internal/cpu: add a detection for Neoverse(N2, V2) cores

The memmove implementation relies on the variable
runtime.arm64UseAlignedLoads to select fastest code
path. Considering Neoverse N2 and V2 cores prefer aligned
loads, this patch adds code to detect them for
memmove performance.

And this patch uses a new variable ARM64.IsNeoverse to
represent all Neoverse cores, removing the more specific
versions.

Change-Id: I9e06eae01a0325a0b604ac6af1e55711dd6133f7
Reviewed-on: https://go-review.googlesource.com/c/go/+/487815
Reviewed-by: Joel Sing <joel@sing.id.au>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Run-TryBot: Fannie Zhang <Fannie.Zhang@arm.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

src/internal/cpu/cpu.go

@@ -57,18 +57,17 @@ var ARM struct {
 // The booleans in ARM64 contain the correspondingly named cpu feature bit.
 // The struct is padded to avoid false sharing.
 var ARM64 struct {
-	_            CacheLinePad
-	HasAES       bool
-	HasPMULL     bool
-	HasSHA1      bool
-	HasSHA2      bool
-	HasSHA512    bool
-	HasCRC32     bool
-	HasATOMICS   bool
-	HasCPUID     bool
-	IsNeoverseN1 bool
-	IsNeoverseV1 bool
-	_            CacheLinePad
+	_          CacheLinePad
+	HasAES     bool
+	HasPMULL   bool
+	HasSHA1    bool
+	HasSHA2    bool
+	HasSHA512  bool
+	HasCRC32   bool
+	HasATOMICS bool
+	HasCPUID   bool
+	IsNeoverse bool
+	_          CacheLinePad
 }
 
 var MIPS64X struct {

src/internal/cpu/cpu_arm64.go

@@ -19,8 +19,7 @@ func doinit() {
 		{Name: "crc32", Feature: &ARM64.HasCRC32},
 		{Name: "atomics", Feature: &ARM64.HasATOMICS},
 		{Name: "cpuid", Feature: &ARM64.HasCPUID},
-		{Name: "isNeoverseN1", Feature: &ARM64.IsNeoverseN1},
-		{Name: "isNeoverseV1", Feature: &ARM64.IsNeoverseV1},
+		{Name: "isNeoverse", Feature: &ARM64.IsNeoverse},
 	}
 
 	// arm64 uses different ways to detect CPU features at runtime depending on the operating system.

src/internal/cpu/cpu_arm64_hwcap.go

@@ -39,22 +39,24 @@ func hwcapInit(os string) {
 	// TODO(elias.naur): Only disable the optimization on bad chipsets on android.
 	ARM64.HasATOMICS = isSet(HWCap, hwcap_ATOMICS) && os != "android"
 
-	// Check to see if executing on a NeoverseN1 and in order to do that,
+	// Check to see if executing on a Neoverse core and in order to do that,
 	// check the AUXV for the CPUID bit. The getMIDR function executes an
 	// instruction which would normally be an illegal instruction, but it's
-	// trapped by the kernel, the value sanitized and then returned. Without
-	// the CPUID bit the kernel will not trap the instruction and the process
-	// will be terminated with SIGILL.
+	// trapped by the kernel, the value sanitized and then returned.
+	// Without the CPUID bit the kernel will not trap the instruction and the
+	// process will be terminated with SIGILL.
 	if ARM64.HasCPUID {
 		midr := getMIDR()
 		part_num := uint16((midr >> 4) & 0xfff)
 		implementor := byte((midr >> 24) & 0xff)
 
-		if implementor == 'A' && part_num == 0xd0c {
-			ARM64.IsNeoverseN1 = true
-		}
-		if implementor == 'A' && part_num == 0xd40 {
-			ARM64.IsNeoverseV1 = true
+		// d0c - NeoverseN1
+		// d40 - NeoverseV1
+		// d49 - NeoverseN2
+		// d4f - NeoverseV2
+		if implementor == 'A' && (part_num == 0xd0c || part_num == 0xd40 ||
+			part_num == 0xd49 || part_num == 0xd4f) {
+			ARM64.IsNeoverse = true
 		}
 	}
 }

src/runtime/cpuflags_arm64.go

@@ -11,7 +11,7 @@ import (
 var arm64UseAlignedLoads bool
 
 func init() {
-	if cpu.ARM64.IsNeoverseN1 || cpu.ARM64.IsNeoverseV1 {
+	if cpu.ARM64.IsNeoverse {
 		arm64UseAlignedLoads = true
 	}
 }