MIPS: Support MIPS16 interlinking.

doc/install.html

@@ -386,7 +386,7 @@ important to compile with the proper CPU or architecture settings:
 <li>The best way to get consistent results is to specify the correct settings when building the toolchain yourself.</li>
 <li>For a pre-built, generic toolchain add <tt>-mcpu=...</tt> or <tt>-march=...</tt> and other necessary flags to <tt>TARGET_CFLAGS</tt>.</li>
 <li>For ARM it's important to have the correct <tt>-mfloat-abi=...</tt> setting, too. Otherwise LuaJIT may not run at the full performance of your target CPU.</li>
-<li>For MIPS it's important to select a supported ABI (o32 on MIPS32, n64 on MIPS64) and consistently compile your project either with hard-float or soft-float compiler settings. Do not use <tt>-mips16</tt>.</li>
+<li>For MIPS it's important to select a supported ABI (o32 on MIPS32, n64 on MIPS64) and consistently compile your project either with hard-float or soft-float compiler settings.</li>
 </ul>
 <p>
 Here are some examples for targets with a different CPU than the host:

src/jit/dis_mips.lua

@@ -214,7 +214,7 @@ local map_pri = {
   map_cop0,	map_cop1,	false,		map_cop1x,
   "beql|beqzlST0B",	"bnel|bnezlST0B",	"blezlSB",	"bgtzlSB",
   false,	false,		false,		false,
-  map_special2,	false,		false,		map_special3,
+  map_special2,	"jalxJ",	false,		map_special3,
   "lbTSO",	"lhTSO",	"lwlTSO",	"lwTSO",
   "lbuTSO",	"lhuTSO",	"lwrTSO",	false,
   "sbTSO",	"shTSO",	"swlTSO",	"swTSO",

src/lib_jit.c

@@ -721,8 +721,12 @@ static uint32_t jit_cpudetect(lua_State *L)
 #if defined(__GNUC__)
   if (!(flags & JIT_F_MIPSXXR2)) {
     int x;
+#ifdef __mips16
+    x = 0;  /* Runtime detection is difficult. Ensure optimal -march flags. */
+#else
     /* On MIPS32R1 rotr is treated as srl. rotr r2,r2,1 -> srl r2,r2,1. */
     __asm__("li $2, 1\n\t.long 0x00221042\n\tmove %0, $2" : "=r"(x) : : "$2");
+#endif
     if (x) flags |= JIT_F_MIPSXXR2;  /* Either 0x80000000 (R2) or 0 (R1). */
   }
 #endif

src/lj_emit_mips.h

@@ -157,7 +157,8 @@ static void emit_call(ASMState *as, void *target, int needcfa)
   MCode *p = as->mcp;
   *--p = MIPSI_NOP;
   if ((((uintptr_t)target ^ (uintptr_t)p) >> 28) == 0) {
-    *--p = MIPSI_JAL | (((uintptr_t)target >>2) & 0x03ffffffu);
+    *--p = (((uintptr_t)target & 1) ? MIPSI_JALX : MIPSI_JAL) |
+	   (((uintptr_t)target >>2) & 0x03ffffffu);
   } else {  /* Target out of range: need indirect call. */
     *--p = MIPSI_JALR | MIPSF_S(RID_CFUNCADDR);
     needcfa = 1;

src/lj_target_mips.h

@@ -239,6 +239,7 @@ typedef enum MIPSIns {
   MIPSI_B = 0x10000000,
   MIPSI_J = 0x08000000,
   MIPSI_JAL = 0x0c000000,
+  MIPSI_JALX = 0x74000000,
   MIPSI_JR = 0x00000008,
   MIPSI_JALR = 0x0000f809,