Remove Roblox-specific mutable globals (#185)

Instead the code that calls the compiler needs to use Compiler::mutableGlobals to disable GETIMPORT optimization.

Compiler/include/Luau/Compiler.h

@@ -36,6 +36,10 @@ struct CompileOptions
     // global builtin to construct vectors; disabled by default
     const char* vectorLib = nullptr;
     const char* vectorCtor = nullptr;
+
+    // array of globals that are mutable; disables the import optimization for fields accessed through them
+    // use NULL to end the array
+    const char** mutableGlobals = nullptr;
 };
 
 class CompileError : public std::exception

Compiler/src/Compiler.cpp

@@ -13,6 +13,7 @@
 LUAU_FASTFLAGVARIABLE(LuauPreloadClosures, false)
 LUAU_FASTFLAGVARIABLE(LuauPreloadClosuresFenv, false)
 LUAU_FASTFLAGVARIABLE(LuauPreloadClosuresUpval, false)
+LUAU_FASTFLAGVARIABLE(LuauGenericSpecialGlobals, false)
 LUAU_FASTFLAG(LuauIfElseExpressionBaseSupport)
 
 namespace Luau
@@ -1277,7 +1278,7 @@ struct Compiler
     {
         const Global* global = globals.find(expr->name);
 
-        return options.optimizationLevel >= 1 && (!global || (!global->written && !global->special));
+        return options.optimizationLevel >= 1 && (!global || (!global->written && !global->writable));
     }
 
     void compileExprIndexName(AstExprIndexName* expr, uint8_t target)
@@ -3447,7 +3448,7 @@ struct Compiler
 
     struct Global
     {
-        bool special = false;
+        bool writable = false;
         bool written = false;
     };
 
@@ -3505,7 +3506,7 @@ struct Compiler
             {
                 Global* g = globals.find(object->name);
 
-                return !g || (!g->special && !g->written) ? Builtin{object->name, expr->index} : Builtin();
+                return !g || (!g->writable && !g->written) ? Builtin{object->name, expr->index} : Builtin();
             }
             else
             {
@@ -3703,13 +3704,26 @@ void compileOrThrow(BytecodeBuilder& bytecode, AstStatBlock* root, const AstName
 
     Compiler compiler(bytecode, options);
 
-    // since access to some global objects may result in values that change over time, we block table imports
+    // since access to some global objects may result in values that change over time, we block imports from non-readonly tables
+    if (FFlag::LuauGenericSpecialGlobals)
+    {
+        if (AstName name = names.get("_G"); name.value)
+            compiler.globals[name].writable = true;
+
+        if (options.mutableGlobals)
+            for (const char** ptr = options.mutableGlobals; *ptr != NULL; ++ptr)
+            {
+                if (AstName name = names.get(*ptr); name.value)
+                    compiler.globals[name].writable = true;
+            }
+    }
+    else
+    {
         for (const char* global : kSpecialGlobals)
         {
-        AstName name = names.get(global);
+            if (AstName name = names.get(global); name.value)
-
+                compiler.globals[name].writable = true;
-        if (name.value)
+        }
-            compiler.globals[name].special = true;
     }
 
     // this visitor traverses the AST to analyze mutability of locals/globals, filling Local::written and Global::written

tests/Compiler.test.cpp

@@ -13,6 +13,7 @@
 LUAU_FASTFLAG(LuauPreloadClosures)
 LUAU_FASTFLAG(LuauPreloadClosuresFenv)
 LUAU_FASTFLAG(LuauPreloadClosuresUpval)
+LUAU_FASTFLAG(LuauGenericSpecialGlobals)
 
 using namespace Luau;
 
@@ -3670,4 +3671,118 @@ RETURN R0 0
 )");
 }
 
+TEST_CASE("LuauGenericSpecialGlobals")
+{
+    const char* source = R"(
+print()
+Game.print()
+Workspace.print()
+_G.print()
+game.print()
+plugin.print()
+script.print()
+shared.print()
+workspace.print()
+)";
+
+    {
+        ScopedFastFlag genericSpecialGlobals{"LuauGenericSpecialGlobals", false};
+
+        // Check Roblox globals are here
+        CHECK_EQ("\n" + compileFunction0(source), R"(
+GETIMPORT R0 1
+CALL R0 0 0
+GETIMPORT R1 3
+GETTABLEKS R0 R1 K0
+CALL R0 0 0
+GETIMPORT R1 5
+GETTABLEKS R0 R1 K0
+CALL R0 0 0
+GETIMPORT R1 7
+GETTABLEKS R0 R1 K0
+CALL R0 0 0
+GETIMPORT R1 9
+GETTABLEKS R0 R1 K0
+CALL R0 0 0
+GETIMPORT R1 11
+GETTABLEKS R0 R1 K0
+CALL R0 0 0
+GETIMPORT R1 13
+GETTABLEKS R0 R1 K0
+CALL R0 0 0
+GETIMPORT R1 15
+GETTABLEKS R0 R1 K0
+CALL R0 0 0
+GETIMPORT R1 17
+GETTABLEKS R0 R1 K0
+CALL R0 0 0
+RETURN R0 0
+)");
+    }
+
+    ScopedFastFlag genericSpecialGlobals{"LuauGenericSpecialGlobals", true};
+
+    // Check Roblox globals are no longer here
+    CHECK_EQ("\n" + compileFunction0(source), R"(
+GETIMPORT R0 1
+CALL R0 0 0
+GETIMPORT R0 3
+CALL R0 0 0
+GETIMPORT R0 5
+CALL R0 0 0
+GETIMPORT R1 7
+GETTABLEKS R0 R1 K0
+CALL R0 0 0
+GETIMPORT R0 9
+CALL R0 0 0
+GETIMPORT R0 11
+CALL R0 0 0
+GETIMPORT R0 13
+CALL R0 0 0
+GETIMPORT R0 15
+CALL R0 0 0
+GETIMPORT R0 17
+CALL R0 0 0
+RETURN R0 0
+)");
+
+    // Check we can add them back
+    Luau::BytecodeBuilder bcb;
+    bcb.setDumpFlags(Luau::BytecodeBuilder::Dump_Code);
+    Luau::CompileOptions options;
+    const char* mutableGlobals[] = {"Game", "Workspace", "game", "plugin", "script", "shared", "workspace", NULL};
+    options.mutableGlobals = &mutableGlobals[0];
+    Luau::compileOrThrow(bcb, source, options);
+
+    CHECK_EQ("\n" + bcb.dumpFunction(0), R"(
+GETIMPORT R0 1
+CALL R0 0 0
+GETIMPORT R1 3
+GETTABLEKS R0 R1 K0
+CALL R0 0 0
+GETIMPORT R1 5
+GETTABLEKS R0 R1 K0
+CALL R0 0 0
+GETIMPORT R1 7
+GETTABLEKS R0 R1 K0
+CALL R0 0 0
+GETIMPORT R1 9
+GETTABLEKS R0 R1 K0
+CALL R0 0 0
+GETIMPORT R1 11
+GETTABLEKS R0 R1 K0
+CALL R0 0 0
+GETIMPORT R1 13
+GETTABLEKS R0 R1 K0
+CALL R0 0 0
+GETIMPORT R1 15
+GETTABLEKS R0 R1 K0
+CALL R0 0 0
+GETIMPORT R1 17
+GETTABLEKS R0 R1 K0
+CALL R0 0 0
+RETURN R0 0
+)");
+}
+
 TEST_SUITE_END();