runtime: use internal/cpu.X86.HasAVX2 instead of support_avx2

After CL 104636 cpu.X86.HasAVX is set early enough that it can be used
in runtime·memclrNoHeapPointers. Add an offset to use in assembly and
replace the only occurence of support_avx2.

Change-Id: Icada62efeb3e24d71251d55623a8a8602364c9a8
Reviewed-on: https://go-review.googlesource.com/106595
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Ilya Tocar <ilya.tocar@intel.com>

src/runtime/asm_386.s

@@ -184,11 +184,6 @@ eax7:
 	MOVL	$0, CX
 	CPUID
 
-	// If OS support for XMM and YMM is not present
-	// support_avx2 will be set back to false later.
-	TESTL	$(1<<5), BX
-	SETNE	runtime·support_avx2(SB)
-
 	TESTL	$(1<<9), BX // ERMS
 	SETNE	runtime·support_erms(SB)
 
@@ -197,16 +192,13 @@ osavx:
 	// for XMM and YMM OS support.
 #ifndef GOOS_nacl
 	CMPB	runtime·support_osxsave(SB), $1
-	JNE	noavx
+	JNE	nocpuinfo
 	MOVL	$0, CX
 	// For XGETBV, OSXSAVE bit is required and sufficient
 	XGETBV
 	ANDL	$6, AX
 	CMPL	AX, $6 // Check for OS support of XMM and YMM registers.
-	JE nocpuinfo
 #endif
-noavx:
-	MOVB $0, runtime·support_avx2(SB)
 
 nocpuinfo:
 	// if there is an _cgo_init, call it to let it

src/runtime/asm_amd64.s

@@ -147,25 +147,17 @@ eax7:
 	MOVL	$0, CX
 	CPUID
 
-	// If OS support for XMM and YMM is not present
-	// support_avx2 will be set back to false later.
-	TESTL	$(1<<5), BX
-	SETNE	runtime·support_avx2(SB)
-
 	TESTL	$(1<<9), BX // ERMS
 	SETNE	runtime·support_erms(SB)
 
 osavx:
 	CMPB	runtime·support_osxsave(SB), $1
-	JNE	noavx
+	JNE	nocpuinfo
 	MOVL	$0, CX
 	// For XGETBV, OSXSAVE bit is required and sufficient
 	XGETBV
 	ANDL	$6, AX
 	CMPL	AX, $6 // Check for OS support of XMM and YMM registers.
-	JE nocpuinfo
-noavx:
-	MOVB $0, runtime·support_avx2(SB)
 
 nocpuinfo:
 	// if there is an _cgo_init, call it.

src/runtime/asm_amd64p32.s

@@ -67,11 +67,6 @@ eax7:
 	MOVL	$0, CX
 	CPUID
 
-	// If OS support for XMM and YMM is not present
-	// support_avx2 will be set back to false later.
-	TESTL	$(1<<5), BX
-	SETNE	runtime·support_avx2(SB)
-
 	TESTL	$(1<<9), BX // ERMS
 	SETNE	runtime·support_erms(SB)
 
@@ -80,16 +75,13 @@ osavx:
 	// for XMM and YMM OS support.
 #ifndef GOOS_nacl
 	CMPB	runtime·support_osxsave(SB), $1
-	JNE	noavx
+	JNE	nocpuinfo
 	MOVL	$0, CX
 	// For XGETBV, OSXSAVE bit is required and sufficient
 	XGETBV
 	ANDL	$6, AX
 	CMPL	AX, $6 // Check for OS support of XMM and YMM registers.
-	JE nocpuinfo
 #endif
-noavx:
-	MOVB $0, runtime·support_avx2(SB)
 
 nocpuinfo:
 

src/runtime/cpuflags_amd64.go

@@ -4,7 +4,15 @@
 
 package runtime
 
-import "internal/cpu"
+import (
+	"internal/cpu"
+	"unsafe"
+)
+
+// Offsets into internal/cpu records for use in assembly.
+const (
+	offsetX86HasAVX2 = unsafe.Offsetof(cpu.X86.HasAVX2)
+)
 
 var useAVXmemmove bool
 

src/runtime/memclr_amd64.s

@@ -4,6 +4,7 @@
 
 // +build !plan9
 
+#include "go_asm.h"
 #include "textflag.h"
 
 // NOTE: Windows externalthreadhandler expects memclr to preserve DX.
@@ -36,7 +37,7 @@ tail:
 	JBE	_65through128
 	CMPQ	BX, $256
 	JBE	_129through256
-	CMPB	runtime·support_avx2(SB), $1
+	CMPB	internal∕cpu·X86+const_offsetX86HasAVX2(SB), $1
 	JE loop_preheader_avx2
 	// TODO: use branch table and BSR to make this just a single dispatch
 	// TODO: for really big clears, use MOVNTDQ, even without AVX2.

src/runtime/runtime2.go

@@ -779,7 +779,6 @@ var (
 	processorVersionInfo uint32
 	isIntel              bool
 	lfenceBeforeRdtsc    bool
-	support_avx2         bool
 	support_erms         bool
 	support_osxsave      bool
 	support_popcnt       bool