[Bug ipa/101279] Function attributes often block inlining

["frankhb1989 at gmail dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101279

frankhb1989 at gmail dot com changed:

           What    |Removed                     |Added
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                 CC|                            |frankhb1989 at gmail dot com

--- Comment #3 from frankhb1989 at gmail dot com ---
There is a more specific instance here: can_inline_edge_by_limits_p in
ipa-inline.cc treats flags and "optimize" attributes differently.

While it is reasonable to reject inlining for semantic mismatch from different
global flags, "opts_for_fn (caller->decl) != opts_for_fn (callee->decl)" looks
quite unnatural. In practice it means missing of valid opportunity of inlining,
unless the programmer knows what should go under the hood and decides to
propagate "always_inline" plus the "optimize" attributes manually in the
declarations of *all* callees (including lambda-expressions in C++),
*recursively*. Adding "__attribute__((flatten))" can be a workaround sometimes,
but it does not always generated desired code, and often too slow.

This is somewhat worse than the case of "-fwrapv" whose semantic is easier to
reason in the generated code.