runtime: rewrite lfstack packing/unpacking to look more like that in Go

    Reviewed-on: https://go-review.googlesource.com/13037

From-SVN: r228057

gcc/go/gofrontend/MERGE

-e069d4417a692c1261df99fe3323277e1a0193d2
+2087b95180caea3477647c449772b7fecc01a71c
 
 The first line of this file holds the git revision number of the last
 merge done from the gofrontend repository.

libgo/runtime/lfstack.goc

@@ -9,25 +9,41 @@ package runtime
 #include "arch.h"
 
 #if __SIZEOF_POINTER__ == 8
+// SPARC64 and Solaris on AMD64 uses all 64 bits of virtual addresses.
+// Use low-order three bits as ABA counter.
+// http://docs.oracle.com/cd/E19120-01/open.solaris/816-5138/6mba6ua5p/index.html
+# if defined(__sparc__) || (defined(__sun__) && defined(__amd64__))
+static inline uint64 lfPack(LFNode *node, uintptr cnt) {
+	return ((uint64)(node)) | ((cnt)&7);
+}
+static inline LFNode* lfUnpack(uint64 val) {
+	return (LFNode*)(val&~7);
+}
+# else
+#  if defined(__aarch64__)
+// Depending on the kernel options, pointers on arm64 can have up to 48 significant
+// bits (see https://www.kernel.org/doc/Documentation/arm64/memory.txt).
+#   define PTR_BITS 48
+#  else
 // Amd64 uses 48-bit virtual addresses, 47-th bit is used as kernel/user flag.
 // So we use 17msb of pointers as ABA counter.
 #   define PTR_BITS 47
+#  endif
+# endif
+# define CNT_BITS (64 - PTR_BITS + 3)
+static inline uint64 lfPack(LFNode *node, uintptr cnt) {
+	return ((uint64)(node)<<(64-PTR_BITS)) | (cnt&(((1<<CNT_BITS)-1)));
+}
+static inline LFNode* lfUnpack(uint64 val) {
+	return (LFNode*)((val >> CNT_BITS) << 3);
+}
 #else
-# define PTR_BITS 32
-#endif
-#define PTR_MASK ((1ull<<PTR_BITS)-1)
-#define CNT_MASK (0ull-1)
-
-#if __SIZEOF_POINTER__ == 8 && (defined(__sparc__) || (defined(__sun__) && defined(__amd64__)))
-// SPARC64 and Solaris on AMD64 uses all 64 bits of virtual addresses.
-// Use low-order three bits as ABA counter.
-// http://docs.oracle.com/cd/E19120-01/open.solaris/816-5138/6mba6ua5p/index.html
-#undef PTR_BITS
-#undef CNT_MASK
-#undef PTR_MASK
-#define PTR_BITS 0
-#define CNT_MASK 7
-#define PTR_MASK ((0ull-1)<<3)
+static inline uint64 lfPack(LFNode *node, uintptr cnt) {
+	return ((uint64)(uintptr)(node)<<32) | cnt;
+}
+static inline LFNode* lfUnpack(uint64 val) {
+	return (LFNode*)(uintptr)(val >> 32);
+}
 #endif
 
 void
@@ -35,16 +51,16 @@ runtime_lfstackpush(uint64 *head, LFNode *node)
 {
 	uint64 old, new;
 
-	if((uintptr)node != ((uintptr)node&PTR_MASK)) {
+	if(node != lfUnpack(lfPack(node, 0))) {
 		runtime_printf("p=%p\n", node);
 		runtime_throw("runtime_lfstackpush: invalid pointer");
 	}
 
 	node->pushcnt++;
-	new = (uint64)(uintptr)node|(((uint64)node->pushcnt&CNT_MASK)<<PTR_BITS);
+	new = lfPack(node, node->pushcnt);
 	for(;;) {
 		old = runtime_atomicload64(head);
-		node->next = (LFNode*)(uintptr)(old&PTR_MASK);
+		node->next = lfUnpack(old);
 		if(runtime_cas64(head, old, new))
 			break;
 	}
@@ -60,11 +76,11 @@ runtime_lfstackpop(uint64 *head)
 		old = runtime_atomicload64(head);
 		if(old == 0)
 			return nil;
-		node = (LFNode*)(uintptr)(old&PTR_MASK);
+		node = lfUnpack(old);
 		node2 = runtime_atomicloadp(&node->next);
 		new = 0;
 		if(node2 != nil)
-			new = (uint64)(uintptr)node2|(((uint64)node2->pushcnt&CNT_MASK)<<PTR_BITS);
+			new = lfPack(node2, node2->pushcnt);
 		if(runtime_cas64(head, old, new))
 			return node;
 	}