fix warnings about unreachable code

compiler/src/prog8/ast/processing/AstChecker.kt

@@ -1054,16 +1054,18 @@ internal class AstChecker(private val program: Program,
 
     private fun visitStatements(statements: List<Statement>) {
         for((index, stmt) in statements.withIndex()) {
-            if(stmt is FunctionCallStatement
+            if(index < statements.lastIndex && statements[index+1] !is Subroutine) {
-                    && stmt.target.nameInSource.last()=="exit"
+                when {
-                    && index < statements.lastIndex) {
+                    stmt is FunctionCallStatement && stmt.target.nameInSource.last() == "exit" -> {
-                println("STMT AFTER EXIT ${statements[index+1]}") // TODO fix message if next stmt is not a regular stmt
+                        errors.warn("unreachable code, preceding exit call will never return", statements[index + 1].position)
-                errors.warn("unreachable code, preceding exit call will never return", statements[index + 1].position)
+                    }
-            }
+                    stmt is Return && statements[index + 1] !is Subroutine -> {
-
+                        errors.warn("unreachable code, preceding return statement", statements[index + 1].position)
-            if(stmt is Return && index < statements.lastIndex) {
+                    }
-                println("STMT AFTER RETURN ${statements[index+1]}") // TODO fix message if next stmt is not a regular stmt
+                    stmt is Jump && statements[index + 1] !is Subroutine -> {
-                errors.warn("unreachable code, preceding return statement", statements[index + 1].position)
+                        errors.warn("unreachable code, preceding jump statement", statements[index + 1].position)
+                    }
+                }
             }
 
             stmt.accept(this)

compiler/src/prog8/compiler/Main.kt

@@ -40,7 +40,6 @@ fun compileProgram(filepath: Path,
             if (optimize)
                 optimizeAst(programAst, errors)
             postprocessAst(programAst, errors, compilationOptions)
-            printAst(programAst) // TODO
             if(writeAssembly)
                 programName = writeAssembly(programAst, errors, outputDir, optimize, compilationOptions)
         }

docs/source/index.rst

@@ -135,31 +135,29 @@ Design principles and features
 
 - It is a cross-compiler running on modern machines (Linux, MacOS, Windows, ...)
   The generated output is a machine code program runnable on actual 8-bit 6502 hardware.
-- Usable on most operating systems.
+- Based on simple and familiar imperative structured programming (it looks like a mix of C and Python)
-- Based on simple and familiar imperative structured programming paradigm.
+- 'One statement per line' code, resulting in clear readable programs.
-- 'One statement per line' code style, resulting in clear readable programs.
 - Modular programming and scoping via modules, code blocks, and subroutines.
-- Provide high level programming constructs but stay close to the metal;
+- Provide high level programming constructs but at the same time stay close to the metal;
   still able to directly use memory addresses, CPU registers and ROM subroutines,
   and inline assembly to have full control when every cycle or byte matters
-- Arbitrary number of subroutine parameters (constrained only by available memory)
+- Arbitrary number of subroutine parameters
-- Nested subroutines can access variables from outer scopes, this avoids the need and overhead to pass everything via parameters
 - Complex nested expressions are possible
-- Values are typed. Types supported include signed and unsigned bytes and words, arrays, strings and floats.
+- Nested subroutines can access variables from outer scopes to avoids the overhead to pass everything via parameters
+- Values are typed. Available data types include signed and unsigned bytes and words, arrays, strings and floats.
 - No dynamic memory allocation or sizing! All variables stay fixed size as determined at compile time.
 - Provide various quality of life language features and library subroutines specifically for the target platform.
 - Provide a very convenient edit/compile/run cycle by being able to directly launch
-  the compiled program in an emulator and provide debugging information to the emulator.
+  the compiled program in an emulator and provide debugging information to this emulator.
-- The compiler outputs a regular 6502 assembly source code file, but doesn't assemble this itself.
-  The (separate) '64tass' cross-assembler tool is used for that.
 - Arbitrary control flow jumps and branches are possible,
   and will usually translate directly into the appropriate single 6502 jump/branch instruction.
 - There are no complicated built-in error handling or overflow checks, you'll have to take care
   of this yourself if required. This keeps the language and code simple and efficient.
-- The compiler tries to optimize the program and generated code, but hand-tuning of the
+- The compiler tries to optimize the program and generated code a bit, but hand-tuning of the
   performance or space-critical parts will likely still be required. This is supported by
   the ability to easily write embedded assembly code directly in the program source code.
 - There are many built-in functions, such as ``sin``, ``cos``, ``rnd``, ``abs``, ``min``, ``max``, ``sqrt``, ``msb``, ``rol``, ``ror``, ``swap``, ``memset``, ``memcopy``, ``sort`` and ``reverse``
+- Assembling the generated code into a program wil be done by an external cross-assembler tool.
 
 
 .. _requirements:

docs/source/todo.rst

@@ -3,19 +3,14 @@ TODO
 ====
 
 - implement the asm for bitshift on arrays (last missing assembly code generation)
-- remove statements after an exit() or return
-- fix warnings about that unreachable code?
 
-- add a compiler option to not include variable initialization code (useful if the program is expected to run only once, such as a game)
+- add a routine to plot a single bitmap pixel
-  the program will then rely solely on the  values as they are in memory at the time of program startup.
+- create real assembly routines for the bresenham line and circle and disc code in bitmap gfx
-
+- also add assembly routines for drawing rectangles (filled/open) in bitmap gfx
-- create real assembly routines for the bresenham line and circle code
+- add a turtle example once we have such highres drawing routines
-- also add assembly routines in c64scr for drawing rectangles (filled/open)
-- add these routines for bitmap screen modes as well
-- add a turtle example once we have highres drawing routines
 
 - aliases for imported symbols for example perhaps '%alias print = c64scr.print'
-- option to load library files from a directory instead of the embedded ones
+- option to load library files from a directory instead of the embedded ones (easier library development/debugging)
 
 
 
@@ -42,12 +37,14 @@ More optimizations
 
 Add more compiler optimizations to the existing ones.
 
-- on the language AST level
+- remove unreachable code after an exit(), return or goto
-- on the final assembly source level
+- working subroutine inlining (start with trivial routines, grow to taking care of vars and identifier refs to them)
+- add a compiler option to not include variable initialization code (useful if the program is expected to run only once, such as a game)
+  the program will then rely solely on the values as they are in memory at the time of program startup.
+- Also some library routines and code patterns could perhaps be optimized further
 - can the parameter passing to subroutines be optimized to avoid copying?
-- working subroutine inlining (taking care of vars and identifier refs to them)
+- more optimizations on the language AST level
-
+- more optimizations on the final assembly source level
-Also some library routines and code patterns could perhaps be optimized further
 
 
 Eval stack redesign? (lot of work)
@@ -59,13 +56,14 @@ It could then even be moved into the zeropage to greatly reduce code size and sl
 
 Or just move the LSB portion into a slab of the zeropage.
 
-Allocate a fixed word in ZP that is the TOS so we can always operate on TOS directly
+Allocate a fixed word in ZP that is the Top Of Stack value so we can always operate on TOS directly
-without having to to index into the stack?
+without having to index with X into the eval stack all the time?
+This could GREATLY improvde code size and speed for operatios that work on just a single value.
 
 
-Bugs
+Bug Fixing
-^^^^
+^^^^^^^^^^
-Ofcourse there are still bugs to fix ;)
+Ofcourse there are always bugs to fix ;)
 
 
 Misc

examples/test.p8

@@ -12,16 +12,19 @@ main {
         bla()
         exit(4)
         v1 = 100
+        goto start          ; TODO unreachable code warning
         v2 = 127
         A=5
+        return
 
         sub bla () {
             A=99
             bla2()
-
+            exit(99)
 
             sub bla2 () {
                 A=100
+                return
                 foo.ding()
                 foo.ding2()
             }