[gcc(refs/users/aoliva/heads/testme)] hardcfr: add optional checkpoints [ada docs]

[Alexandre Oliva]

https://gcc.gnu.org/g:c66ec1a0792b659633ac071693791a87842a0dae

commit c66ec1a0792b659633ac071693791a87842a0dae
Author: Alexandre Oliva <oliva@adacore.com>
Date:   Thu Jun 8 01:34:59 2023 -0300

    hardcfr: add optional checkpoints [ada docs]
    
    Previously, control flow redundancy only checked the visited bitmap
    against the control flow graph at return points and before mandatory
    tail calls, missing various other possibilities of exiting a
    subprogram, such as by raising or propagating exceptions, and calling
    noreturn functions.  The checks inserted before returns also prevented
    potential tail-call optimizations.
    
    This incremental change introduces options to control checking at each
    of these previously-missed checkpoints.  Unless disabled, a cleanup is
    introduced to check when an exceptions escapes a subprogram.  To avoid
    disrupting sibcall optimizations, when they are enabled, checks are
    introduced before calls whose results are immediately returned,
    whether or not they are ultimately optimized.  If enabled, checks are
    introduced before noreturn calls and exception raises, or only before
    nothrow noreturn calls.
    
    Add examples of code transformations to the GNAT RM.
    
    
    for  gcc/ada/ChangeLog
    
            * doc/gnat_rm/security_hardening_features.rst: Document
            optional hardcfr checkpoints.

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