From 40071b14313432d7008348a871c301c281a59d15 Mon Sep 17 00:00:00 2001
From: Irmen de Jong <irmen@razorvine.net>
Date: Wed, 9 Sep 2020 21:37:56 +0200
Subject: [PATCH] fix compiler crash with adding too many typecasts to args. 
 useless lsb() and msb() are optimized away.

---
 .../prog8/ast/processing/TypecastsAdder.kt    |  1 +
 .../prog8/optimizer/ExpressionSimplifier.kt   | 43 +++++++++++++++++++
 examples/test.p8                              |  3 --
 3 files changed, 44 insertions(+), 3 deletions(-)

diff --git a/compiler/src/prog8/ast/processing/TypecastsAdder.kt b/compiler/src/prog8/ast/processing/TypecastsAdder.kt
index 4641cacd1..1c4c1136a 100644
--- a/compiler/src/prog8/ast/processing/TypecastsAdder.kt
+++ b/compiler/src/prog8/ast/processing/TypecastsAdder.kt
@@ -139,6 +139,7 @@ class TypecastsAdder(val program: Program, val errors: ErrorReporter) : AstWalke
                                         call.args[arg.second.index],
                                         TypecastExpression(arg.second.value, possibleType, true, arg.second.value.position),
                                         call as Node)
+                                break
                             }
                         }
                     }
diff --git a/compiler/src/prog8/optimizer/ExpressionSimplifier.kt b/compiler/src/prog8/optimizer/ExpressionSimplifier.kt
index bbe7a03cf..ba971d7c9 100644
--- a/compiler/src/prog8/optimizer/ExpressionSimplifier.kt
+++ b/compiler/src/prog8/optimizer/ExpressionSimplifier.kt
@@ -297,6 +297,49 @@ internal class ExpressionSimplifier(private val program: Program) : AstWalker()
         return noModifications
     }
 
+    override fun after(functionCall: FunctionCall, parent: Node): Iterable<IAstModification> {
+        if(functionCall.target.nameInSource == listOf("lsb")) {
+            val arg = functionCall.args[0]
+            if(arg is TypecastExpression) {
+                val valueDt = arg.expression.inferType(program)
+                if (valueDt.istype(DataType.BYTE) || valueDt.istype(DataType.UBYTE)) {
+                    // useless lsb() of byte value that was casted to word
+                    return listOf(IAstModification.ReplaceNode(functionCall, arg.expression, parent))
+                }
+            } else {
+                val argDt = arg.inferType(program)
+                if (argDt.istype(DataType.BYTE) || argDt.istype(DataType.UBYTE)) {
+                    // useless lsb() of byte value
+                    return listOf(IAstModification.ReplaceNode(functionCall, arg, parent))
+                }
+            }
+        }
+        else if(functionCall.target.nameInSource == listOf("msb")) {
+            val arg = functionCall.args[0]
+            if(arg is TypecastExpression) {
+                val valueDt = arg.expression.inferType(program)
+                if (valueDt.istype(DataType.BYTE) || valueDt.istype(DataType.UBYTE)) {
+                    // useless msb() of byte value that was casted to word, replace with 0
+                    return listOf(IAstModification.ReplaceNode(
+                            functionCall,
+                            NumericLiteralValue(valueDt.typeOrElse(DataType.UBYTE), 0, arg.expression.position),
+                            parent))
+                }
+            } else {
+                val argDt = arg.inferType(program)
+                if (argDt.istype(DataType.BYTE) || argDt.istype(DataType.UBYTE)) {
+                    // useless msb() of byte value, replace with 0
+                    return listOf(IAstModification.ReplaceNode(
+                            functionCall,
+                            NumericLiteralValue(argDt.typeOrElse(DataType.UBYTE), 0, arg.position),
+                            parent))
+                }
+            }
+        }
+
+        return noModifications
+    }
+
     private fun determineY(x: Expression, subBinExpr: BinaryExpression): Expression? {
         return when {
             subBinExpr.left isSameAs x -> subBinExpr.right
diff --git a/examples/test.p8 b/examples/test.p8
index 7f53bfdfc..fb53ce240 100644
--- a/examples/test.p8
+++ b/examples/test.p8
@@ -11,9 +11,6 @@ main {
 
         c64.CHROUT('*')
 
-        uword value = lsb(rnd() & 31)   ; TODO fix compiler crash
-
-
 ;asmsub  clear_screen (ubyte char @ A, ubyte color @ Y) clobbers(A)  { ...}
 ; TODO dont cause name conflict if we define sub or sub with param 'color' or even a var 'color' later.