From 31491c62c5785feab57cf206c44a5ca4c805d61e Mon Sep 17 00:00:00 2001
From: Irmen de Jong <irmen@razorvine.net>
Date: Sat, 20 Nov 2021 22:33:13 +0100
Subject: [PATCH] add some more const folding patterns

---
 .../optimizer/ConstantFoldingOptimizer.kt     | 34 ++++++++++++++++-
 examples/test.p8                              | 38 ++++++++-----------
 2 files changed, 47 insertions(+), 25 deletions(-)

diff --git a/codeOptimizers/src/prog8/optimizer/ConstantFoldingOptimizer.kt b/codeOptimizers/src/prog8/optimizer/ConstantFoldingOptimizer.kt
index 16c06bb25..ca24b08eb 100644
--- a/codeOptimizers/src/prog8/optimizer/ConstantFoldingOptimizer.kt
+++ b/codeOptimizers/src/prog8/optimizer/ConstantFoldingOptimizer.kt
@@ -79,7 +79,7 @@ class ConstantFoldingOptimizer(private val program: Program) : AstWalker() {
         return noModifications
     }
 
-    /**
+    /*
      * Try to constfold a binary expression.
      * Compile-time constant sub expressions will be evaluated on the spot.
      * For instance, "9 * (4 + 2)" will be optimized into the integer literal 54.
@@ -186,13 +186,43 @@ class ConstantFoldingOptimizer(private val program: Program) : AstWalker() {
             }
         }
 
+        val evaluator = ConstExprEvaluator()
+
         // const fold when both operands are a const
         if(leftconst != null && rightconst != null) {
-            val evaluator = ConstExprEvaluator()
             val result = evaluator.evaluate(leftconst, expr.operator, rightconst)
             modifications += IAstModification.ReplaceNode(expr, result, parent)
         }
 
+
+        val leftBinExpr = expr.left as? BinaryExpression
+        val rightBinExpr = expr.right as? BinaryExpression
+        if(expr.operator=="+" || expr.operator=="-") {
+            if(leftBinExpr!=null && rightBinExpr!=null) {
+                val c1 = leftBinExpr.right.constValue(program)
+                val c2 = rightBinExpr.right.constValue(program)
+                if(leftBinExpr.operator=="+" && rightBinExpr.operator=="+") {
+                    if (c1 != null && c2 != null) {
+                        // (X + C1) <plusmin> (Y + C2)  =>  (X <plusmin> Y) + (C1 <plusmin> C2)
+                        val c3 = evaluator.evaluate(c1, expr.operator, c2)
+                        val xwithy = BinaryExpression(leftBinExpr.left, expr.operator, rightBinExpr.left, expr.position)
+                        val newExpr = BinaryExpression(xwithy, "+", c3, expr.position)
+                        modifications += IAstModification.ReplaceNode(expr, newExpr, parent)
+                    }
+                }
+                else if(leftBinExpr.operator=="*" && rightBinExpr.operator=="*"){
+                    if (c1 != null && c2 != null && c1==c2) {
+                        //(X * C) <plusmin> (Y * C)  =>  (X <plusmin> Y) * C
+                        val xwithy = BinaryExpression(leftBinExpr.left, expr.operator, rightBinExpr.left, expr.position)
+                        val newExpr = BinaryExpression(xwithy, "*", c1, expr.position)
+                        modifications += IAstModification.ReplaceNode(expr, newExpr, parent)
+                    }
+                }
+            }
+        }
+
+
+
         return modifications
     }
 
diff --git a/examples/test.p8 b/examples/test.p8
index dd764f0d2..8730b07b9 100644
--- a/examples/test.p8
+++ b/examples/test.p8
@@ -6,19 +6,11 @@ main {
 
         ubyte xx = 1
         ubyte yy = 2
+        byte b1
+        byte b2
 
 ;; TODO add these constant folders:
-;
-;; (X + C1) + (Y + C2)  =>  (X + Y) + (C1 + C2)
-;; (X + C1) - (Y + C2)  =>  (X - Y) + (C1 - C2)
-;; ---> together:   (X + C1) <plusmin> (Y + C2)  =>  (X <plusmin> Y) + (C1 <plusmin> C2)
-
-;; (X * C) + (Y * C)  =>  (X + Y) * C
-;; (X * C) - (Y * C)  =>  (X - Y) * C
-;; ---> together:   (X * C) <plusmin> (Y * C)  =>  (X <plusmin> Y) * C
-
-;
-;; (X - C1) + (Y - C2)  =>  (X + Y) - (C1 + C2)
+;; (X - C1) <plusmin> (Y - C2)  =>  (X <plusmin> Y) - (C1 <plusmin> C2)
 ;; (X - C1) - (Y - C2)  =>  (X - Y) - (C1 - C2)
 ;
 
@@ -43,22 +35,22 @@ main {
         txt.print_ub(yy)        ; 40
         txt.nl()
 
-        xx=100
-        yy=8
-        yy = (xx+5)-(yy+10)
-        txt.print_ub(yy)        ; 87
+        b1=100
+        b2=8
+        b2 = (b1+5)-(b2+10)
+        txt.print_b(b2)        ; 87
         txt.nl()
 
-        xx=50
-        yy=40
-        yy = (xx-5)+(yy-10)
-        txt.print_ub(yy)        ; 75
+        b1=50
+        b2=40
+        b2 = (b1-5)+(b2-10)
+        txt.print_b(b2)        ; 75
         txt.nl()
 
-        xx=50
-        yy=20
-        yy = (xx-5)-(yy-10)
-        txt.print_ub(yy)        ; 35
+        b1=50
+        b2=20
+        b2 = (b1-5)-(b2-10)
+        txt.print_b(b2)        ; 35
         txt.nl()
 
         repeat {