From dfc839625011d6bbc51c9415be4e55a6d4ffe45a Mon Sep 17 00:00:00 2001
From: Benoit Giannangeli <benoit.giannangeli@boursorama.fr>
Date: Mon, 6 Feb 2017 11:30:50 +0100
Subject: TAILCALL

---
 src/lvm.js   | 45 +++++++++++++++++++++++++++++++++++++++++----
 tests/lvm.js | 26 ++++++++++++++++++++++++++
 2 files changed, 67 insertions(+), 4 deletions(-)

diff --git a/src/lvm.js b/src/lvm.js
index 95382b3..e0901c5 100644
--- a/src/lvm.js
+++ b/src/lvm.js
@@ -1,7 +1,9 @@
 /*jshint esversion: 6 */
 "use strict";
 
-const BytecodeParser = require("./lundump.js");
+const assert         = require('assert');
+
+const BytecodeParser = require('./lundump.js');
 const OC             = require('./lopcodes.js');
 const lua            = require('./lua.js');
 const CT             = lua.constant_types;
@@ -358,13 +360,48 @@ class LuaVM {
                     if (b !== 0)
                         L.top = ra+b;
 
-                    this.precall(ra, L.stack[ra], nresults);
-                    ci = L.ci;
-                    continue newframe;
+                    if (this.precall(ra, L.stack[ra], nresults)) {
+                        if (nresults >= 0)
+                            L.top = ci.top;
+                        base = ci.u.l.base;
+                    } else {
+                        ci = L.ci;
+                        continue newframe;
+                    }
 
                     break;
                 }
                 case "OP_TAILCALL": {
+                    if (i.B !== 0) L.top = ra + i.B;
+                    if (this.precall(ra, L.stack[ra], LUA_MULTRET)) {
+                        base = ci.u.l.base;
+                    } else {
+                        /* tail call: put called frame (n) in place of caller one (o) */
+                        let nci = L.ci;
+                        let oci = nci.previous;
+                        let nfunc = nci.func;
+                        let nfuncOff = nci.funcOff;
+                        let ofunc = oci.func;
+                        let ofuncOff = oci.funcOff;
+                        let lim = nci.u.l.base + nfunc.p.numparams;
+                        // TODO close upvalues ?
+                        for (let aux = 0; nfuncOff + aux < lim; aux++)
+                            L.stack[ofuncOff + aux] = L.stack[nfuncOff + aux];
+
+                        oci.u.l.base = ofuncOff + (nci.u.l.base - nfuncOff);
+                        L.top = ofuncOff + (L.top - nfuncOff);
+                        oci.top = L.top;
+                        oci.u.l.savedpc = nci.u.l.savedpc;
+                        oci.pcOff = nci.pcOff;
+                        //TODO callstatus
+                        L.ci = oci;
+                        ci = L.ci;
+                        L.ciOff--;
+
+                        assert(L.top === oci.u.l.base + L.stack[ofuncOff].p.maxstacksize);
+
+                        continue newframe;
+                    }
                     break;
                 }
                 case "OP_RETURN": {
diff --git a/tests/lvm.js b/tests/lvm.js
index 0a71bf8..c454bcf 100644
--- a/tests/lvm.js
+++ b/tests/lvm.js
@@ -219,3 +219,29 @@ test('Multiple return', function (t) {
         "Program output is correct"
     );
 });
+
+
+test('TAILCALL', function (t) {
+    let luaCode = `
+        local f = function (a, b)
+            return a + b
+        end
+
+        return f(1,2)
+    `, vm;
+    
+    t.plan(2);
+
+    t.comment("Running following code: \n" + luaCode);
+
+    t.doesNotThrow(function () {
+        vm = getVM(luaCode);
+        vm.execute();
+    }, "Program executed without errors");
+
+    t.strictEqual(
+        vm.L.stack[vm.L.top - 1].value,
+        3,
+        "Program output is correct"
+    );
+});
\ No newline at end of file
-- 
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