crypto/sha512: remove unnecessary move op, replace with direct add

goos: linux
goarch: riscv64
pkg: crypto/sha512
                    │      o      │                 n                  │
                    │   sec/op    │   sec/op     vs base               │
Hash8Bytes/New-4      3.499µ ± 0%   3.444µ ± 0%  -1.56% (p=0.000 n=10)
Hash8Bytes/Sum384-4   4.012µ ± 0%   3.957µ ± 0%  -1.37% (p=0.000 n=10)
Hash8Bytes/Sum512-4   4.218µ ± 0%   4.162µ ± 0%  -1.32% (p=0.000 n=10)
Hash1K/New-4          17.07µ ± 0%   16.57µ ± 0%  -2.97% (p=0.000 n=10)
Hash1K/Sum384-4       17.59µ ± 0%   17.11µ ± 0%  -2.76% (p=0.000 n=10)
Hash1K/Sum512-4       17.78µ ± 0%   17.30µ ± 0%  -2.72% (p=0.000 n=10)
Hash8K/New-4          112.2µ ± 0%   108.7µ ± 0%  -3.08% (p=0.000 n=10)
Hash8K/Sum384-4       112.7µ ± 0%   109.2µ ± 0%  -3.09% (p=0.000 n=10)
Hash8K/Sum512-4       112.9µ ± 0%   109.4µ ± 0%  -3.07% (p=0.000 n=10)
geomean               19.72µ        19.24µ       -2.44%

                    │      o       │                  n                  │
                    │     B/s      │     B/s       vs base               │
Hash8Bytes/New-4      2.184Mi ± 0%   2.213Mi ± 0%  +1.31% (p=0.000 n=10)
Hash8Bytes/Sum384-4   1.898Mi ± 1%   1.926Mi ± 0%  +1.51% (p=0.000 n=10)
Hash8Bytes/Sum512-4   1.812Mi ± 1%   1.831Mi ± 0%  +1.05% (p=0.000 n=10)
Hash1K/New-4          57.20Mi ± 0%   58.95Mi ± 0%  +3.06% (p=0.000 n=10)
Hash1K/Sum384-4       55.51Mi ± 0%   57.09Mi ± 0%  +2.84% (p=0.000 n=10)
Hash1K/Sum512-4       54.91Mi ± 0%   56.44Mi ± 0%  +2.79% (p=0.000 n=10)
Hash8K/New-4          69.63Mi ± 0%   71.84Mi ± 0%  +3.17% (p=0.000 n=10)
Hash8K/Sum384-4       69.30Mi ± 0%   71.52Mi ± 0%  +3.20% (p=0.000 n=10)
Hash8K/Sum512-4       69.19Mi ± 0%   71.39Mi ± 0%  +3.18% (p=0.000 n=10)
geomean               19.65Mi        20.13Mi       +2.45%

Change-Id: Ib68b934276ec08246d4ae60ef9870c233f0eac69
Reviewed-on: https://go-review.googlesource.com/c/go/+/665595


LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Joel Sing <joel@sing.id.au>
Reviewed-by: Roland Shoemaker <roland@golang.org>

src/crypto/internal/fips140/sha512/sha512block_riscv64.s

@@ -138,9 +138,8 @@
 #define SHA512ROUND(index, a, b, c, d, e, f, g, h) \
 	SHA512T1(index, e, f, g, h); \
 	SHA512T2(a, b, c); \
-	MOV	X6, h; \
 	ADD	X5, d; \
-	ADD	X5, h
+	ADD	X6, X5, h
 
 #define SHA512ROUND0(index, a, b, c, d, e, f, g, h) \
 	MSGSCHEDULE0(index); \