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Subject: [Bug tree-optimization/54965] [4.6 Regression] sorry, unimplemented: inlining failed in call to 'foo': function not considered for inlining
Date: Thu, 18 Oct 2012 10:48:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54965

--- Comment #3 from Siarhei Siamashka <siarhei.siamashka at gmail dot com> 2012-10-18 10:47:51 UTC ---
(In reply to comment #2)
> void combine_conjoint_xor_ca_float ()
> {
>     combine_channel_t j = pd_combine_conjoint_xor, k = pd_combine_conjoint_xor;
>     a[0] = k (0, b, 0, a[0]);
>     a[0] = k (0, b, 0, a[0]);
>     a[0] = k (0, b, 0, a[0]);
>     a[0] = j (0, c[0], 0, a[0]);
>     a[0] = k (0, c[0], 0, a[0]);
>     a[0] = k (0, c[0], 0, a[0]);
>     a[0] = k (0, c[0], 0, a[0]);
> 
> you are using indirect function calls here, GCC in 4.6 is not smart enough
> to transform them to direct calls before inlining.  Inlining of
> always-inline indirect function calls is not going to work reliably.

Does this only apply to GCC 4.6?

> Don't use always-inline or don't use indirect function calls to always-inline
> functions.

This looks like it might be really inconvenient. Pixman relies on this
functionality in a number of places by doing something like this:

void always_inline per_pixel_operation_a(...)
{
    ...
}

void always_inline per_pixel_operation_b(...)
{
    ...
}

void always_inline big_function_template(..., per_pixel_operation_ptr foo)
{
    ...
    /* do some calls to foo() in an inner loop */
    ...
}

void big_function_a(...)
{
    big_function_template(..., per_pixel_operation_a);
}

void big_function_b(...)
{
    big_function_template(..., per_pixel_operation_b);
}

Needless to say that we want to be absolutely sure that per-pixel operations
are always inlined. Otherwise the performance gets really bad if the compiler
ever makes a bad inlining decision.

The same functionality can be probably achieved by replacing always_inline
functions with macros. But the code becomes less readable, more error prone and
somewhat more difficult to maintain.