[PATCH] ipa: Fix throw in multi-versioned functions [PR106627]

[Richard Biener]

On Wed, Aug 31, 2022 at 11:00 PM Simon Rainer <gcc.gnu@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.gnu@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
>