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ec8bf18814
It was only GCC 10 that fixed a MIPS64r6 code generation issue with a
`__multi3' libcall inefficiently produced to perform 64-bit widening
multiplication while suitable machine instructions exist to do such a
calculation. The fix went in with GCC commit 48b2123f6336 ("re PR
target/82981 (unnecessary __multi3 call for mips64r6 linux kernel)").
Adjust our code accordingly, removing build failures such as:
mips64-linux-ld: lib/math/div64.o: in function `mul_u64_add_u64_div_u64':
div64.c:(.text+0x84): undefined reference to `__multi3'
with the GCC versions affected.
Fixes: ebabcf17bc ("MIPS: Implement __multi3 for GCC7 MIPS64r6 builds")
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202601140146.hMLODc6v-lkp@intel.com/
Signed-off-by: Maciej W. Rozycki <macro@orcam.me.uk>
Cc: stable@vger.kernel.org # v4.15+
Reviewed-by: David Laight <david.laight.linux@gmail.com.
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
55 lines
1.3 KiB
C
55 lines
1.3 KiB
C
// SPDX-License-Identifier: GPL-2.0
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#include <linux/export.h>
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#include "libgcc.h"
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/*
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* GCC 9 & older can suboptimally generate __multi3 calls for mips64r6, so for
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* that specific case only we implement that intrinsic here.
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*
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* See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82981
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*/
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#if defined(CONFIG_64BIT) && defined(CONFIG_CPU_MIPSR6) && (__GNUC__ < 10)
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/* multiply 64-bit values, low 64-bits returned */
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static inline long long notrace dmulu(long long a, long long b)
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{
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long long res;
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asm ("dmulu %0,%1,%2" : "=r" (res) : "r" (a), "r" (b));
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return res;
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}
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/* multiply 64-bit unsigned values, high 64-bits of 128-bit result returned */
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static inline long long notrace dmuhu(long long a, long long b)
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{
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long long res;
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asm ("dmuhu %0,%1,%2" : "=r" (res) : "r" (a), "r" (b));
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return res;
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}
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/* multiply 128-bit values, low 128-bits returned */
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ti_type notrace __multi3(ti_type a, ti_type b)
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{
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TWunion res, aa, bb;
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aa.ti = a;
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bb.ti = b;
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/*
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* a * b = (a.lo * b.lo)
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* + 2^64 * (a.hi * b.lo + a.lo * b.hi)
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* [+ 2^128 * (a.hi * b.hi)]
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*/
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res.s.low = dmulu(aa.s.low, bb.s.low);
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res.s.high = dmuhu(aa.s.low, bb.s.low);
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res.s.high += dmulu(aa.s.high, bb.s.low);
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res.s.high += dmulu(aa.s.low, bb.s.high);
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return res.ti;
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}
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EXPORT_SYMBOL(__multi3);
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#endif /* 64BIT && CPU_MIPSR6 && GCC9 */
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