cmd/internal/obj/mips, runtime: change REGTMP to R23

Leave R28 to SB register, which will be introduced in CL 19802.

Change-Id: I1cf7a789695c5de664267ec8086bfb0b043ebc14
Reviewed-on: https://go-review.googlesource.com/19863Reviewed-by: Minux Ma <minux@golang.org>

src/cmd/internal/obj/mips/a.out.go

@@ -195,7 +195,7 @@ const (
 	REGRT2   = REG_R2  /* reserved for runtime, duffcopy */
 	REGCTXT  = REG_R22 /* context for closures */
 	REGG     = REG_R30 /* G */
-	REGTMP   = REG_R28 /* used by the linker */
+	REGTMP   = REG_R23 /* used by the linker */
 	FREGRET  = REG_F0
 	FREGZERO = REG_F24 /* both float and double */
 	FREGHALF = REG_F26 /* double */

src/runtime/asm_mips64x.s

@@ -24,8 +24,8 @@ TEXT runtime·rt0_go(SB),NOSPLIT,$0
 	// create istack out of the given (operating system) stack.
 	// _cgo_init may update stackguard.
 	MOVV	$runtime·g0(SB), g
-	MOVV	$(-64*1024), R28
-	ADDV	R28, R29, R1
+	MOVV	$(-64*1024), R23
+	ADDV	R23, R29, R1
 	MOVV	R1, g_stackguard0(g)
 	MOVV	R1, g_stackguard1(g)
 	MOVV	R1, (g_stack+stack_lo)(g)
@@ -299,9 +299,9 @@ TEXT runtime·stackBarrier(SB),NOSPLIT,$0
 // Caution: ugly multiline assembly macros in your future!
 
 #define DISPATCH(NAME,MAXSIZE)		\
-	MOVV	$MAXSIZE, R28;		\
-	SGTU	R1, R28, R28;		\
-	BNE	R28, 3(PC);			\
+	MOVV	$MAXSIZE, R23;		\
+	SGTU	R1, R23, R23;		\
+	BNE	R23, 3(PC);			\
 	MOVV	$NAME(SB), R4;	\
 	JMP	(R4)
 // Note: can't just "BR NAME(SB)" - bad inlining results.

src/runtime/tls_mips64x.s

@@ -11,10 +11,10 @@
 
 // If !iscgo, this is a no-op.
 //
-// NOTE: mcall() assumes this clobbers only R28 (REGTMP).
+// NOTE: mcall() assumes this clobbers only R23 (REGTMP).
 TEXT runtime·save_g(SB),NOSPLIT,$-8-0
-	MOVB	runtime·iscgo(SB), R28
-	BEQ	R28, nocgo
+	MOVB	runtime·iscgo(SB), R23
+	BEQ	R23, nocgo
 
 nocgo:
 	RET