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MIPS: Implement __multi3 for GCC7 MIPS64r6 builds

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GCC7 is a bit too eager to generate suboptimal __multi3 calls (128bit
multiply with 128bit result) for MIPS64r6 builds, even in code which
doesn't explicitly use 128bit types, such as the following:

unsigned long func(unsigned long a, unsigned long b)
{
	return a > (~0UL) / b;
}

Which GCC rearanges to:

return (unsigned __int128)a * (unsigned __int128)b > 0xffffffffffffffff;

Therefore implement __multi3, but only for MIPS64r6 with GCC7 as under
normal circumstances we wouldn't expect any calls to __multi3 to be
generated from kernel code.

Reported-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: James Hogan <jhogan@kernel.org>
Tested-by: Waldemar Brodkorb <wbx@openadk.org>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Maciej W. Rozycki <macro@mips.com>
Cc: Matthew Fortune <matthew.fortune@mips.com>
Cc: Florian Fainelli <florian@openwrt.org>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/17890/
This commit is contained in:
James Hogan 2017-12-07 07:20:46 +00:00 • committed by Ralf Baechle
parent ccf85c7442
commit ebabcf17bc
3 changed files with 73 additions and 1 deletions
Download patch file Download diff file Expand all files Collapse all files

17
arch/mips/lib/libgcc.h
View file

@ -10,10 +10,18 @@ typedef int word_type __attribute__ ((mode (__word__)));
struct DWstruct {
int high, low;
};
struct TWstruct {
long long high, low;
};
#elif defined(__LITTLE_ENDIAN)
struct DWstruct {
int low, high;
};
struct TWstruct {
long long low, high;
};
#else
#error I feel sick.
#endif
@ -23,4 +31,13 @@ typedef union {
long long ll;
} DWunion;
#if defined(CONFIG_64BIT) && defined(CONFIG_CPU_MIPSR6)
typedef int ti_type __attribute__((mode(TI)));
typedef union {
struct TWstruct s;
ti_type ti;
} TWunion;
#endif
#endif /* __ASM_LIBGCC_H */