[Bug middle-end/66240] RFE: extend -falign-xyz syntax

["law at redhat dot com" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66240

Jeffrey A. Law <law at redhat dot com> changed:

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                 CC|                            |law at redhat dot com

--- Comment #8 from Jeffrey A. Law <law at redhat dot com> ---
In response to c#2 and c#3, you're more likely to get that kind of "ideal"
solution by hacking the linker rather than the compiler or assembler.  The
linker is in an ideal position to make these kinds of decisions.

You can even use the linker to fill in padding at the end of a function with a
nearby teeny-tiny function.  You don't want to do that too aggressively though
because often functions in the same CU often call each other and you can easily
muck up locality if you move a teeny-tiny function too far from its parents or
children in the call graph/chain.

If you want to get really smart, you start collecting data about the call
graph, chains and frequencies, icache and itlb behavior and use that to drive
general code layout to improve icache/itlb behavior as well as smart alignments
of functions.  Been there, done that :-)