vendor: update golang.org/x/crypto/chacha20poly1305

Updates golang.org/x/crypto/chacha20poly1305 to rev cb497ae for:
- chacha20poly1305: fix detection of BMI on amd64 (https://golang.org/cl/34852)
- chacha20poly1305: fix typos (https://golang.org/cl/34536)
- chacha20poly1305: fix typos (https://golang.org/cl/33855)
- chacha20poly1305: fix build constraints (https://golang.org/cl/32391)

Change-Id: I3a608b5e21b3a72b5aaa5d0afe6c6cffbb1d6fc1
Reviewed-on: https://go-review.googlesource.com/34871
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/vendor/golang_org/x/crypto/chacha20poly1305/chacha20poly1305_amd64.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build amd64,go1.7
+// +build go1.7,amd64,!gccgo,!appengine
 
 package chacha20poly1305
 

src/vendor/golang_org/x/crypto/chacha20poly1305/chacha20poly1305_amd64.s

@@ -4,7 +4,7 @@
 
 // This file was originally from https://golang.org/cl/24717 by Vlad Krasnov of CloudFlare.
 
-// +build go1.7
+// +build go1.7,amd64,!gccgo,!appengine
 
 #include "textflag.h"
 // General register allocation
@@ -280,9 +280,14 @@ TEXT ·chacha20Poly1305Open(SB), 0, $288-97
 	// Check for AVX2 support
 	CMPB runtime·support_avx2(SB), $0
 	JE   noavx2bmi2Open
-	CMPB runtime·support_bmi2(SB), $1  // for MULXQ
-	JE  chacha20Poly1305Open_AVX2
+
+	// Check BMI2 bit for MULXQ.
+	// runtime·cpuid_ebx7 is always available here
+	// because it passed avx2 check
+	TESTL $(1<<8), runtime·cpuid_ebx7(SB)
+	JNE   chacha20Poly1305Open_AVX2
 noavx2bmi2Open:
+
 	// Special optimization, for very short buffers
 	CMPQ inl, $128
 	JBE  openSSE128 // About 16% faster
@@ -1489,9 +1494,14 @@ TEXT ·chacha20Poly1305Seal(SB), 0, $288-96
 	// Check for AVX2 support
 	CMPB runtime·support_avx2(SB), $0
 	JE   noavx2bmi2Seal
-	CMPB runtime·support_bmi2(SB), $1  // for MULXQ
-	JE   chacha20Poly1305Seal_AVX2
+
+	// Check BMI2 bit for MULXQ.
+	// runtime·cpuid_ebx7 is always available here
+	// because it passed avx2 check
+	TESTL $(1<<8), runtime·cpuid_ebx7(SB)
+	JNE   chacha20Poly1305Seal_AVX2
 noavx2bmi2Seal:
+
 	// Special optimization, for very short buffers
 	CMPQ inl, $128
 	JBE  sealSSE128 // About 15% faster
@@ -1695,7 +1705,7 @@ sealSSETail64:
 	MOVO  D1, ctr0Store
 
 sealSSETail64LoopA:
-	// Perform ChaCha rounds, while hashing the prevsiosly encrpyted ciphertext
+	// Perform ChaCha rounds, while hashing the previously encrypted ciphertext
 	polyAdd(0(oup))
 	polyMul
 	LEAQ 16(oup), oup
@@ -1729,7 +1739,7 @@ sealSSETail128:
 	MOVO A0, A1; MOVO B0, B1; MOVO C0, C1; MOVO D0, D1; PADDL ·sseIncMask<>(SB), D1; MOVO D1, ctr1Store
 
 sealSSETail128LoopA:
-	// Perform ChaCha rounds, while hashing the prevsiosly encrpyted ciphertext
+	// Perform ChaCha rounds, while hashing the previously encrypted ciphertext
 	polyAdd(0(oup))
 	polyMul
 	LEAQ 16(oup), oup
@@ -1775,7 +1785,7 @@ sealSSETail192:
 	MOVO A1, A2; MOVO B1, B2; MOVO C1, C2; MOVO D1, D2; PADDL ·sseIncMask<>(SB), D2; MOVO D2, ctr2Store
 
 sealSSETail192LoopA:
-	// Perform ChaCha rounds, while hashing the prevsiosly encrpyted ciphertext
+	// Perform ChaCha rounds, while hashing the previously encrypted ciphertext
 	polyAdd(0(oup))
 	polyMul
 	LEAQ 16(oup), oup

src/vendor/golang_org/x/crypto/chacha20poly1305/chacha20poly1305_noasm.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build !amd64 !go1.7
+// +build !amd64 !go1.7 gccgo appengine
 
 package chacha20poly1305