Massively simplify luaK_prepcallfirstarg on the assumption that 'func…

…' is actually not in a register yet, hence we can discharge it into a VRELOC, and put it directly in the correct register. Managing 'e' is also not a PITA under this assumption because we don't have to worry about the function being overwritten.

src/lcode.cpp

@@ -1104,44 +1104,12 @@ void luaK_self (FuncState *fs, expdesc *e, expdesc *key) {
 ** Convert expression 'e' into 'func(e,'.
 */
 void luaK_prepcallfirstarg (FuncState *fs, expdesc *e, expdesc *func) {
-  luaK_exp2anyreg(fs, func);
-  int freg = func->u.reg;  /* register where 'func' was placed */
-  if (e->k == VNIL || e->k == VFALSE || e->k == VTRUE || e->k == VKSTR || e->k == VK || e->k == VKFLT || e->k == VKINT || e->k == VRELOC) {  /* 'e' is yet to be loaded into a register? */
-    freeexp(fs, func);
-    const int basereg = fs->freereg;  /* base register for call */
-    exp2reg(fs, e, basereg + 1);
-    luaK_reserveregs(fs, 2);  /* function and first arg */
-    if (basereg != freg) {  /* ensure function is in correct register */
-      luaK_codeABC(fs, OP_MOVE, basereg, freg, 0);
-    }
-    e->u.reg = basereg;
-    e->k = VNONRELOC;  /* expression has a fixed register */
-  }
-  else {
-    luaK_exp2anyreg(fs, e);
-    int ereg = e->u.reg;  /* register where 'e' was placed */
-    freeexps(fs, e, func);
-    e->u.reg = fs->freereg;  /* base register for call */
-    e->k = VNONRELOC;  /* expression has a fixed register */
-    luaK_reserveregs(fs, 2);  /* function and first arg */
-    if (ereg == e->u.reg) {  /* argument is in the register where the function should be? */
-      if (freg == e->u.reg + 1) {  /* function is in the register where the argument should be? */
-        /* oh dear. we have to swap them around. move function into a temporary register. */
-        luaK_checkstack(fs, 1);
-        int tmpreg = e->u.reg + 2;
-        luaK_codeABC(fs, OP_MOVE, tmpreg, freg, 0);
-        freg = tmpreg;
-      }
-      luaK_codeABC(fs, OP_MOVE, e->u.reg + 1, ereg, 0);  /* move it where it should be */
-      ereg = e->u.reg + 1;  /* and don't do it again */
-    }
-    if (e->u.reg != freg) {  /* ensure function is in correct register */
-      luaK_codeABC(fs, OP_MOVE, e->u.reg, freg, 0);
-    }
-    if (e->u.reg + 1 != ereg) {  /* ensure argument is in correct register */
-      luaK_codeABC(fs, OP_MOVE, e->u.reg + 1, ereg, 0);
-    }
-  }
+  luaK_reserveregs(fs, 2);  /* function and first arg */
+  const int basereg = fs->freereg;  /* base register for call */
+  luaK_exp2reg(fs, e, basereg + 1);
+  luaK_exp2reg(fs, func, basereg);
+  e->u.reg = basereg;
+  e->k = VNONRELOC;  /* expression has a fixed register */
 }