From 8e26e38ecc730c956e8b714d526c61aaa659a313 Mon Sep 17 00:00:00 2001
From: Irmen de Jong <irmen@razorvine.net>
Date: Thu, 1 Apr 2021 23:30:19 +0200
Subject: [PATCH] fix RTS-issue with inlined return statement

---
 .../prog8/compiler/target/cpu6502/codegen/AsmGen.kt |  6 ++++--
 .../target/cpu6502/codegen/FunctionCallAsmGen.kt    | 13 +++++++++++--
 docs/source/todo.rst                                |  2 --
 3 files changed, 15 insertions(+), 6 deletions(-)

diff --git a/compiler/src/prog8/compiler/target/cpu6502/codegen/AsmGen.kt b/compiler/src/prog8/compiler/target/cpu6502/codegen/AsmGen.kt
index b0403a138..5ee41fdb6 100644
--- a/compiler/src/prog8/compiler/target/cpu6502/codegen/AsmGen.kt
+++ b/compiler/src/prog8/compiler/target/cpu6502/codegen/AsmGen.kt
@@ -1272,7 +1272,7 @@ $label              nop""")
         }
     }
 
-    private fun translate(ret: Return) {
+    internal fun translate(ret: Return, withRts: Boolean=true) {
         ret.value?.let { returnvalue ->
             val sub = ret.definingSubroutine()!!
             val returnType = sub.returntypes.single()
@@ -1291,7 +1291,9 @@ $label              nop""")
                 }
             }
         }
-        out("  rts")
+
+        if(withRts)
+            out("  rts")
     }
 
     private fun translate(asm: InlineAssembly) {
diff --git a/compiler/src/prog8/compiler/target/cpu6502/codegen/FunctionCallAsmGen.kt b/compiler/src/prog8/compiler/target/cpu6502/codegen/FunctionCallAsmGen.kt
index 6d98aaa23..631db8920 100644
--- a/compiler/src/prog8/compiler/target/cpu6502/codegen/FunctionCallAsmGen.kt
+++ b/compiler/src/prog8/compiler/target/cpu6502/codegen/FunctionCallAsmGen.kt
@@ -114,14 +114,23 @@ internal class FunctionCallAsmGen(private val program: Program, private val asmg
         if(!sub.inline || !asmgen.options.optimize) {
             asmgen.out("  jsr  $subName")
         } else {
-            // inline the subroutine
+            // inline the subroutine.
+            // we do this by copying the subroutine's statements at the call site.
+            // NOTE: *if* there is a return statement, it will be the only one, and the very last statement of the subroutine
+            // (this condition has been enforced by an ast check earlier)
             if(sub.containsDefinedVariables())
                 throw AssemblyError("can't inline sub with vars")
             if(!sub.isAsmSubroutine && sub.parameters.isNotEmpty())
                 throw AssemblyError("can't inline a non-asm subroutine with parameters")
             asmgen.out("  \t; inlined routine follows: ${sub.name} from ${sub.position}")
             val statements = sub.statements.filter { it !is ParameterVarDecl && it !is Directive }
-            statements.forEach { asmgen.translate(it) }
+            statements.forEach {
+                if(it is Return) {
+                    asmgen.translate(it, false)     // don't use RTS for the inlined return statement
+                } else {
+                    asmgen.translate(it)
+                }
+            }
         }
 
         // remember: dealing with the X register and/or dealing with return values is the responsibility of the caller
diff --git a/docs/source/todo.rst b/docs/source/todo.rst
index 3befcad78..2e98e58fe 100644
--- a/docs/source/todo.rst
+++ b/docs/source/todo.rst
@@ -2,8 +2,6 @@
 TODO
 ====
 
-- fix inlining issue with return statement inlined literally at call site
-
 - allow inlining of subroutines with vardecls
 - optimize several inner loops in gfx2
 - hoist all variable declarations up to the subroutine scope *before* even the constant folding takes place (to avoid undefined symbol errors when referring to a variable from another nested scope in the subroutine)