Fix division edge cases.

Author: AsynchronousAI

compiler/ir.go

@@ -191,8 +191,11 @@ var inlineHelpers = map[string]inlineHelper{
 			fmt.Sprintf("local %s = %s", aVar, args[0]),
 			fmt.Sprintf("local %s = %s", bVar, args[1]),
 			fmt.Sprintf("local %s", target),
-			fmt.Sprintf("if %s == 0 then error(\"division by zero\") end", bVar),
-			fmt.Sprintf("if %s >= 0 then", aVar),
+			fmt.Sprintf("if %s == 0 then", bVar),
+			fmt.Sprintf("\t%s = -1", target),
+			fmt.Sprintf("elseif %s == -1 and %s == -2147483648 then", bVar, aVar),
+			fmt.Sprintf("\t%s = -2147483648", target),
+			fmt.Sprintf("elseif %s >= 0 then", aVar),
 			fmt.Sprintf("\t%s = (%s - (%s %% %s)) // %s", target, aVar, aVar, bVar, bVar),
 			"else",
 			fmt.Sprintf("\t%s = -((-%s) - ((-%s) %% %s)) // %s", target, aVar, aVar, bVar, bVar),

compiler/math.go

@@ -35,10 +35,16 @@ func rem(w *OutputWriter, command AssemblyCommand) { /* rem & remu instructions
 	dst := irArgExpr(w, command.Arguments[0])
 	lhs := irArgExpr(w, command.Arguments[1])
 	rhs := irArgExpr(w, command.Arguments[2])
+
+	// RISC-V: division by zero: rem(a, 0) = a
 	if command.Name == "remu" {
-		Emit(w, IRStmtAssign(dst, irU32(w, IRBinop("%", irU32(w, lhs), irU32(w, rhs)))))
+		u_lhs := irU32(w, lhs)
+		u_rhs := irU32(w, rhs)
+		Emit(w, IRStmtAssign(dst, IRIfExpr(IRBinop("==", u_rhs, IRLit(0)), u_lhs, irU32(w, IRBinop("%", u_lhs, u_rhs)))))
 	} else {
-		Emit(w, IRStmtAssign(dst, irI32(w, IRBinop("%", irI32(w, lhs), irI32(w, rhs)))))
+		i_lhs := irI32(w, lhs)
+		i_rhs := irI32(w, rhs)
+		Emit(w, IRStmtAssign(dst, IRIfExpr(IRBinop("==", i_rhs, IRLit(0)), i_lhs, irI32(w, IRBinop("%", i_lhs, i_rhs)))))
 	}
 }
 func neg(w *OutputWriter, command AssemblyCommand) { /* neg & negi instructions */
@@ -47,13 +53,24 @@ func neg(w *OutputWriter, command AssemblyCommand) { /* neg & negi instructions
 	Emit(w, IRStmtAssign(dst, irI32(w, IRUnop("-", irI32(w, src)))))
 }
 
-/** mulh — high 32 bits of 64-bit product */
 func mulh(w *OutputWriter, command AssemblyCommand) {
 	dst := irArgExpr(w, command.Arguments[0])
 	lhs := irArgExpr(w, command.Arguments[1])
 	rhs := irArgExpr(w, command.Arguments[2])
-	Emit(w, IRStmtAssign(dst,
-		IRCall(BIT32_BAND,
-			IRCall(BIT32_LSHIFT, lhs, rhs),
-			IRLitHex(0xFFFFFFFF))))
+
+	// Use math.floor( (a * b) / 2^32 ) for mulh
+	// We use u32 for all operands to ensure we stay in the realm of Luau's 53-bit mantissa correctly if possible, 
+	// but for full 64-bit mul we might need care.
+	// RISC-V mulhu/mulh/mulhsu have different sign handling.
+	
+	if command.Name == "mulhu" {
+		u_lhs := irU32(w, lhs)
+		u_rhs := irU32(w, rhs)
+		Emit(w, IRStmtAssign(dst, irU32(w, IRCall(MATH_FLOOR, IRBinop("/", IRBinop("*", u_lhs, u_rhs), IRLit(0x100000000))))))
+	} else {
+		// mulh (signed)
+		i_lhs := irI32(w, lhs)
+		i_rhs := irI32(w, rhs)
+		Emit(w, IRStmtAssign(dst, irI32(w, IRCall(MATH_FLOOR, IRBinop("/", IRBinop("*", i_lhs, i_rhs), IRLit(0x100000000))))))
+	}
 }