Andrew Haley - Re: [x86 PATCH] Mark builtin intrinsics as "nothrow" (original) (raw)

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• From: Andrew Haley
• To: Andi Kleen
• Cc: Steven Bosscher , gcc-patches at gcc dot gnu dot org
• Date: Sat, 10 Feb 2007 11:10:06 +0000
• Subject: Re: [x86 PATCH] Mark builtin intrinsics as "nothrow"
• References: 1404.68.35.10.103.1171077243.squirrel@mail.eyesopen.com.suse.lists.egcs-patches 200702101103.07058.steven.bosscher@gmail.com.suse.lists.egcs-patches <p73bqk21dcg.fsf@bingen.suse.de>

Andi Kleen writes:

Steven Bosscher stevenb.gcc@gmail.com writes:

On Saturday 10 February 2007 04:14, Roger Sayle wrote:

The following simple patch tweaks i386.c's builtin_def function to annotate the back-end intrinsics as "nothrow", by setting the TREE_NOTHROW bit of their "decl". This allows for simplification of the CFG at the tree-level for C++ codes, such as in the example below:

Is this really safe if the builtin may trap (e.g. builtins for division vs. division by zero)?

AFAIK OS signals cannot be safely caught by C++ exception handlers.

Sure they can. We've been doing this in libgcj for years.

Divide builtins must not be marked nothrow when compiling with -fnon-call-exceptions.

Andrew.

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