Re: [PATCH] X86: Provide a CTOR for stringop_algs [PR100246].

[Iain Sandoe <iain@sandoe.co.uk>]

> On 5 Jul 2021, at 14:23, Richard Biener <richard.guenther@gmail.com> wrote:
> 
> On Mon, Jul 5, 2021 at 3:04 PM Iain Sandoe <iain@sandoe.co.uk> wrote:
>> 
>> Hi Richard,
>> 
>>> On 5 Jul 2021, at 11:50, Richard Biener via Gcc-patches <gcc-patches@gcc.gnu.org> wrote:
>>> 
>>> On Sun, Jul 4, 2021 at 10:04 PM Iain Sandoe <iain@sandoe.co.uk> wrote:
>> 
>>>> Several older compilers fail to build modern GCC because of missing
>>>> or incomplete C++11 support.
>>>> 
>>>> (although the PR mentions clang, specifically, this has also been reported
>>>> for some GCC versions within the range that should be able to bootstrap
>>>> GCC)
>>>> 
>>>> There are several possible solutions proposed in the PR, this one seems
>>>> the least invasive.
>>>> 
>>>> The header is pulled into the gcov code that builds with C, so we have to
>>>> make the CTOR conditional on C++.
>>>> 
>>>> tested on Darwin12 with xcode-6, bootstrapped on x86_64-darwin and linux.
>>>> OK for master / GCC-11?
>>> 
>>> Hmm, what is specifically built with a C compiler?  gcov.c not, I think.
>> 
>> any C compilation that includes tm.h
>> 
>> well, libgcc2 fails too on a quick check here -  but ISTR there was something in
>> libgcov and I checked with Martin that it was intentionally compiled with C compiler.
>> 
>>> Instead of commenting the CTOR, does it work to comment the whole stringop_algs
>>> type?
>> 
>> I don’t think that will work because it’s in a header that’s transitively included by tm.h
>> which is then included loads of places.
>> 
>>> Also it seems on trunk this CTOR is no more?
>> 
>> The addition of the CTOR is the fix for the C++ compile fail in the PR, the conditional is
>> only there because the same header is compiled by C and C++.
> 
> Whoops sorry - I was confused.  The patch looks OK to me if you add a comment
> before the CTOR why it was added (maybe quoting the error that happens)

Thanks, pushed as below.
Iain

-------

X86: Provide a CTOR for stringop_algs [PR100246].

Several older compilers fail to build modern GCC because of missing
or incomplete C++11 support.

Signed-off-by: Iain Sandoe <iain@sandoe.co.uk>

PR bootstrap/100246 - [11/12 Regression] GCC will not bootstrap with clang 3.4/3.5 [xcode 5/6, Darwin 12/13]

	PR bootstrap/100246

gcc/ChangeLog:

	* config/i386/i386.h (struct stringop_algs): Define a CTOR for
	this type.
---
 gcc/config/i386/i386.h | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/gcc/config/i386/i386.h b/gcc/config/i386/i386.h
index 6e0340a4b60..03d176143fe 100644
--- a/gcc/config/i386/i386.h
+++ b/gcc/config/i386/i386.h
@@ -73,6 +73,15 @@ struct stringop_algs
 {
   const enum stringop_alg unknown_size;
   const struct stringop_strategy {
+    /* Several older compilers delete the default constructor because of the
+       const entries (see PR100246).  Manually specifying a CTOR works around
+       this issue.  Since this header is used by code compiled with the C
+       compiler we must guard the addition.  */
+#ifdef __cplusplus
+    stringop_strategy(int _max = -1, enum stringop_alg _alg = libcall,
+		      int _noalign = false)
+      : max (_max), alg (_alg), noalign (_noalign) {}
+#endif
     const int max;
     const enum stringop_alg alg;
     int noalign;
-- 
2.24.1