From 25a491fe349fc52b69ece2ecbcb0b0189decb36f Mon Sep 17 00:00:00 2001
From: Roberto Ierusalimschy <roberto@inf.puc-rio.br>
Date: Wed, 11 Dec 2024 13:56:03 -0300
Subject: [PATCH] OP_SELF restricted to constant short strings

Optimize this opcode for the common case. For long names or method
calls after too many constants, operation can be coded as a move
followed by 'gettable'.
---
 lcode.c           | 43 +++++++++++++++++++++++++++----------------
 ldebug.c          | 15 ++-------------
 lopcodes.h        |  2 +-
 lvm.c             |  6 +++---
 testes/errors.lua |  3 ++-
 5 files changed, 35 insertions(+), 34 deletions(-)

diff --git a/lcode.c b/lcode.c
index 42670794..6c124ff6 100644
--- a/lcode.c
+++ b/lcode.c
@@ -1085,22 +1085,6 @@ void luaK_storevar (FuncState *fs, expdesc *var, expdesc *ex) {
 }
 
 
-/*
-** Emit SELF instruction (convert expression 'e' into 'e:key(e,').
-*/
-void luaK_self (FuncState *fs, expdesc *e, expdesc *key) {
-  int ereg;
-  luaK_exp2anyreg(fs, e);
-  ereg = e->u.info;  /* register where 'e' was placed */
-  freeexp(fs, e);
-  e->u.info = fs->freereg;  /* base register for op_self */
-  e->k = VNONRELOC;  /* self expression has a fixed register */
-  luaK_reserveregs(fs, 2);  /* function and 'self' produced by op_self */
-  codeABRK(fs, OP_SELF, e->u.info, ereg, key);
-  freeexp(fs, key);
-}
-
-
 /*
 ** Negate condition 'e' (where 'e' is a comparison).
 */
@@ -1275,6 +1259,33 @@ static int isSCnumber (expdesc *e, int *pi, int *isfloat) {
 }
 
 
+/*
+** Emit SELF instruction or equivalent: the code will convert
+** expression 'e' into 'e.key(e,'.
+*/
+void luaK_self (FuncState *fs, expdesc *e, expdesc *key) {
+  int ereg, base;
+  luaK_exp2anyreg(fs, e);
+  ereg = e->u.info;  /* register where 'e' (the receiver) was placed */
+  freeexp(fs, e);
+  base = e->u.info = fs->freereg;  /* base register for op_self */
+  e->k = VNONRELOC;  /* self expression has a fixed register */
+  luaK_reserveregs(fs, 2);  /* method and 'self' produced by op_self */
+  lua_assert(key->k == VKSTR);
+  /* is method name a short string in a valid K index? */
+  if (strisshr(key->u.strval) && luaK_exp2K(fs, key)) {
+    /* can use 'self' opcode */
+    luaK_codeABCk(fs, OP_SELF, base, ereg, key->u.info, 0);
+  }
+  else {  /* cannot use 'self' opcode; use move+gettable */
+    luaK_exp2anyreg(fs, key);  /* put method name in a register */
+    luaK_codeABC(fs, OP_MOVE, base + 1, ereg, 0);  /* copy self to base+1 */
+    luaK_codeABC(fs, OP_GETTABLE, base, ereg, key->u.info);  /* get method */
+  }
+  freeexp(fs, key);
+}
+
+
 /*
 ** Create expression 't[k]'. 't' must have its final result already in a
 ** register or upvalue. Upvalues can only be indexed by literal strings.
diff --git a/ldebug.c b/ldebug.c
index ee3ac17f..09ec197c 100644
--- a/ldebug.c
+++ b/ldebug.c
@@ -541,18 +541,6 @@ static void rname (const Proto *p, int pc, int c, const char **name) {
 }
 
 
-/*
-** Find a "name" for a 'C' value in an RK instruction.
-*/
-static void rkname (const Proto *p, int pc, Instruction i, const char **name) {
-  int c = GETARG_C(i);  /* key index */
-  if (GETARG_k(i))  /* is 'c' a constant? */
-    kname(p, c, name);
-  else  /* 'c' is a register */
-    rname(p, pc, c, name);
-}
-
-
 /*
 ** Check whether table being indexed by instruction 'i' is the
 ** environment '_ENV'
@@ -600,7 +588,8 @@ static const char *getobjname (const Proto *p, int lastpc, int reg,
         return isEnv(p, lastpc, i, 0);
       }
       case OP_SELF: {
-        rkname(p, lastpc, i, name);
+        int k = GETARG_C(i);  /* key index */
+        kname(p, k, name);
         return "method";
       }
       default: break;  /* go through to return NULL */
diff --git a/lopcodes.h b/lopcodes.h
index 31f6fac0..7511eb22 100644
--- a/lopcodes.h
+++ b/lopcodes.h
@@ -256,7 +256,7 @@ OP_SETFIELD,/*	A B C	R[A][K[B]:shortstring] := RK(C)			*/
 
 OP_NEWTABLE,/*	A B C k	R[A] := {}					*/
 
-OP_SELF,/*	A B C	R[A+1] := R[B]; R[A] := R[B][RK(C):string]	*/
+OP_SELF,/*	A B C	R[A+1] := R[B]; R[A] := R[B][K[C]:shortstring]	*/
 
 OP_ADDI,/*	A B sC	R[A] := R[B] + sC				*/
 
diff --git a/lvm.c b/lvm.c
index 1c564a71..b6b18a69 100644
--- a/lvm.c
+++ b/lvm.c
@@ -1382,10 +1382,10 @@ void luaV_execute (lua_State *L, CallInfo *ci) {
         StkId ra = RA(i);
         lu_byte tag;
         TValue *rb = vRB(i);
-        TValue *rc = RKC(i);
-        TString *key = tsvalue(rc);  /* key must be a string */
+        TValue *rc = KC(i);
+        TString *key = tsvalue(rc);  /* key must be a short string */
         setobj2s(L, ra + 1, rb);
-        luaV_fastget(rb, key, s2v(ra), luaH_getstr, tag);
+        luaV_fastget(rb, key, s2v(ra), luaH_getshortstr, tag);
         if (tagisempty(tag))
           Protect(luaV_finishget(L, rb, rc, ra, tag));
         vmbreak;
diff --git a/testes/errors.lua b/testes/errors.lua
index 0925fe58..027e1b03 100644
--- a/testes/errors.lua
+++ b/testes/errors.lua
@@ -321,7 +321,8 @@ t = nil
 checkmessage(s.."; aaa = bbb + 1", "global 'bbb'")
 checkmessage("local _ENV=_ENV;"..s.."; aaa = bbb + 1", "global 'bbb'")
 checkmessage(s.."; local t = {}; aaa = t.bbb + 1", "field 'bbb'")
-checkmessage(s.."; local t = {}; t:bbb()", "method 'bbb'")
+-- cannot use 'self' opcode
+checkmessage(s.."; local t = {}; t:bbb()", "field 'bbb'")
 
 checkmessage([[aaa=9
 repeat until 3==3