Add SPLIT pass to split 64 bit IR instructions for 32 bit CPUs.

Add generic HIOP instruction for extra backend functionality.
Add support for HIOP to x86 backend.
Use POWI for 64 bit integer x^k, too.
POWI is lowered to a call by SPLIT or the x64 backend.

src/lj_target_x86.h

@@ -193,6 +193,7 @@ typedef enum {
   XI_FLD1 =	0xe8d9,
   XI_FLDLG2 =	0xecd9,
   XI_FLDLN2 =	0xedd9,
+  XI_FDUP =	0xc0d9,  /* Really fld st0. */
   XI_FPOP =	0xd8dd,  /* Really fstp st0. */
   XI_FPOP1 =	0xd9dd,  /* Really fstp st1. */
   XI_FRNDINT =	0xfcd9,
@@ -263,10 +264,17 @@ typedef enum {
   XO_MOVD =	XO_660f(6e),
   XO_MOVDto =	XO_660f(7e),
 
+  XO_FLDd =	XO_(d9), XOg_FLDd = 0,
   XO_FLDq =	XO_(dd), XOg_FLDq = 0,
   XO_FILDd =	XO_(db), XOg_FILDd = 0,
+  XO_FILDq =	XO_(df), XOg_FILDq = 5,
+  XO_FSTPd =	XO_(d9), XOg_FSTPd = 3,
   XO_FSTPq =	XO_(dd), XOg_FSTPq = 3,
   XO_FISTPq =	XO_(df), XOg_FISTPq = 7,
+  XO_FISTTPq =	XO_(dd), XOg_FISTTPq = 1,
+  XO_FADDq =	XO_(dc), XOg_FADDq = 0,
+  XO_FLDCW =	XO_(d9), XOg_FLDCW = 5,
+  XO_FNSTCW =	XO_(d9), XOg_FNSTCW = 7
 } x86Op;
 
 /* x86 opcode groups. */
@@ -278,6 +286,7 @@ typedef uint32_t x86Group;
 #define XG_TOXOi8(xg)	((x86Op)(0x000000fe + (((xg)<<8) & 0xff000000)))
 
 #define XO_ARITH(a)	((x86Op)(0x030000fe + ((a)<<27)))
+#define XO_ARITHw(a)	((x86Op)(0x036600fd + ((a)<<27)))
 
 typedef enum {
   XOg_ADD, XOg_OR, XOg_ADC, XOg_SBB, XOg_AND, XOg_SUB, XOg_XOR, XOg_CMP,