https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100724
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
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CC| |hubicka at gcc dot gnu.org
--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> ---
-fwhole-program means the program is entirely confined within a single TU,
using
modules might break this in subtle ways. -fwhole-program is really sth
"legacy" meant to help with LTO and the case where no linker plugin is
available. When a linker plugin is available just -flto is as powerful and
using -fwhole-program will only result in subtly to debug issues if you "lied"
to GCC.
I can reproduce the -fwhole-program issue with GCC 10 as well and this likely
means the Fortran FE creates invalid GENERIC and thus two distinct 'twice'
function declarations.
With -flto the WPA stage will unify those, "fixing" the issue (basically
treating the single TU as two distinct TUs which they appearantly are).
When I -fdump-ipa-cgraph-details I indeed see:
twice_/10 (twice) @0x7ffff69cdca8
Type: function
Visibility: external public
References:
Referring:
Function flags:
Called by: MAIN__/1
Calls:
twice_/0 (twice) @0x7ffff69cd000
Type: function definition analyzed
Visibility: public
Aux: @0x7ffff69cd2d0
References:
Referring:
Function flags: body
Called by:
Calls:
so there's an external 'twice' called by main and a distinct, unused,
definition 'twice'. With -fwhole-program you tell GCC that there are
no external users and thus the definition gets promoted 'static' and
is eliminated as unused (GCC doesn't consider it resolving the call
to the external 'twice' which we might consider a bug - but we expect
the frontends to resolve those internal bindings).
