MIPS: Implement __multi3 for GCC7 MIPS64r6 builds

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 <[email protected]>
Signed-off-by: James Hogan <[email protected]>
Tested-by: Waldemar Brodkorb <[email protected]>
Cc: Ralf Baechle <[email protected]>
Cc: Maciej W. Rozycki <[email protected]>
Cc: Matthew Fortune <[email protected]>
Cc: Florian Fainelli <[email protected]>
Cc: [email protected]
Patchwork: https://patchwork.linux-mips.org/patch/17890/

0 files changed, 0 insertions, 0 deletions