Re: Work around PR65873

[Jan Hubicka <hubicka at ucw dot cz>]

> On Wed, May 13, 2015 at 12:12 AM, Jan Hubicka <hubicka@ucw.cz> wrote:
> >
> > Hi,
> > this patch works around PR where we refuse to inline always_inline memcpy
> > into function with explicit Ofast optimization attribute.  This is because
> > we think we can not promote -fno-fast-math code to -fast-math code.
> > This is of course safe for memcpy because it contains to fast-math code,
> > but we don't really do the analysis for each of the flags we check.
> >
> > Earlier compilers was happily producing wrong code here and it seems practical
> > to do that on GCC 5 to deal with common falout.  I will implement the more
> > fine grained check incrementally.
> >
> > Bootstrapped/regtested x86_64-linux. Will commit it to mainline shortly and
> > to release branch later this week.
> 
> Hmm, the changelog or the description above doesn't cover the
> 
> @@ -481,6 +490,17 @@ can_inline_edge_p (struct cgraph_edge *e
>           e->inline_failed = CIF_OPTIMIZATION_MISMATCH;
>           inlinable = false;
>         }
> +      /* If explicit optimize attribute are not used, the mismatch is caused
> +        by different command line options used to build different units.
> +        Do not care about COMDAT functions - those are intended to be
> +         optimized with the optimization flags of module they are used in.
> +        Also do not care about mixing up size/speed optimization when
> +        DECL_DISREGARD_INLINE_LIMITS is set.  */
> +      else if ((callee->merged
> +               && !lookup_attribute ("optimize",
> +                                     DECL_ATTRIBUTES (caller->decl)))
> +              || DECL_DISREGARD_INLINE_LIMITS (callee->decl))
> +       ;
>        /* If mismatch is caused by merging two LTO units with different
>          optimizationflags we want to be bit nicer.  However never inline
>          if one of functions is not optimized at all.  */
> 
> hunk.

Ah, sorry. The change was intended, but I forgot to write about it.
Yep, as comment says this makes us a bit more relaxed about inlining COMDATs
when the prevailing variant is -Os and caller body is -O3 or vice versa.

Honza
> 
> >         PR ipa/65873
> >         * ipa-inline.c (can_inline_edge_p): Allow early inlining of always
> >         inlines across optimization boundary.
> >         * testsuite/gcc.c-torture/compile/pr65873.c: New testcase.
> > Index: ipa-inline.c
> > ===================================================================
> > --- ipa-inline.c        (revision 223093)
> > +++ ipa-inline.c        (working copy)
> > @@ -427,46 +427,55 @@ can_inline_edge_p (struct cgraph_edge *e
> >               && lookup_attribute ("always_inline",
> >                                    DECL_ATTRIBUTES (callee->decl)));
> >
> > +     /* Until GCC 4.9 we did not check the semantics alterning flags
> > +       bellow and inline across optimization boundry.
> > +       Enabling checks bellow breaks several packages by refusing
> > +       to inline library always_inline functions. See PR65873.
> > +       Disable the check for early inlining for now until better solution
> > +       is found.  */
> > +     if (always_inline && early)
> > +       ;
> >        /* There are some options that change IL semantics which means
> >           we cannot inline in these cases for correctness reason.
> >          Not even for always_inline declared functions.  */
> >        /* Strictly speaking only when the callee contains signed integer
> >           math where overflow is undefined.  */
> > -      if ((check_maybe_up (flag_strict_overflow)
> > -          /* this flag is set by optimize.  Allow inlining across
> > -             optimize boundary.  */
> > -          && (!opt_for_fn (caller->decl, optimize)
> > -              == !opt_for_fn (callee->decl, optimize) || !always_inline))
> > -         || check_match (flag_wrapv)
> > -         || check_match (flag_trapv)
> > -         /* Strictly speaking only when the callee uses FP math.  */
> > -         || check_maybe_up (flag_rounding_math)
> > -         || check_maybe_up (flag_trapping_math)
> > -         || check_maybe_down (flag_unsafe_math_optimizations)
> > -         || check_maybe_down (flag_finite_math_only)
> > -         || check_maybe_up (flag_signaling_nans)
> > -         || check_maybe_down (flag_cx_limited_range)
> > -         || check_maybe_up (flag_signed_zeros)
> > -         || check_maybe_down (flag_associative_math)
> > -         || check_maybe_down (flag_reciprocal_math)
> > -         /* We do not want to make code compiled with exceptions to be brought
> > -            into a non-EH function unless we know that the callee does not
> > -            throw.  This is tracked by DECL_FUNCTION_PERSONALITY.  */
> > -         || (check_match (flag_non_call_exceptions)
> > -             /* TODO: We also may allow bringing !flag_non_call_exceptions
> > -                to flag_non_call_exceptions function, but that may need
> > -                extra work in tree-inline to add the extra EH edges.  */
> > -             && (!opt_for_fn (callee->decl, flag_non_call_exceptions)
> > -                 || DECL_FUNCTION_PERSONALITY (callee->decl)))
> > -         || (check_maybe_up (flag_exceptions)
> > -             && DECL_FUNCTION_PERSONALITY (callee->decl))
> > -         /* Strictly speaking only when the callee contains function
> > -            calls that may end up setting errno.  */
> > -         || check_maybe_up (flag_errno_math)
> > -         /* When devirtualization is diabled for callee, it is not safe
> > -            to inline it as we possibly mangled the type info.
> > -            Allow early inlining of always inlines.  */
> > -         || (!early && check_maybe_down (flag_devirtualize)))
> > +     else if ((check_maybe_up (flag_strict_overflow)
> > +              /* this flag is set by optimize.  Allow inlining across
> > +                 optimize boundary.  */
> > +              && (!opt_for_fn (caller->decl, optimize)
> > +                  == !opt_for_fn (callee->decl, optimize) || !always_inline))
> > +             || check_match (flag_wrapv)
> > +             || check_match (flag_trapv)
> > +             /* Strictly speaking only when the callee uses FP math.  */
> > +             || check_maybe_up (flag_rounding_math)
> > +             || check_maybe_up (flag_trapping_math)
> > +             || check_maybe_down (flag_unsafe_math_optimizations)
> > +             || check_maybe_down (flag_finite_math_only)
> > +             || check_maybe_up (flag_signaling_nans)
> > +             || check_maybe_down (flag_cx_limited_range)
> > +             || check_maybe_up (flag_signed_zeros)
> > +             || check_maybe_down (flag_associative_math)
> > +             || check_maybe_down (flag_reciprocal_math)
> > +             /* We do not want to make code compiled with exceptions to be
> > +                brought into a non-EH function unless we know that the callee
> > +                does not throw.
> > +                This is tracked by DECL_FUNCTION_PERSONALITY.  */
> > +             || (check_match (flag_non_call_exceptions)
> > +                 /* TODO: We also may allow bringing !flag_non_call_exceptions
> > +                    to flag_non_call_exceptions function, but that may need
> > +                    extra work in tree-inline to add the extra EH edges.  */
> > +                 && (!opt_for_fn (callee->decl, flag_non_call_exceptions)
> > +                     || DECL_FUNCTION_PERSONALITY (callee->decl)))
> > +             || (check_maybe_up (flag_exceptions)
> > +                 && DECL_FUNCTION_PERSONALITY (callee->decl))
> > +             /* Strictly speaking only when the callee contains function
> > +                calls that may end up setting errno.  */
> > +             || check_maybe_up (flag_errno_math)
> > +             /* When devirtualization is diabled for callee, it is not safe
> > +                to inline it as we possibly mangled the type info.
> > +                Allow early inlining of always inlines.  */
> > +             || (!early && check_maybe_down (flag_devirtualize)))
> >         {
> >           e->inline_failed = CIF_OPTIMIZATION_MISMATCH;
> >           inlinable = false;
> > @@ -481,6 +490,17 @@ can_inline_edge_p (struct cgraph_edge *e
> >           e->inline_failed = CIF_OPTIMIZATION_MISMATCH;
> >           inlinable = false;
> >         }
> > +      /* If explicit optimize attribute are not used, the mismatch is caused
> > +        by different command line options used to build different units.
> > +        Do not care about COMDAT functions - those are intended to be
> > +         optimized with the optimization flags of module they are used in.
> > +        Also do not care about mixing up size/speed optimization when
> > +        DECL_DISREGARD_INLINE_LIMITS is set.  */
> > +      else if ((callee->merged
> > +               && !lookup_attribute ("optimize",
> > +                                     DECL_ATTRIBUTES (caller->decl)))
> > +              || DECL_DISREGARD_INLINE_LIMITS (callee->decl))
> > +       ;
> >        /* If mismatch is caused by merging two LTO units with different
> >          optimizationflags we want to be bit nicer.  However never inline
> >          if one of functions is not optimized at all.  */
> > Index: testsuite/gcc.c-torture/compile/pr65873.c
> > ===================================================================
> > --- testsuite/gcc.c-torture/compile/pr65873.c   (revision 0)
> > +++ testsuite/gcc.c-torture/compile/pr65873.c   (revision 0)
> > @@ -0,0 +1,14 @@
> > +typedef __SIZE_TYPE__ size_t;
> > +
> > +extern inline __attribute__ ((__always_inline__, __gnu_inline__, __artificial__, __nothrow__, __leaf__)) void *
> > +memcpy (void *__restrict __dest, const void *__restrict __src, size_t __len)
> > +{
> > +  return __builtin___memcpy_chk (__dest, __src, __len, __builtin_object_size (__dest, 0));
> > +}
> > +
> > +__attribute__((optimize ("Ofast"))) void
> > +bar (void *d, void *s, size_t l)
> > +{
> > +  memcpy (d, s, l);
> > +}
> > +