From 4d840c7db854fe5b30e545239286a88552317fbd Mon Sep 17 00:00:00 2001
From: Irmen de Jong <irmen@razorvine.net>
Date: Thu, 11 Aug 2022 22:51:09 +0200
Subject: [PATCH] optimized mkword(0, X)

---
 .../src/prog8/optimizer/ExpressionSimplifier.kt  |  8 ++++++++
 docs/source/todo.rst                             |  2 --
 examples/test.p8                                 | 16 ++++++++--------
 3 files changed, 16 insertions(+), 10 deletions(-)

diff --git a/codeOptimizers/src/prog8/optimizer/ExpressionSimplifier.kt b/codeOptimizers/src/prog8/optimizer/ExpressionSimplifier.kt
index 0390cc691..6dcbded5d 100644
--- a/codeOptimizers/src/prog8/optimizer/ExpressionSimplifier.kt
+++ b/codeOptimizers/src/prog8/optimizer/ExpressionSimplifier.kt
@@ -331,6 +331,14 @@ class ExpressionSimplifier(private val program: Program) : AstWalker() {
             }
         }
 
+        if(functionCallExpr.target.nameInSource == listOf("mkword")) {
+            if(functionCallExpr.args[0].constValue(program)?.number==0.0) {
+                // just cast the lsb to uword
+                val cast = TypecastExpression(functionCallExpr.args[1], DataType.UWORD, true, functionCallExpr.position)
+                return listOf(IAstModification.ReplaceNode(functionCallExpr, cast, parent))
+            }
+        }
+
         return noModifications
     }
 
diff --git a/docs/source/todo.rst b/docs/source/todo.rst
index 0f9cd2502..ffee1d3bf 100644
--- a/docs/source/todo.rst
+++ b/docs/source/todo.rst
@@ -4,8 +4,6 @@ TODO
 For next release
 ^^^^^^^^^^^^^^^^
 - crc ^= mkword(@(data), 0)  produces faulty asm,   as opposed to crc ^= mkword(variable, 0)
-- optimize asm generated for mkword(0, X) and mkword(X, 0)
-- check signed value >> and << .... do we calculate the right thing?
 
 ...
 
diff --git a/examples/test.p8 b/examples/test.p8
index e86b65809..8edc1dc61 100644
--- a/examples/test.p8
+++ b/examples/test.p8
@@ -3,17 +3,17 @@
 
 main {
     sub start() {
-        uword ww = $ff34
-        ww = ww ^ ww<<8
+        ubyte left = $12
+        ubyte right = $34
+        uword ww
+
+        ww = mkword(left, right)
         txt.print_uwhex(ww, true)
-        ww = $ff34
-        ww = ww ^ mkword(lsb(ww), 0)
+        ww = mkword(left, 0)
         txt.print_uwhex(ww, true)
-        ww = $ff34
-        ww  = ww ^ ww >> 8
+        ww = mkword(0, right)
         txt.print_uwhex(ww, true)
-        ww = $ff34
-        ww  = ww ^ msb(ww)
+        ww = right as uword
         txt.print_uwhex(ww, true)
     }