runtime: don't use REP;MOVSB if CPUID doesn't say it is fast

Only use REP;MOVSB if:
 1) The CPUID flag says it is fast, and
 2) The pointers are unaligned
Otherwise, use REP;MOVSQ.

Update #14630

Change-Id: I946b28b87880c08e5eed1ce2945016466c89db66
Reviewed-on: https://go-review.googlesource.com/21300
Reviewed-by: Nigel Tao <nigeltao@golang.org>

src/runtime/asm_386.s

@@ -54,6 +54,7 @@ bad_proc: // show that the program requires MMX.
 has_cpuid:
 	MOVL	$0, AX
 	CPUID
+	MOVL	AX, SI
 	CMPL	AX, $0
 	JE	nocpuinfo
 
@@ -69,6 +70,7 @@ has_cpuid:
 	MOVB	$1, runtime·lfenceBeforeRdtsc(SB)
 notintel:
 
+	// Load EAX=1 cpuid flags
 	MOVL	$1, AX
 	CPUID
 	MOVL	CX, AX // Move to global variable clobbers CX when generating PIC
@@ -79,6 +81,14 @@ notintel:
 	TESTL	$(1<<23), DX	// MMX
 	JZ 	bad_proc
 
+	// Load EAX=7/ECX=0 cpuid flags
+	CMPL	SI, $7
+	JLT	nocpuinfo
+	MOVL	$7, AX
+	MOVL	$0, CX
+	CPUID
+	MOVL	BX, runtime·cpuid_ebx7(SB)
+
 nocpuinfo:	
 
 	// if there is an _cgo_init, call it to let it

src/runtime/asm_amd64.s

@@ -28,6 +28,7 @@ TEXT runtime·rt0_go(SB),NOSPLIT,$0
 	// find out information about the processor we're on
 	MOVQ	$0, AX
 	CPUID
+	MOVQ	AX, SI
 	CMPQ	AX, $0
 	JE	nocpuinfo
 
@@ -42,15 +43,25 @@ TEXT runtime·rt0_go(SB),NOSPLIT,$0
 	JNE	notintel
 	MOVB	$1, runtime·lfenceBeforeRdtsc(SB)
 notintel:
-	// Do nothing.
 
+	// Load EAX=1 cpuid flags
 	MOVQ	$1, AX
 	CPUID
 	MOVL	CX, runtime·cpuid_ecx(SB)
 	MOVL	DX, runtime·cpuid_edx(SB)
+
+	// Load EAX=7/ECX=0 cpuid flags
+	CMPQ	SI, $7
+	JLT	no7
+	MOVL	$7, AX
+	MOVL	$0, CX
+	CPUID
+	MOVL	BX, runtime·cpuid_ebx7(SB)
+no7:
 	// Detect AVX and AVX2 as per 14.7.1  Detection of AVX2 chapter of [1]
 	// [1] 64-ia-32-architectures-software-developer-manual-325462.pdf
 	// http://www.intel.com/content/dam/www/public/us/en/documents/manuals/64-ia-32-architectures-software-developer-manual-325462.pdf
+	MOVL	runtime·cpuid_ecx(SB), CX
 	ANDL    $0x18000000, CX // check for OSXSAVE and AVX bits
 	CMPL    CX, $0x18000000
 	JNE     noavx
@@ -61,12 +72,8 @@ notintel:
 	CMPL    AX, $6 // Check for OS support of YMM registers
 	JNE     noavx
 	MOVB    $1, runtime·support_avx(SB)
-	MOVL    $7, AX
-	MOVL    $0, CX
-	CPUID
-	ANDL    $0x20, BX // check for AVX2 bit
-	CMPL    BX, $0x20
-	JNE     noavx2
+	TESTL   $(1<<5), runtime·cpuid_ebx7(SB) // check for AVX2 bit
+	JEQ     noavx2
 	MOVB    $1, runtime·support_avx2(SB)
 	JMP     nocpuinfo
 noavx:

src/runtime/memmove_386.s

@@ -70,24 +70,29 @@ nosse2:
  * forward copy loop
  */
 forward:
+	// If REP MOVSB isn't fast, don't use it
+	TESTL	$(1<<9), runtime·cpuid_ebx7(SB) // erms, aka enhanced REP MOVSB/STOSB
+	JEQ	fwdBy4
+
 	// Check alignment
 	MOVL	SI, AX
 	ORL	DI, AX
 	TESTL	$3, AX
-	JNE	unaligned_fwd
+	JEQ	fwdBy4
 
-	MOVL	BX, CX
-	SHRL	$2, CX
-	ANDL	$3, BX
-
-	REP;	MOVSL
-	JMP	tail
-
-unaligned_fwd:
+	// Do 1 byte at a time
 	MOVL	BX, CX
 	REP;	MOVSB
 	RET
 
+fwdBy4:
+	// Do 4 bytes at a time
+	MOVL	BX, CX
+	SHRL	$2, CX
+	ANDL	$3, BX
+	REP;	MOVSL
+	JMP	tail
+
 /*
  * check overlap
  */

src/runtime/memmove_amd64.s

@@ -77,25 +77,29 @@ forward:
 	CMPQ	BX, $2048
 	JLS	move_256through2048
 
-	// Check alignment
-	MOVQ	SI, AX
-	ORQ	DI, AX
-	TESTL	$7, AX
-	JNE	unaligned_fwd
+	// If REP MOVSB isn't fast, don't use it
+	TESTL	$(1<<9), runtime·cpuid_ebx7(SB) // erms, aka enhanced REP MOVSB/STOSB
+	JEQ	fwdBy8
 
-	// Aligned - do 8 bytes at a time
+	// Check alignment
+	MOVL	SI, AX
+	ORL	DI, AX
+	TESTL	$7, AX
+	JEQ	fwdBy8
+
+	// Do 1 byte at a time
+	MOVQ	BX, CX
+	REP;	MOVSB
+	RET
+
+fwdBy8:
+	// Do 8 bytes at a time
 	MOVQ	BX, CX
 	SHRQ	$3, CX
 	ANDQ	$7, BX
 	REP;	MOVSQ
 	JMP	tail
 
-unaligned_fwd:
-	// Unaligned - do 1 byte at a time
-	MOVQ	BX, CX
-	REP;	MOVSB
-	RET
-
 back:
 /*
  * check overlap

src/runtime/runtime2.go

@@ -701,6 +701,7 @@ var (
 	// Set on startup in asm_{x86,amd64}.s.
 	cpuid_ecx         uint32
 	cpuid_edx         uint32
+	cpuid_ebx7        uint32
 	lfenceBeforeRdtsc bool
 	support_avx       bool
 	support_avx2      bool