cmd/compile: intrinsify sync/atomic for amd64

Uses the same implementation as runtime/internal/atomic.

Reorganize the intrinsic detector to make it more table-driven.

Also works on amd64p32.

Change-Id: I7a5238951d6018d7d5d1bc01f339f6ee9282b2d0
Reviewed-on: https://go-review.googlesource.com/28076Reviewed-by: Cherry Zhang <cherryyz@google.com>

src/sync/atomic/asm_amd64.s

@@ -2,6 +2,9 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// Note: some of these functions are semantically inlined
+// by the compiler (in src/cmd/compile/internal/gc/ssa.go).
+
 // +build !race
 
 #include "textflag.h"

src/sync/atomic/asm_amd64p32.s

@@ -2,6 +2,9 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// Note: some of these functions are semantically inlined
+// by the compiler (in src/cmd/compile/internal/gc/ssa.go).
+
 #include "textflag.h"
 
 TEXT ·SwapInt32(SB),NOSPLIT,$0-12
@@ -50,9 +53,6 @@ TEXT ·CompareAndSwapInt64(SB),NOSPLIT,$0-25
 
 TEXT ·CompareAndSwapUint64(SB),NOSPLIT,$0-25
 	MOVL	addr+0(FP), BX
-	TESTL	$7, BX
-	JZ	2(PC)
-	MOVL	0, BX // crash with nil ptr deref
 	MOVQ	old+8(FP), AX
 	MOVQ	new+16(FP), CX
 	LOCK
@@ -81,9 +81,6 @@ TEXT ·AddInt64(SB),NOSPLIT,$0-24
 
 TEXT ·AddUint64(SB),NOSPLIT,$0-24
 	MOVL	addr+0(FP), BX
-	TESTL	$7, BX
-	JZ	2(PC)
-	MOVL	0, BX // crash with nil ptr deref
 	MOVQ	delta+8(FP), AX
 	MOVQ	AX, CX
 	LOCK
@@ -106,9 +103,6 @@ TEXT ·LoadInt64(SB),NOSPLIT,$0-16
 
 TEXT ·LoadUint64(SB),NOSPLIT,$0-16
 	MOVL	addr+0(FP), AX
-	TESTL	$7, AX
-	JZ	2(PC)
-	MOVL	0, AX // crash with nil ptr deref
 	MOVQ	0(AX), AX
 	MOVQ	AX, val+8(FP)
 	RET
@@ -136,9 +130,6 @@ TEXT ·StoreInt64(SB),NOSPLIT,$0-16
 
 TEXT ·StoreUint64(SB),NOSPLIT,$0-16
 	MOVL	addr+0(FP), BX
-	TESTL	$7, BX
-	JZ	2(PC)
-	MOVL	0, BX // crash with nil ptr deref
 	MOVQ	val+8(FP), AX
 	XCHGQ	AX, 0(BX)
 	RET

src/sync/atomic/atomic_test.go

@@ -1392,6 +1392,10 @@ func TestUnaligned64(t *testing.T) {
 	if unsafe.Sizeof(int(0)) != 4 {
 		t.Skip("test only runs on 32-bit systems")
 	}
+	if runtime.GOARCH == "amd64p32" {
+		// amd64p32 can handle unaligned atomics.
+		t.Skip("test not needed on amd64p32")
+	}
 
 	x := make([]uint32, 4)
 	p := (*uint64)(unsafe.Pointer(&x[1])) // misaligned