Hi,
Thanks for committing the patch. I created PR106816 to track the noreturn/pure
problem.
Regards
Simon Rainer
On Fri, Sep 2, 2022, at 08:03, Richard Biener wrote:
> On Thu, Sep 1, 2022 at 7:51 PM Simon Rainer <gcc....@vvalter.com> wrote:
> >
> > Hi,
> >
> > Thanks for taking a look at my patch. I tested some combinations with
> > pure/noreturn attributes. gcc seems to ignore those attributes on
> > multiversion functions and generates sub-optimal assembly.
> > But I wasn't able to fix this by simply copying members like DECL_PURE_P.
> > It's pretty hard for me to tell which members of tree are relevant for a
> > function declaration and should be copied and which should not be copied.
> >
> > Anyway, I think the TREE_NOTHROW change is the most important one, because
> > it leads to correctness problems (and is what broke my original program :D
> > ), so could you please commit my patch as I don't have write-access myself.
>
> Sure, will do - thanks for the fix!
>
> >
> > Should I open a new bug on bugzilla for the pure/noreturn issue?
>
> Yes, I think it's worth investigating.
>
> Richard.
>
> > Thanks
> > Simon Rainer
> >
> >
> > On Thu, Sep 1, 2022, at 08:37, Richard Biener wrote:
> > > On Wed, Aug 31, 2022 at 11:00 PM Simon Rainer <gcc....@vvalter.com> wrote:
> > > >
> > > > Hi,
> > > >
> > > > This patch fixes PR106627. I ran the i386.exp tests on my
> > > > x86_64-linux-gnu machine with a fully bootstrapped checkout. I also
> > > > tested manually that no exception handling code is generated if none of
> > > > the function versions throws an exception.
> > > > I don't have access to a machine to test the change to rs6000.cc, but
> > > > the code seems like an exact copy and I don't see a reason why it
> > > > shouldn't work there the same way.
> > > >
> > > > Regards
> > > > Simon Rainer
> > > >
> > > > From 6fcb1c742fa1d61048f7d63243225a8d1931af4a Mon Sep 17 00:00:00 2001
> > > > From: Simon Rainer <gcc....@vvalter.com>
> > > > Date: Wed, 31 Aug 2022 20:56:04 +0200
> > > > Subject: [PATCH] ipa: Fix throw in multi-versioned functions [PR106627]
> > > >
> > > > Any multi-versioned function was implicitly declared as noexcept, which
> > > > leads to an abort if an exception is thrown inside the function.
> > > > The reason for this is that the function declaration is replaced by a
> > > > newly created dispatcher declaration, which has TREE_NOTHROW always set
> > > > to 1. Instead we need to set TREE_NOTHROW to the value of the original
> > > > declaration.
> > >
> > > Looks quite obvious. The middle-end to target interface is a bit iffy
> > > since we have
> > > to duplicate this everywhere. There's also other flags like
> > > pure/const and noreturn
> > > that do not impose correctness issues but may cause irritations if the IL
> > > gets
> > > a call to the dispatcher not marked noreturn but there's no code
> > > following.
> > >
> > > That said, the fix looks good to me.
> > >
> > > Thanks,
> > > Richard.
> > >
> > > > PR ipa/106627
> > > >
> > > > gcc/ChangeLog:
> > > >
> > > > * config/i386/i386-features.cc
> > > > (ix86_get_function_versions_dispatcher): Set TREE_NOTHROW
> > > > correctly for dispatcher declaration
> > > > * config/rs6000/rs6000.cc
> > > > (rs6000_get_function_versions_dispatcher): Likewise
> > > >
> > > > gcc/testsuite/ChangeLog:
> > > >
> > > > * g++.target/i386/pr106627.C: New test.
> > > > ---
> > > > gcc/config/i386/i386-features.cc | 1 +
> > > > gcc/config/rs6000/rs6000.cc | 1 +
> > > > gcc/testsuite/g++.target/i386/pr106627.C | 30 ++++++++++++++++++++++++
> > > > 3 files changed, 32 insertions(+)
> > > > create mode 100644 gcc/testsuite/g++.target/i386/pr106627.C
> > > >
> > > > diff --git a/gcc/config/i386/i386-features.cc
> > > > b/gcc/config/i386/i386-features.cc
> > > > index d6bb66cbe01..5b3b1aeff28 100644
> > > > --- a/gcc/config/i386/i386-features.cc
> > > > +++ b/gcc/config/i386/i386-features.cc
> > > > @@ -3268,6 +3268,7 @@ ix86_get_function_versions_dispatcher (void *decl)
> > > >
> > > > /* Right now, the dispatching is done via ifunc. */
> > > > dispatch_decl = make_dispatcher_decl (default_node->decl);
> > > > + TREE_NOTHROW(dispatch_decl) = TREE_NOTHROW(fn);
> > > >
> > > > dispatcher_node = cgraph_node::get_create (dispatch_decl);
> > > > gcc_assert (dispatcher_node != NULL);
> > > > diff --git a/gcc/config/rs6000/rs6000.cc b/gcc/config/rs6000/rs6000.cc
> > > > index 2f3146e56f8..9280da8a5c8 100644
> > > > --- a/gcc/config/rs6000/rs6000.cc
> > > > +++ b/gcc/config/rs6000/rs6000.cc
> > > > @@ -24861,6 +24861,7 @@ rs6000_get_function_versions_dispatcher (void
> > > > *decl)
> > > >
> > > > /* Right now, the dispatching is done via ifunc. */
> > > > dispatch_decl = make_dispatcher_decl (default_node->decl);
> > > > + TREE_NOTHROW(dispatch_decl) = TREE_NOTHROW(fn);
> > > >
> > > > dispatcher_node = cgraph_node::get_create (dispatch_decl);
> > > > gcc_assert (dispatcher_node != NULL);
> > > > diff --git a/gcc/testsuite/g++.target/i386/pr106627.C
> > > > b/gcc/testsuite/g++.target/i386/pr106627.C
> > > > new file mode 100644
> > > > index 00000000000..a67f5ae4813
> > > > --- /dev/null
> > > > +++ b/gcc/testsuite/g++.target/i386/pr106627.C
> > > > @@ -0,0 +1,30 @@
> > > > +/* PR c++/103012 Exception handling with multiversioned functions */
> > > > +/* { dg-do run } */
> > > > +/* { dg-require-ifunc "" } */
> > > > +
> > > > +#include <assert.h>
> > > > +
> > > > +__attribute__((target("default")))
> > > > +void f() {
> > > > + throw 1;
> > > > +}
> > > > +
> > > > +__attribute__((target("sse4.2,bmi")))
> > > > +void f() {
> > > > + throw 2;
> > > > +}
> > > > +
> > > > +int main()
> > > > +{
> > > > + try {
> > > > + f();
> > > > + }
> > > > + catch(...)
> > > > + {
> > > > + return 0;
> > > > + }
> > > > +
> > > > + assert (false);
> > > > + return 1;
> > > > +}
> > > > +
> > > > --
> > > > 2.34.1
> > > >
> > >
>
