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Re: [PATCH, C++] Warn on redefinition of builtin functions (PR c++/71973)

From: Jason Merrill <jason at redhat dot com>
To: Bernd Edlinger <bernd dot edlinger at hotmail dot de>, Joseph Myers <joseph at codesourcery dot com>
Cc: "gcc-patches at gcc dot gnu dot org" <gcc-patches at gcc dot gnu dot org>, Jeff Law <law at redhat dot com>
Date: Tue, 1 Nov 2016 11:02:18 -0400
Subject: Re: [PATCH, C++] Warn on redefinition of builtin functions (PR c++/71973)
Authentication-results: sourceware.org; auth=none
References: <HE1PR0701MB2169DB217F73D8111DA9F690E4C70@HE1PR0701MB2169.eurprd07.prod.outlook.com> <AM4PR0701MB21627728F5677776D53257B9E4D10@AM4PR0701MB2162.eurprd07.prod.outlook.com> <alpine.DEB.2.20.1610171802210.24572@digraph.polyomino.org.uk> <AM4PR0701MB21623781CE7CE49B190E86F0E4D00@AM4PR0701MB2162.eurprd07.prod.outlook.com>

On 10/17/2016 03:18 PM, Bernd Edlinger wrote:

Regarding this hunk:

        /* Whether or not the builtin can throw exceptions has no
          bearing on this declarator.  */
-      TREE_NOTHROW (olddecl) = 0;
+      TREE_NOTHROW (olddecl) = TREE_NOTHROW (newdecl);

You may ask, why the old code was working most of the time.
I think, usually, when types_match == true, there happens another
assignment to TREE_NOTHROW, later in that function around line 2183:

       /* Merge the type qualifiers.  */
       if (TREE_READONLY (newdecl))
         TREE_READONLY (olddecl) = 1;
       if (TREE_THIS_VOLATILE (newdecl))
         TREE_THIS_VOLATILE (olddecl) = 1;
       if (TREE_NOTHROW (newdecl))
         TREE_NOTHROW (olddecl) = 1;

This is in a big "if (types_match)", so I think that explains,
why the old code did work normally, and why it fails if the
parameter don't match, but I still have no idea what to say
in the comment, except that the code should exactly do what
the comment above says.

I think a better fix would be to add a copy of TREE_NOTHROW to the elseblock of the if (types_match), to go with the existing copies ofTREE_READONLY and TREE_THIS_VOLATILE. But yes, duplicate_decls is a mess.


Jason

Follow-Ups:
- Re: [PATCH, C++] Warn on redefinition of builtin functions (PR c++/71973)
  - From: Bernd Edlinger

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