- Added the TAIL instruction to perform a CALL and a RET in the same instruction. The called

function will pass its results directly to this function's caller. Eventually, this should
  be changed to do a proper tail call for scripted functions.

SVN r3769 (scripting)

src/thingdef/thingdef.cpp

@@ -300,8 +300,7 @@ static void FinishThingdef()
 				p->Emit(&buildit);
 				delete p;
 			}
-			buildit.Emit(OP_CALL_K, buildit.GetConstantAddress(tcall->Function, ATAG_OBJECT), NAP + j, 0);
-			buildit.Emit(OP_RET, 0, REGT_NIL, 0);
+			buildit.Emit(OP_TAIL_K, buildit.GetConstantAddress(tcall->Function, ATAG_OBJECT), NAP + j, 0);
 			VMScriptFunction *sfunc = buildit.MakeFunction();
 			sfunc->NumArgs = NAP;
 			func = sfunc;

src/zscript/vmbuilder.cpp

@@ -430,7 +430,7 @@ size_t VMFunctionBuilder::Emit(int opcode, int opa, int opb, int opc)
 	{
 		ParamChange(1);
 	}
-	else if (opcode == OP_CALL || opcode == OP_CALL_K)
+	else if (opcode == OP_CALL || opcode == OP_CALL_K || opcode == OP_TAIL || opcode == OP_TAIL_K)
 	{
 		ParamChange(-opb);
 	}

src/zscript/vmdisasm.cpp

@@ -44,6 +44,8 @@
 #define I24		MODE_ABCJOINT
 #define I8		MODE_AIMMZ | MODE_BUNUSED | MODE_CUNUSED
 #define __BCP	MODE_AUNUSED | MODE_BCJOINT | MODE_BCPARAM
+#define RPI8	MODE_AP | MODE_BIMMZ | MODE_CUNUSED
+#define KPI8	MODE_AKP | MODE_BIMMZ | MODE_CUNUSED
 #define RPI8I8	MODE_AP | MODE_BIMMZ | MODE_CIMMZ
 #define KPI8I8	MODE_AKP | MODE_BIMMZ | MODE_CIMMZ
 #define I8BCP	MODE_AIMMZ | MODE_BCJOINT | MODE_BCPARAM
@@ -215,9 +217,14 @@ void VMDisasm(FILE *out, const VMOP *code, int codesize, const VMScriptFunction
 			break;
 
 		case OP_CALL_K:
+		case OP_TAIL_K:
 			callfunc = (VMFunction *)func->KonstA[code[i].a].o;
 			callname = callfunc->Name != NAME_None ? callfunc->Name : "[anonfunc]";
-			col = printf_wrapper(out, "%.23s,%d,%d", callname, code[i].b, code[i].c);
+			col = printf_wrapper(out, "%.23s,%d", callname, code[i].b);
+			if (code[i].op == OP_CALL_K)
+			{
+				printf_wrapper(out, ",%d", code[i].c);
+			}
 			break;
 
 		case OP_RET:
@@ -316,13 +323,17 @@ void VMDisasm(FILE *out, const VMOP *code, int codesize, const VMScriptFunction
 		{
 			printf_wrapper(out, "%d\n", code[i].i24);
 		}
-		else if (code[i].op == OP_CALL_K)
+		else
 		{
-			printf_wrapper(out, "%d,%d,%d   [%p]\n", code[i].a, code[i].b, code[i].c, callfunc);
+			printf_wrapper(out, "%d,%d,%d", code[i].a, code[i].b, code[i].c);
+			if (code[i].op == OP_CALL_K || code[i].op == OP_TAIL_K)
+			{
+				printf_wrapper(out, "   [%p]\n", callfunc);
 			}
 			else
 			{
-			printf_wrapper(out, "%d,%d,%d\n", code[i].a, code[i].b, code[i].c);
+				printf_wrapper(out, "\n");
+			}
 		}
 	}
 }

src/zscript/vmexec.h

@@ -539,6 +539,43 @@ begin:
 			pc += C;			// Skip RESULTs
 		}
 		NEXTOP;
+	OP(TAIL_K):
+		ASSERTKA(a);
+		assert(konstatag[a] == ATAG_OBJECT);
+		ptr = konsta[a].o;
+		goto Do_TAILCALL;
+	OP(TAIL):
+		ASSERTA(a);
+		ptr = reg.a[a];
+	Do_TAILCALL:
+		assert(B <= f->NumParam);
+		assert(C <= MAX_RETURNS);
+		{
+			VMFunction *call = (VMFunction *)ptr;
+
+			if (call->Native)
+			{
+				return static_cast<VMNativeFunction *>(call)->NativeCall(stack, reg.param + f->NumParam - B, B, ret, numret);
+			}
+			else
+			{ // FIXME: Not a true tail call
+				VMScriptFunction *script = static_cast<VMScriptFunction *>(call);
+				VMFrame *newf = stack->AllocFrame(script);
+				VMFillParams(reg.param + f->NumParam - B, newf, B);
+				try
+				{
+					numret = Exec(stack, script->Code, ret, numret);
+				}
+				catch(...)
+				{
+					stack->PopFrame();
+					throw;
+				}
+				stack->PopFrame();
+				return numret;
+			}
+		}
+		NEXTOP;
 	OP(RET):
 		if (B == REGT_NIL)
 		{ // No return values

src/zscript/vmops.h

@@ -77,6 +77,8 @@ xx(PARAM,	param,	__BCP),		// push parameter encoded in BC for function call (B=r
 xx(PARAMI,	parami,	I24),		// push immediate, signed integer for function call
 xx(CALL,	call,	RPI8I8),	// Call function pkA with parameter count B and expected result count C
 xx(CALL_K,	call,	KPI8I8),
+xx(TAIL,	tail,	RPI8),		// Call+Ret in a single instruction
+xx(TAIL_K,	tail,	KPI8),
 xx(RESULT,	result,	__BCP),		// Result should go in register encoded in BC (in caller, after CALL)
 xx(RET,		ret,	I8BCP),		// Copy value from register encoded in BC to return value A, possibly returning
 xx(TRY,		try,	I24),		// When an exception is thrown, start searching for a handler at pc + ABC