplification with -fno-protect-
                    parens
           Product: gcc
           Version: 4.6.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: enhancement
          Priority: P3
         Component: fortran
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: burnus at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45318

[Bug fortran/45318] Do more parenthesis simplification with -fno-protect-parens

[rguenth at gcc dot gnu dot org]

------- Comment #1 from rguenth at gcc dot gnu dot org  2010-08-18 14:23 -------
(In reply to comment #0)
> In some cases, one might need to check for the unsave_math_optimization flag
> before changing, e.g., "2+(a-2)" to "a" - or rather "(a)".

The whole point of PAREN_EXPR in the middle-end is to avoid transforming
2 + (a - 2) even _with_ -funsafe-math-optimizations / -ffast-math!


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45318

[Bug fortran/45318] Do more parenthesis simplification with -fno-protect-parens

[burnus at gcc dot gnu dot org]

------- Comment #2 from burnus at gcc dot gnu dot org  2010-08-18 17:44 -------
(In reply to comment #1)
> (In reply to comment #0)
> > In some cases, one might need to check for the unsave_math_optimization flag
> > before changing, e.g., "2+(a-2)" to "a" - or rather "(a)".
> 
> The whole point of PAREN_EXPR in the middle-end is to avoid transforming
> 2 + (a - 2) even _with_ -funsafe-math-optimizations / -ffast-math!

Well, I am talking about FE optimizations with -fno-protect-parens (note the
"no-"). The PAREN_EXPR protection *is* and *should* one done with
-fprotect-parens (which is the default setting).

In terms of the middle end, -fno-protect-parens and -fprotect-parens are both
properly handled.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45318