From 107935ed31d2dd4f7ed072ad9253db8142f5527e Mon Sep 17 00:00:00 2001
From: Irmen de Jong <irmen@razorvine.net>
Date: Sat, 20 Nov 2021 22:43:08 +0100
Subject: [PATCH] add some more const folding patterns

---
 .../optimizer/ConstantFoldingOptimizer.kt     |  9 ++++
 compiler/src/prog8/compiler/Compiler.kt       |  4 +-
 docs/source/todo.rst                          |  1 -
 examples/test.p8                              | 51 -------------------
 4 files changed, 11 insertions(+), 54 deletions(-)

diff --git a/codeOptimizers/src/prog8/optimizer/ConstantFoldingOptimizer.kt b/codeOptimizers/src/prog8/optimizer/ConstantFoldingOptimizer.kt
index ca24b08eb..76ef5d137 100644
--- a/codeOptimizers/src/prog8/optimizer/ConstantFoldingOptimizer.kt
+++ b/codeOptimizers/src/prog8/optimizer/ConstantFoldingOptimizer.kt
@@ -210,6 +210,15 @@ class ConstantFoldingOptimizer(private val program: Program) : AstWalker() {
                         modifications += IAstModification.ReplaceNode(expr, newExpr, parent)
                     }
                 }
+                else 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
diff --git a/compiler/src/prog8/compiler/Compiler.kt b/compiler/src/prog8/compiler/Compiler.kt
index 5a2df381d..db9cc148d 100644
--- a/compiler/src/prog8/compiler/Compiler.kt
+++ b/compiler/src/prog8/compiler/Compiler.kt
@@ -76,7 +76,7 @@ fun compileProgram(filepath: Path,
             postprocessAst(program, errors, compilationOptions)
 
 //            println("*********** AST BEFORE ASSEMBLYGEN *************")
-//            printAst(program)
+//            printProgram(program)
 
             if (writeAssembly) {
                 val result = writeAssembly(program, errors, outputDir, quietAssembler, compilationOptions)
@@ -328,7 +328,7 @@ private fun writeAssembly(program: Program,
     errors.report()
 
 //    println("*********** AST RIGHT BEFORE ASM GENERATION *************")
-//    printAst(program)
+//    printProgram(program)
 
     compilerOptions.compTarget.machine.initializeZeropage(compilerOptions)
     val assembly = asmGeneratorFor(compilerOptions.compTarget,
diff --git a/docs/source/todo.rst b/docs/source/todo.rst
index d8f1a12ba..2ebd173b1 100644
--- a/docs/source/todo.rst
+++ b/docs/source/todo.rst
@@ -3,7 +3,6 @@ TODO
 
 For next compiler release (7.4)
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-optimize: add some more constant folders mentioned in test.p8
 optimize: there is an optimization in AsmOptimizer that can only be done correctly
  if it knows about regular ram vs io space ram distinction.
 
diff --git a/examples/test.p8 b/examples/test.p8
index 8730b07b9..ad777465f 100644
--- a/examples/test.p8
+++ b/examples/test.p8
@@ -4,56 +4,5 @@ main {
 
     sub start() {
 
-        ubyte xx = 1
-        ubyte yy = 2
-        byte b1
-        byte b2
-
-;; TODO add these constant folders:
-;; (X - C1) <plusmin> (Y - C2)  =>  (X <plusmin> Y) - (C1 <plusmin> C2)
-;; (X - C1) - (Y - C2)  =>  (X - Y) - (C1 - C2)
-;
-
-
-        ; result should be:  29  42  40  87  75  35
-
-        xx=6
-        yy=8
-        yy = (xx+5)+(yy+10)
-        txt.print_ub(yy)        ; 29
-        txt.nl()
-
-        xx=6
-        yy=8
-        yy = (xx*3)+(yy*3)
-        txt.print_ub(yy)        ; 42
-        txt.nl()
-
-        xx=13
-        yy=5
-        yy = (xx*5)-(yy*5)
-        txt.print_ub(yy)        ; 40
-        txt.nl()
-
-        b1=100
-        b2=8
-        b2 = (b1+5)-(b2+10)
-        txt.print_b(b2)        ; 87
-        txt.nl()
-
-        b1=50
-        b2=40
-        b2 = (b1-5)+(b2-10)
-        txt.print_b(b2)        ; 75
-        txt.nl()
-
-        b1=50
-        b2=20
-        b2 = (b1-5)-(b2-10)
-        txt.print_b(b2)        ; 35
-        txt.nl()
-
-        repeat {
-        }
     }
 }