From 32a7cd31da9fd3c34c8873e02a9aa8b34de6248b Mon Sep 17 00:00:00 2001
From: Irmen de Jong <irmen@razorvine.net>
Date: Tue, 15 Sep 2020 00:31:44 +0200
Subject: [PATCH] more optimal codegen for if statements

---
 .../compiler/target/c64/codegen/AsmGen.kt     | 43 ++++++++++++++-----
 docs/source/todo.rst                          |  4 +-
 examples/test.p8                              | 32 +++++++-------
 3 files changed, 50 insertions(+), 29 deletions(-)

diff --git a/compiler/src/prog8/compiler/target/c64/codegen/AsmGen.kt b/compiler/src/prog8/compiler/target/c64/codegen/AsmGen.kt
index f68e560bf..2ad774a2d 100644
--- a/compiler/src/prog8/compiler/target/c64/codegen/AsmGen.kt
+++ b/compiler/src/prog8/compiler/target/c64/codegen/AsmGen.kt
@@ -821,17 +821,38 @@ $save       .byte 0
             }
 
     private fun translate(stmt: IfStatement) {
-        // TODO don't generate needless jumps/labels when the if or else block is empty
-        expressionsAsmGen.translateExpression(stmt.condition)
-        translateTestStack(stmt.condition.inferType(program).typeOrElse(DataType.STRUCT))
-        val elseLabel = makeLabel("if_else")
-        val endLabel = makeLabel("if_end")
-        out("  beq  $elseLabel")
-        translate(stmt.truepart)
-        out("  jmp  $endLabel")
-        out(elseLabel)
-        translate(stmt.elsepart)
-        out(endLabel)
+        when {
+            stmt.elsepart.containsNoCodeNorVars() -> {
+                // empty else
+                expressionsAsmGen.translateExpression(stmt.condition)
+                translateTestStack(stmt.condition.inferType(program).typeOrElse(DataType.STRUCT))
+                val endLabel = makeLabel("if_end")
+                out("  beq  $endLabel")
+                translate(stmt.truepart)
+                out(endLabel)
+            }
+            stmt.truepart.containsNoCodeNorVars() -> {
+                // empty true part
+                expressionsAsmGen.translateExpression(stmt.condition)
+                translateTestStack(stmt.condition.inferType(program).typeOrElse(DataType.STRUCT))
+                val endLabel = makeLabel("if_end")
+                out("  bne  $endLabel")
+                translate(stmt.elsepart)
+                out(endLabel)
+            }
+            else -> {
+                expressionsAsmGen.translateExpression(stmt.condition)
+                translateTestStack(stmt.condition.inferType(program).typeOrElse(DataType.STRUCT))
+                val elseLabel = makeLabel("if_else")
+                val endLabel = makeLabel("if_end")
+                out("  beq  $elseLabel")
+                translate(stmt.truepart)
+                out("  jmp  $endLabel")
+                out(elseLabel)
+                translate(stmt.elsepart)
+                out(endLabel)
+            }
+        }
     }
 
     private fun translateTestStack(dataType: DataType) {
diff --git a/docs/source/todo.rst b/docs/source/todo.rst
index aadfe3a51..87242508c 100644
--- a/docs/source/todo.rst
+++ b/docs/source/todo.rst
@@ -2,15 +2,15 @@
 TODO
 ====
 
+- get rid of all other TODO's in the code ;-)
+- gfx examples are now a few hundred bytes larger than before. Why is that, can it be fixed?
 - compiler errors and warnings in standard format so the IDE shows them as clickable links; ./test.asm:2578:3: blablabla
 - further optimize assignment codegeneration
 - auto select correct library to import based on target, instead of having c64- and  cx16-  prefix variants
-- get rid of all TODO's ;-)
 - implement @stack for asmsub parameters
 - make it possible to use cpu opcodes such as 'nop' as variable names by prefixing all asm vars with something such as '_'
 - option to load the built-in library files from a directory instead of the embedded ones (for easier library development/debugging)
 - aliases for imported symbols for example perhaps '%alias print = c64scr.print' ?
-- 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
 
 
diff --git a/examples/test.p8 b/examples/test.p8
index e1757a1bc..72fec038d 100644
--- a/examples/test.p8
+++ b/examples/test.p8
@@ -9,23 +9,23 @@ main {
 
     sub start() {
 
-        %asm {{
-            sei
-            ldy  #0
-            sty  $1
-            lda  #0
--           sta  $f000,y
-            iny
-            bne  -
--           lda  $f000,y
-            sta  $0400,y
-            iny
-            bne  -
-        }}
+        ubyte b
+        if b > 15  {
+            b = 99
+        } else {
+            ; nothing
+        }
 
-        repeat 60000 {
-            ubyte a = sin (3)
-            a++
+        if b > 15  {
+            ; nothing
+        } else {
+            b = 99
+        }
+
+        if b > 15  {
+            ; nothing
+        } else {
+            ; nothing
         }
 
 ;asmsub  clear_screen (ubyte char @ A, ubyte color @ Y) clobbers(A)  { ...}