Add volatile XLOADs.

src/lj_ir.h

@@ -206,7 +206,8 @@ IRFLDEF(FLENUM)
 
 /* XLOAD mode, stored in op2. */
 #define IRXLOAD_READONLY	1	/* Load from read-only data. */
-#define IRXLOAD_UNALIGNED	2	/* Unaligned load. */
+#define IRXLOAD_VOLATILE	2	/* Load from volatile data. */
+#define IRXLOAD_UNALIGNED	4	/* Unaligned load. */
 
 /* CONV mode, stored in op2. */
 #define IRCONV_SRCMASK		0x001f	/* Source IRType. */

src/lj_opt_mem.c

@@ -669,6 +669,8 @@ TRef LJ_FASTCALL lj_opt_fwd_xload(jit_State *J)
 
   if ((fins->op2 & IRXLOAD_READONLY))
     goto cselim;
+  if ((fins->op2 & IRXLOAD_VOLATILE))
+    goto doemit;
 
   /* Search for conflicting stores. */
   ref = J->chain[IR_XSTORE];
@@ -721,7 +723,8 @@ cselim:
     xr = IR(xref);
     goto retry;  /* Retry with the reassociated reference. */
   }
-  return lj_ir_emit(J);
+doemit:
+  return EMITFOLD;
 }
 
 /* XSTORE elimination. */