cmd/internal/obj/mips: add WSBH/DSBH/DSHD instructions
Add support for WSBH/DSBH/DSHD instructions, which are introduced in mips{32,64}r2.
WSBH reverse bytes within halfwords for 32-bit word, DSBH reverse bytes within halfwords for 64-bit doubleword, and DSHD reverse halfwords within doublewords. These instructions can be used to optimize byte swaps.
Ref: The MIPS64 Instruction Set, Revision 5.04: https://s3-eu-west-1.amazonaws.com/downloads-mips/documents/MD00087-2B-MIPS64BIS-AFP-05.04.pdf
Updates #60072
Change-Id: I31c043150fe8ac03027f413ef4cb2f3e435775e1
Reviewed-on: https://go-review.googlesource.com/c/go/+/493816
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Joel Sing <joel@sing.id.au>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Run-TryBot: Joel Sing <joel@sing.id.au>
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