https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106912
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Assignee|rguenth at gcc dot gnu.org |unassigned at gcc dot
gnu.org
Status|ASSIGNED |NEW
--- Comment #7 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to Jakub Jelinek from comment #6)
> Sure, the FUNCTION_TYPE can be shared, so shouldn't be overwritten in place,
> but can be copied with TREE_READONLY cleared on the copy.
> So, if we for whatever reason need to clear const flag on some functions,
> after clearing TREE_READONLY on the node->decl we'd also need to update the
> TREE_TYPE to a version without TREE_READONLY set (so that say if new calls
> are created they don't get wrong fntype) and then walk all call edges to
> that function, updating gimple_call_fntype to the updated type if it was
> equal to the old TREE_TYPE, or to a copy with TREE_READONLY cleared if it
> has TREE_READONLY set on the FUNCTION/METHOD_TYPE).
That will not catch indirect calls to the function. So whatever we do
this part of the problem will remain (the out-of-sync profile). Like
inline int __attribute__((const))
foo (int i)
{
if (i == 0)
return 2;
return 1;
}
int (* __attribute__((const)) bar) () = foo;
int main()
{
int r = 0;
for (int i = 0; i < 10000; ++i)
{
r += foo (r);
r += bar (r);
}
return r;
}
which, when compiled with -O2 -fno-early-inlining -fprofile-arcs results
in the edge counters from the inline copy via foo to be store-motion'ed
but the indirect call clobbering them each iteration.
Using -fprofile-use prevents this because we get an indirect call profiler
call which clobbers all memory, confusing LIM, doing early inlining will
early inline the function before profile instrumentation.
I cannot see how we can fix this without some global flag to ignore
const/pure-ness of functions or alternatively dropping DECL_NONALIASED.
Trying to support surgical un-setting of pure/const for single functions
isn't going to work. Simply disabling IPA inlining for instrumented
builds might also work.
