todo about fixing argclobbering

docs/source/todo.rst

@@ -2,10 +2,13 @@
 TODO
 ====
 
+- BUG FIX: fix register argument clobbering when calling asmsubs. (see fixme_argclobber.p8)
+
+
 - finalize (most) of the still missing "new" assignment asm code generation
 - aliases for imported symbols for example perhaps '%alias print = c64scr.print'
 - option to load library files from a directory instead of the embedded ones (easier library development/debugging)
-- investigate support for 8bitguy's Commander X16 platform https://murray2.com/forums/commander-x16.9/  and https://github.com/commanderx16/x16-docs
+- investigate support for 8bitguy's Commander X16 platform https://www.commanderx16.com  and https://github.com/commanderx16/x16-docs
 - see if we can group some errors together for instance the (now single) errors about unidentified symbols
 
 

examples/fixme_argclobber.p8

@@ -0,0 +1,47 @@
+%import c64lib
+%import c64utils
+%import c64flt
+%zeropage basicsafe
+%option enable_floats
+
+
+; TODO: fix register argument clobbering when calling asmsubs.
+; for instance if the first arg goes into Y, and the second in A,
+; but when calculating the second argument clobbers Y, the first argument gets destroyed.
+
+main {
+
+    sub start() {
+        function(20, calculate())
+        asmfunction(20, calculate())
+
+        c64.CHROUT('\n')
+
+        if @($0400)==@($0402) and @($0401) == @($0403) {
+            c64scr.print("ok: results are same\n")
+        } else {
+            c64scr.print("error: result differ; arg got clobbered\n")
+        }
+    }
+
+    sub function(ubyte a1, ubyte a2) {
+        ; non-asm function passes via stack, this is ok
+        @($0400) = a1
+        @($0401) = a2
+    }
+
+    asmsub asmfunction(ubyte a1 @ Y, ubyte a2 @ A) {
+        ; asm-function passes via registers, risk of clobbering
+        %asm {{
+            sty  $0402
+            sta  $0403
+        }}
+    }
+
+    sub calculate() -> ubyte {
+        Y = 99
+        return Y
+    }
+}
+
+

examples/structs.p8

@@ -20,7 +20,7 @@ main {
 
         other = purple
 
-        other.red /= 3
+        other.red /= 2
         other.green = 10 + other.green / 2
         other.blue = 99
 

examples/tehtriz.p8

@@ -549,7 +549,7 @@ blocklogic {
     sub noCollision(ubyte xpos, ubyte ypos) -> ubyte {
         ubyte i
         for i in 15 downto 0 {
-            ; TODO FIX THIS when compiling without optimizations (codegen problem: clobbering register arguments):
+            ; TODO FIX THIS when compiling without optimizations (codegen problem: clobbering register arguments, see fixme_argclobber):
             if currentBlock[i] and c64scr.getchr(xpos + (i&3), ypos+i/4)!=32
                 return false
         }