CONFIG_ARCH_SUPPORTS_INT128: Why not mips, s390, powerpc, and alpha?

[George Spelvin]

I've been tracking down when "umulditi3" support was added to various
gcc platforms.  So far, I've found:

ia64: 2005-07-28, gcc 4.1.0
https://gcc.gnu.org/viewcvs/gcc?view=revision&revision=102463

mips: 2008-06-09, gcc 4.4.0
https://gcc.gnu.org/viewcvs/gcc?view=revision&revision=136600 

alpha: 2013-02-01, gcc 4.8.0
https://gcc.gnu.org/viewcvs/gcc?view=revision&revision=195668

s390: 2011-10-07, gcc 4.7.0
https://gcc.gnu.org/viewcvs/gcc?view=revision&revision=179647

ppc64: 2013-02-01, gcc 4.8.0
https://gcc.gnu.org/viewcvs/gcc?view=revision&revision=195667


Here's a revised s390 patch.

>From e8ea8c0a5d618385049248649b8c13717b598a42 Mon Sep 17 00:00:00 2001
From: George Spelvin <lkml at sdf.org>
Date: Sat, 30 Mar 2019 10:27:14 +0000
Subject: [PATCH v2] s390: Enable CONFIG_ARCH_SUPPORTS_INT128 on 64-bit builds

If a platform supports a 64x64->128-bit widening multiply,
that allows more efficient scaling of 64-bit values in various
parts of the kernel.  GCC advertises __int128 support with the
__INT128__ #define, but we care about efficient inline
support, so this is a separate flag.

For s390, that was added on 2011-10-07 by
https://gcc.gnu.org/viewcvs/gcc?view=revision&revision=179647
which is part of GCC 4.7.

Signed-off-by: George Spelvin <lkml at sdf.org>
---
 arch/s390/Kconfig | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
index ed554b09eb3f..6ddaee6573f4 100644
--- a/arch/s390/Kconfig
+++ b/arch/s390/Kconfig
@@ -372,6 +372,7 @@ endchoice
 
 config 64BIT
 	def_bool y
+	select ARCH_SUPPORTS_INT128 if GCC_VERSION >= 40700 || CC_IS_CLANG
 
 config COMPAT
 	def_bool y
-- 
2.20.1