cmd/compile: fix mips64 instruction UNPREDICTABLE bug
cmd/compile: fix mips64 instruction UNPREDICTABLE bug

Replace addu with a sll instruction with a definite behavior (sll will discard the upper 32 bits of the 64 bits, then do sign extensions, with certain behavior). It won't have any UNPREDICTABLE expectation.

Fixes #30459

Change-Id: Id79085c28c5cc4f86939b4ef08ef4bff46077c45
GitHub-Last-Rev: 03569796a9a64ed6c7d56a5bca966fc62c89b4ff
GitHub-Pull-Request: golang/go#30461
Reviewed-on: https://go-review.googlesource.com/c/go/+/164758
Reviewed-by: Cherry Zhang <d62e63aa42ce272d7b6a5055d97e942b33a34679@google.com>
Run-TryBot: Cherry Zhang <d62e63aa42ce272d7b6a5055d97e942b33a34679@google.com>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>

CAFxX/go,josharian/go,josharian/go,golang/go,akutz/go,nawawi/go,akutz/go,nawawi/go,cloudflare/go,akutz/go,golang/go,josharian/go,CAFxX/go,nawawi/go,cloudflare/go,akutz/go,cloudflare/go,CAFxX/go,akutz/go,josharian/go,akutz/go,cloudflare/go,CAFxX/go,CAFxX/go,CAFxX/go,golang/go,cloudflare/go,golang/go,cloudflare/go,nawawi/go,josharian/go,nawawi/go,cloudflare/go,golang/go,CAFxX/go,akutz/go,golang/go,golang/go,akutz/go,CAFxX/go,josharian/go,nawawi/go,nawawi/go,golang/go,josharian/go,cloudflare/go,josharian/go,nawawi/go