From 5a83c1b357880ba97eed8965b897310235f0c4e2 Mon Sep 17 00:00:00 2001
From: jespergravgaard <jesper@balmangravgaard.dk>
Date: Sat, 9 Mar 2019 18:37:23 +0100
Subject: [PATCH] Fixed clobber problem that can occur during PHI transitions.
 Closes #10

---
 .../kickc/passes/Pass4AssertNoCpuClobber.java |   6 +-
 .../dk/camelot64/kickc/test/TestPrograms.java |   5 +
 src/test/kc/scrollbig-clobber.kc              |  24 +
 src/test/ref/examples/scrollbig/scrollbig.asm |   6 +-
 src/test/ref/examples/scrollbig/scrollbig.log |  52 +-
 src/test/ref/examples/scrollbig/scrollbig.sym |  12 +-
 src/test/ref/scrollbig-clobber.asm            |  41 +
 src/test/ref/scrollbig-clobber.cfg            |  42 ++
 src/test/ref/scrollbig-clobber.log            | 707 ++++++++++++++++++
 src/test/ref/scrollbig-clobber.sym            |  35 +
 10 files changed, 897 insertions(+), 33 deletions(-)
 create mode 100644 src/test/kc/scrollbig-clobber.kc
 create mode 100644 src/test/ref/scrollbig-clobber.asm
 create mode 100644 src/test/ref/scrollbig-clobber.cfg
 create mode 100644 src/test/ref/scrollbig-clobber.log
 create mode 100644 src/test/ref/scrollbig-clobber.sym

diff --git a/src/main/java/dk/camelot64/kickc/passes/Pass4AssertNoCpuClobber.java b/src/main/java/dk/camelot64/kickc/passes/Pass4AssertNoCpuClobber.java
index d05125679..2e0353147 100644
--- a/src/main/java/dk/camelot64/kickc/passes/Pass4AssertNoCpuClobber.java
+++ b/src/main/java/dk/camelot64/kickc/passes/Pass4AssertNoCpuClobber.java
@@ -79,14 +79,18 @@ public class Pass4AssertNoCpuClobber extends Pass2Base {
                PhiTransitions phiTransitions = new PhiTransitions(getProgram(), statementBlock);
                PhiTransitions.PhiTransition phiTransition = phiTransitions.getTransition(phiTransitionId);
                for(PhiTransitions.PhiTransition.PhiAssignment phiAssignment : phiTransition.getAssignments()) {
-                  // IF the assignment is later than the current one
                   if(phiAssignment.getAssignmentIdx() > transitionAssignmentIdx) {
+                     // IF the assignment is later than the current one
                      RValue rValue = phiAssignment.getrValue();
                      Collection<VariableRef> alive = VariableReferenceInfos.getReferencedVars(rValue);
                      aliveVars.addAll(alive);
                      VariableRef assignedVar = phiAssignment.getVariable();
                      assignedVars.remove(assignedVar);
                      alive.remove(assignedVar);
+                  } else if(phiAssignment.getAssignmentIdx() < transitionAssignmentIdx) {
+                     // IF the assignment is before the current one
+                     VariableRef assignedVar = phiAssignment.getVariable();
+                     assignedVars.remove(assignedVar);
                   }
                }
             }
diff --git a/src/test/java/dk/camelot64/kickc/test/TestPrograms.java b/src/test/java/dk/camelot64/kickc/test/TestPrograms.java
index 0dd857ea9..5ff1c92e9 100644
--- a/src/test/java/dk/camelot64/kickc/test/TestPrograms.java
+++ b/src/test/java/dk/camelot64/kickc/test/TestPrograms.java
@@ -44,6 +44,11 @@ public class TestPrograms {
       AsmFragmentTemplateUsages.logUsages(log, false, false, false, false, false, false);
    }
 
+   @Test
+   public void testClobberProblem() throws IOException, URISyntaxException {
+      compileAndCompare("scrollbig-clobber");
+   }
+
    @Test
    public void testComparisonsSWord() throws IOException, URISyntaxException {
       compileAndCompare("test-comparisons-sword");
diff --git a/src/test/kc/scrollbig-clobber.kc b/src/test/kc/scrollbig-clobber.kc
new file mode 100644
index 000000000..878b61a23
--- /dev/null
+++ b/src/test/kc/scrollbig-clobber.kc
@@ -0,0 +1,24 @@
+// Clobber problem in next_char return value
+
+byte* TEXT = "cml @";
+
+void main() {
+    byte* SCREEN = $400;
+    for( byte i: 0..255) {
+        SCREEN[i] = next_char();
+    }
+}
+
+byte* nxt = TEXT;
+
+// Find the next char of the text
+byte next_char() {
+    byte c = *nxt;
+    if(c=='@') {
+        nxt = TEXT;
+        c = *nxt;
+    }
+    nxt++;
+    return c;
+}
+
diff --git a/src/test/ref/examples/scrollbig/scrollbig.asm b/src/test/ref/examples/scrollbig/scrollbig.asm
index 5d1e3326a..f98b67ccd 100644
--- a/src/test/ref/examples/scrollbig/scrollbig.asm
+++ b/src/test/ref/examples/scrollbig/scrollbig.asm
@@ -57,6 +57,7 @@ scroll_bit: {
     cmp #0
     bne b1
     jsr next_char
+    txa
     sta c
     lda #0
     sta c+1
@@ -143,9 +144,10 @@ scroll_hard: {
 next_char: {
     ldy #0
     lda (nxt),y
-    cmp #'@'
+    tax
+    cpx #'@'
     bne b1
-    lda TEXT
+    ldx TEXT
     lda #<TEXT
     sta nxt
     lda #>TEXT
diff --git a/src/test/ref/examples/scrollbig/scrollbig.log b/src/test/ref/examples/scrollbig/scrollbig.log
index ea0cc8dcb..f258c9217 100644
--- a/src/test/ref/examples/scrollbig/scrollbig.log
+++ b/src/test/ref/examples/scrollbig/scrollbig.log
@@ -2104,13 +2104,13 @@ Limited combination testing to 100 combinations of 512 possible.
 Uplifting [scroll_hard] best 24938 combination reg byte x [ scroll_hard::i#2 scroll_hard::i#1 ] 
 Uplifting [] best 24626 combination zp ZP_WORD:4 [ current_chargen#27 current_chargen#11 current_chargen#19 current_chargen#5 ] zp ZP_BYTE:3 [ current_bit#29 current_bit#12 current_bit#21 current_bit#5 ] zp ZP_WORD:11 [ nxt#18 nxt#31 nxt#14 nxt#36 nxt#19 ] reg byte x [ scroll#18 scroll#10 scroll#3 ] 
 Uplifting [fillscreen] best 24626 combination zp ZP_WORD:14 [ fillscreen::cursor#2 fillscreen::cursor#1 ] 
-Uplifting [next_char] best 24608 combination reg byte a [ next_char::return#1 next_char::c#0 next_char::c#1 ] reg byte a [ next_char::return#0 ] 
-Uplifting [main] best 24608 combination 
-Uplifting [scroll_soft] best 24608 combination 
+Uplifting [next_char] best 24610 combination reg byte x [ next_char::return#1 next_char::c#0 next_char::c#1 ] reg byte x [ next_char::return#0 ] 
+Uplifting [main] best 24610 combination 
+Uplifting [scroll_soft] best 24610 combination 
 Attempting to uplift remaining variables inzp ZP_BYTE:3 [ current_bit#29 current_bit#12 current_bit#21 current_bit#5 ]
-Uplifting [] best 24608 combination zp ZP_BYTE:3 [ current_bit#29 current_bit#12 current_bit#21 current_bit#5 ] 
+Uplifting [] best 24610 combination zp ZP_BYTE:3 [ current_bit#29 current_bit#12 current_bit#21 current_bit#5 ] 
 Attempting to uplift remaining variables inzp ZP_BYTE:17 [ scroll_bit::$3 ]
-Uplifting [scroll_bit] best 24602 combination reg byte a [ scroll_bit::$3 ] 
+Uplifting [scroll_bit] best 24606 combination reg byte a [ scroll_bit::$3 ] 
 Coalescing zero page register with common assignment [ zp ZP_WORD:4 [ current_chargen#27 current_chargen#11 current_chargen#19 current_chargen#5 ] ] with [ zp ZP_WORD:20 [ scroll_bit::$4 ] ] - score: 1
 Coalescing zero page register with common assignment [ zp ZP_WORD:4 [ current_chargen#27 current_chargen#11 current_chargen#19 current_chargen#5 scroll_bit::$4 ] ] with [ zp ZP_WORD:18 [ scroll_bit::c#0 ] ] - score: 1
 Coalescing zero page register [ zp ZP_WORD:4 [ current_chargen#27 current_chargen#11 current_chargen#19 current_chargen#5 scroll_bit::$4 scroll_bit::c#0 ] ] with [ zp ZP_WORD:14 [ fillscreen::cursor#2 fillscreen::cursor#1 ] ]
@@ -2274,7 +2274,8 @@ scroll_bit: {
     jmp b8
   //SEG60 scroll_bit::@8
   b8:
-  //SEG61 [24] (byte~) scroll_bit::$3 ← (byte) next_char::return#0
+  //SEG61 [24] (byte~) scroll_bit::$3 ← (byte) next_char::return#0 -- vbuaa=vbuxx 
+    txa
   //SEG62 [25] (word) scroll_bit::c#0 ← ((word)) (byte~) scroll_bit::$3 -- vwuz1=_word_vbuaa 
     sta c
     lda #0
@@ -2447,17 +2448,18 @@ scroll_hard: {
 //SEG123 next_char
 // Find the next char of the scroll text
 next_char: {
-  //SEG124 [58] (byte) next_char::c#0 ← *((byte*) nxt#31) -- vbuaa=_deref_pbuz1 
+  //SEG124 [58] (byte) next_char::c#0 ← *((byte*) nxt#31) -- vbuxx=_deref_pbuz1 
     ldy #0
     lda (nxt),y
-  //SEG125 [59] if((byte) next_char::c#0!=(byte) '@') goto next_char::@1 -- vbuaa_neq_vbuc1_then_la1 
-    cmp #'@'
+    tax
+  //SEG125 [59] if((byte) next_char::c#0!=(byte) '@') goto next_char::@1 -- vbuxx_neq_vbuc1_then_la1 
+    cpx #'@'
     bne b1_from_next_char
     jmp b2
   //SEG126 next_char::@2
   b2:
-  //SEG127 [60] (byte) next_char::c#1 ← *((const byte*) TEXT#0) -- vbuaa=_deref_pbuc1 
-    lda TEXT
+  //SEG127 [60] (byte) next_char::c#1 ← *((const byte*) TEXT#0) -- vbuxx=_deref_pbuc1 
+    ldx TEXT
   //SEG128 [61] phi from next_char::@2 to next_char::@1 [phi:next_char::@2->next_char::@1]
   b1_from_b2:
   //SEG129 [61] phi (byte) next_char::return#1 = (byte) next_char::c#1 [phi:next_char::@2->next_char::@1#0] -- register_copy 
@@ -2670,11 +2672,11 @@ FINAL SYMBOL TABLE
 (label) next_char::@2
 (label) next_char::@return
 (byte) next_char::c
-(byte) next_char::c#0 reg byte a 3.0
-(byte) next_char::c#1 reg byte a 4.0
+(byte) next_char::c#0 reg byte x 3.0
+(byte) next_char::c#1 reg byte x 4.0
 (byte) next_char::return
-(byte) next_char::return#0 reg byte a 4.0
-(byte) next_char::return#1 reg byte a 1.5
+(byte) next_char::return#0 reg byte x 4.0
+(byte) next_char::return#1 reg byte x 1.5
 (byte*) nxt
 (byte*) nxt#14 nxt zp ZP_WORD:7 3.0
 (byte*) nxt#18 nxt zp ZP_WORD:7 4.0
@@ -2729,15 +2731,15 @@ zp ZP_WORD:5 [ scroll_bit::sc#2 scroll_bit::sc#1 ]
 reg byte a [ scroll_bit::b#2 ]
 reg byte x [ scroll_hard::i#2 scroll_hard::i#1 ]
 zp ZP_WORD:7 [ nxt#18 nxt#31 nxt#14 nxt#36 nxt#19 ]
-reg byte a [ next_char::return#1 next_char::c#0 next_char::c#1 ]
-reg byte a [ next_char::return#0 ]
+reg byte x [ next_char::return#1 next_char::c#0 next_char::c#1 ]
+reg byte x [ next_char::return#0 ]
 reg byte a [ scroll_bit::$3 ]
 reg byte a [ scroll_bit::bits#0 ]
 reg byte a [ scroll_bit::$9 ]
 
 
 FINAL ASSEMBLER
-Score: 20822
+Score: 20826
 
 //SEG0 File Comments
 // An 8x8 char letter scroller
@@ -2859,7 +2861,8 @@ scroll_bit: {
     jsr next_char
   //SEG59 [23] (byte) next_char::return#0 ← (byte) next_char::return#1
   //SEG60 scroll_bit::@8
-  //SEG61 [24] (byte~) scroll_bit::$3 ← (byte) next_char::return#0
+  //SEG61 [24] (byte~) scroll_bit::$3 ← (byte) next_char::return#0 -- vbuaa=vbuxx 
+    txa
   //SEG62 [25] (word) scroll_bit::c#0 ← ((word)) (byte~) scroll_bit::$3 -- vwuz1=_word_vbuaa 
     sta c
     lda #0
@@ -3006,15 +3009,16 @@ scroll_hard: {
 //SEG123 next_char
 // Find the next char of the scroll text
 next_char: {
-  //SEG124 [58] (byte) next_char::c#0 ← *((byte*) nxt#31) -- vbuaa=_deref_pbuz1 
+  //SEG124 [58] (byte) next_char::c#0 ← *((byte*) nxt#31) -- vbuxx=_deref_pbuz1 
     ldy #0
     lda (nxt),y
-  //SEG125 [59] if((byte) next_char::c#0!=(byte) '@') goto next_char::@1 -- vbuaa_neq_vbuc1_then_la1 
-    cmp #'@'
+    tax
+  //SEG125 [59] if((byte) next_char::c#0!=(byte) '@') goto next_char::@1 -- vbuxx_neq_vbuc1_then_la1 
+    cpx #'@'
     bne b1
   //SEG126 next_char::@2
-  //SEG127 [60] (byte) next_char::c#1 ← *((const byte*) TEXT#0) -- vbuaa=_deref_pbuc1 
-    lda TEXT
+  //SEG127 [60] (byte) next_char::c#1 ← *((const byte*) TEXT#0) -- vbuxx=_deref_pbuc1 
+    ldx TEXT
   //SEG128 [61] phi from next_char::@2 to next_char::@1 [phi:next_char::@2->next_char::@1]
   //SEG129 [61] phi (byte) next_char::return#1 = (byte) next_char::c#1 [phi:next_char::@2->next_char::@1#0] -- register_copy 
   //SEG130 [61] phi (byte*) nxt#18 = (const byte*) TEXT#0 [phi:next_char::@2->next_char::@1#1] -- pbuz1=pbuc1 
diff --git a/src/test/ref/examples/scrollbig/scrollbig.sym b/src/test/ref/examples/scrollbig/scrollbig.sym
index 0f106de57..501c86b1f 100644
--- a/src/test/ref/examples/scrollbig/scrollbig.sym
+++ b/src/test/ref/examples/scrollbig/scrollbig.sym
@@ -44,11 +44,11 @@
 (label) next_char::@2
 (label) next_char::@return
 (byte) next_char::c
-(byte) next_char::c#0 reg byte a 3.0
-(byte) next_char::c#1 reg byte a 4.0
+(byte) next_char::c#0 reg byte x 3.0
+(byte) next_char::c#1 reg byte x 4.0
 (byte) next_char::return
-(byte) next_char::return#0 reg byte a 4.0
-(byte) next_char::return#1 reg byte a 1.5
+(byte) next_char::return#0 reg byte x 4.0
+(byte) next_char::return#1 reg byte x 1.5
 (byte*) nxt
 (byte*) nxt#14 nxt zp ZP_WORD:7 3.0
 (byte*) nxt#18 nxt zp ZP_WORD:7 4.0
@@ -103,8 +103,8 @@ zp ZP_WORD:5 [ scroll_bit::sc#2 scroll_bit::sc#1 ]
 reg byte a [ scroll_bit::b#2 ]
 reg byte x [ scroll_hard::i#2 scroll_hard::i#1 ]
 zp ZP_WORD:7 [ nxt#18 nxt#31 nxt#14 nxt#36 nxt#19 ]
-reg byte a [ next_char::return#1 next_char::c#0 next_char::c#1 ]
-reg byte a [ next_char::return#0 ]
+reg byte x [ next_char::return#1 next_char::c#0 next_char::c#1 ]
+reg byte x [ next_char::return#0 ]
 reg byte a [ scroll_bit::$3 ]
 reg byte a [ scroll_bit::bits#0 ]
 reg byte a [ scroll_bit::$9 ]
diff --git a/src/test/ref/scrollbig-clobber.asm b/src/test/ref/scrollbig-clobber.asm
new file mode 100644
index 000000000..30d29f41e
--- /dev/null
+++ b/src/test/ref/scrollbig-clobber.asm
@@ -0,0 +1,41 @@
+// Clobber problem in next_char return value
+.pc = $801 "Basic"
+:BasicUpstart(main)
+.pc = $80d "Program"
+  .label nxt = 2
+main: {
+    .label SCREEN = $400
+    ldx #0
+    lda #<TEXT
+    sta nxt
+    lda #>TEXT
+    sta nxt+1
+  b1:
+    jsr next_char
+    tya
+    sta SCREEN,x
+    inx
+    cpx #0
+    bne b1
+    rts
+}
+// Find the next char of the text
+next_char: {
+    ldy #0
+    lda (nxt),y
+    tay
+    cpy #'@'
+    bne b1
+    ldy TEXT
+    lda #<TEXT
+    sta nxt
+    lda #>TEXT
+    sta nxt+1
+  b1:
+    inc nxt
+    bne !+
+    inc nxt+1
+  !:
+    rts
+}
+  TEXT: .text "cml @"
diff --git a/src/test/ref/scrollbig-clobber.cfg b/src/test/ref/scrollbig-clobber.cfg
new file mode 100644
index 000000000..481723782
--- /dev/null
+++ b/src/test/ref/scrollbig-clobber.cfg
@@ -0,0 +1,42 @@
+@begin: scope:[]  from
+  [0] phi()
+  to:@2
+@2: scope:[]  from @begin
+  [1] phi()
+  [2] call main 
+  to:@end
+@end: scope:[]  from @2
+  [3] phi()
+main: scope:[main]  from @2
+  [4] phi()
+  to:main::@1
+main::@1: scope:[main]  from main main::@3
+  [5] (byte) main::i#2 ← phi( main/(byte/signed byte/word/signed word/dword/signed dword) 0 main::@3/(byte) main::i#1 )
+  [5] (byte*) nxt#13 ← phi( main/(const byte*) TEXT#0 main::@3/(byte*) nxt#11 )
+  [6] call next_char 
+  [7] (byte) next_char::return#0 ← (byte) next_char::return#1
+  to:main::@3
+main::@3: scope:[main]  from main::@1
+  [8] (byte~) main::$0 ← (byte) next_char::return#0
+  [9] *((const byte*) main::SCREEN#0 + (byte) main::i#2) ← (byte~) main::$0
+  [10] (byte) main::i#1 ← ++ (byte) main::i#2
+  [11] if((byte) main::i#1!=(byte/signed byte/word/signed word/dword/signed dword) 0) goto main::@1
+  to:main::@return
+main::@return: scope:[main]  from main::@3
+  [12] return 
+  to:@return
+next_char: scope:[next_char]  from main::@1
+  [13] (byte) next_char::c#0 ← *((byte*) nxt#13)
+  [14] if((byte) next_char::c#0!=(byte) '@') goto next_char::@1
+  to:next_char::@2
+next_char::@2: scope:[next_char]  from next_char
+  [15] (byte) next_char::c#1 ← *((const byte*) TEXT#0)
+  to:next_char::@1
+next_char::@1: scope:[next_char]  from next_char next_char::@2
+  [16] (byte) next_char::return#1 ← phi( next_char/(byte) next_char::c#0 next_char::@2/(byte) next_char::c#1 )
+  [16] (byte*) nxt#10 ← phi( next_char/(byte*) nxt#13 next_char::@2/(const byte*) TEXT#0 )
+  [17] (byte*) nxt#11 ← ++ (byte*) nxt#10
+  to:next_char::@return
+next_char::@return: scope:[next_char]  from next_char::@1
+  [18] return 
+  to:@return
diff --git a/src/test/ref/scrollbig-clobber.log b/src/test/ref/scrollbig-clobber.log
new file mode 100644
index 000000000..5fcd9f9a7
--- /dev/null
+++ b/src/test/ref/scrollbig-clobber.log
@@ -0,0 +1,707 @@
+
+CONTROL FLOW GRAPH SSA
+@begin: scope:[]  from
+  (byte*) TEXT#0 ← (const string) $0
+  to:@1
+main: scope:[main]  from @2
+  (byte*) TEXT#5 ← phi( @2/(byte*) TEXT#7 )
+  (byte*) nxt#15 ← phi( @2/(byte*) nxt#14 )
+  (byte*) main::SCREEN#0 ← ((byte*)) (word/signed word/dword/signed dword) $400
+  (byte) main::i#0 ← (byte/signed byte/word/signed word/dword/signed dword) 0
+  to:main::@1
+main::@1: scope:[main]  from main main::@3
+  (byte*) TEXT#4 ← phi( main/(byte*) TEXT#5 main::@3/(byte*) TEXT#6 )
+  (byte) main::i#3 ← phi( main/(byte) main::i#0 main::@3/(byte) main::i#1 )
+  (byte*) main::SCREEN#2 ← phi( main/(byte*) main::SCREEN#0 main::@3/(byte*) main::SCREEN#1 )
+  (byte*) nxt#13 ← phi( main/(byte*) nxt#15 main::@3/(byte*) nxt#0 )
+  call next_char 
+  (byte) next_char::return#0 ← (byte) next_char::return#2
+  to:main::@3
+main::@3: scope:[main]  from main::@1
+  (byte*) TEXT#6 ← phi( main::@1/(byte*) TEXT#4 )
+  (byte) main::i#2 ← phi( main::@1/(byte) main::i#3 )
+  (byte*) main::SCREEN#1 ← phi( main::@1/(byte*) main::SCREEN#2 )
+  (byte*) nxt#7 ← phi( main::@1/(byte*) nxt#5 )
+  (byte) next_char::return#3 ← phi( main::@1/(byte) next_char::return#0 )
+  (byte~) main::$0 ← (byte) next_char::return#3
+  (byte*) nxt#0 ← (byte*) nxt#7
+  *((byte*) main::SCREEN#1 + (byte) main::i#2) ← (byte~) main::$0
+  (byte) main::i#1 ← (byte) main::i#2 + rangenext(0,$ff)
+  (bool~) main::$1 ← (byte) main::i#1 != rangelast(0,$ff)
+  if((bool~) main::$1) goto main::@1
+  to:main::@return
+main::@return: scope:[main]  from main::@3
+  (byte*) nxt#8 ← phi( main::@3/(byte*) nxt#0 )
+  (byte*) nxt#1 ← (byte*) nxt#8
+  return 
+  to:@return
+@1: scope:[]  from @begin
+  (byte*) TEXT#1 ← phi( @begin/(byte*) TEXT#0 )
+  (byte*) nxt#2 ← (byte*) TEXT#1
+  to:@2
+next_char: scope:[next_char]  from main::@1
+  (byte*) TEXT#3 ← phi( main::@1/(byte*) TEXT#4 )
+  (byte*) nxt#9 ← phi( main::@1/(byte*) nxt#13 )
+  (byte) next_char::c#0 ← *((byte*) nxt#9)
+  (bool~) next_char::$0 ← (byte) next_char::c#0 == (byte) '@'
+  (bool~) next_char::$1 ← ! (bool~) next_char::$0
+  if((bool~) next_char::$1) goto next_char::@1
+  to:next_char::@2
+next_char::@1: scope:[next_char]  from next_char next_char::@2
+  (byte) next_char::c#2 ← phi( next_char/(byte) next_char::c#0 next_char::@2/(byte) next_char::c#1 )
+  (byte*) nxt#10 ← phi( next_char/(byte*) nxt#9 next_char::@2/(byte*) nxt#4 )
+  (byte*) nxt#3 ← ++ (byte*) nxt#10
+  (byte) next_char::return#1 ← (byte) next_char::c#2
+  to:next_char::@return
+next_char::@2: scope:[next_char]  from next_char
+  (byte*) TEXT#2 ← phi( next_char/(byte*) TEXT#3 )
+  (byte*) nxt#4 ← (byte*) TEXT#2
+  (byte) next_char::c#1 ← *((byte*) nxt#4)
+  to:next_char::@1
+next_char::@return: scope:[next_char]  from next_char::@1
+  (byte*) nxt#11 ← phi( next_char::@1/(byte*) nxt#3 )
+  (byte) next_char::return#4 ← phi( next_char::@1/(byte) next_char::return#1 )
+  (byte) next_char::return#2 ← (byte) next_char::return#4
+  (byte*) nxt#5 ← (byte*) nxt#11
+  return 
+  to:@return
+@2: scope:[]  from @1
+  (byte*) TEXT#7 ← phi( @1/(byte*) TEXT#1 )
+  (byte*) nxt#14 ← phi( @1/(byte*) nxt#2 )
+  call main 
+  to:@3
+@3: scope:[]  from @2
+  (byte*) nxt#12 ← phi( @2/(byte*) nxt#1 )
+  (byte*) nxt#6 ← (byte*) nxt#12
+  to:@end
+@end: scope:[]  from @3
+
+SYMBOL TABLE SSA
+(const string) $0 = (string) "cml @"
+(label) @1
+(label) @2
+(label) @3
+(label) @begin
+(label) @end
+(byte*) TEXT
+(byte*) TEXT#0
+(byte*) TEXT#1
+(byte*) TEXT#2
+(byte*) TEXT#3
+(byte*) TEXT#4
+(byte*) TEXT#5
+(byte*) TEXT#6
+(byte*) TEXT#7
+(void()) main()
+(byte~) main::$0
+(bool~) main::$1
+(label) main::@1
+(label) main::@3
+(label) main::@return
+(byte*) main::SCREEN
+(byte*) main::SCREEN#0
+(byte*) main::SCREEN#1
+(byte*) main::SCREEN#2
+(byte) main::i
+(byte) main::i#0
+(byte) main::i#1
+(byte) main::i#2
+(byte) main::i#3
+(byte()) next_char()
+(bool~) next_char::$0
+(bool~) next_char::$1
+(label) next_char::@1
+(label) next_char::@2
+(label) next_char::@return
+(byte) next_char::c
+(byte) next_char::c#0
+(byte) next_char::c#1
+(byte) next_char::c#2
+(byte) next_char::return
+(byte) next_char::return#0
+(byte) next_char::return#1
+(byte) next_char::return#2
+(byte) next_char::return#3
+(byte) next_char::return#4
+(byte*) nxt
+(byte*) nxt#0
+(byte*) nxt#1
+(byte*) nxt#10
+(byte*) nxt#11
+(byte*) nxt#12
+(byte*) nxt#13
+(byte*) nxt#14
+(byte*) nxt#15
+(byte*) nxt#2
+(byte*) nxt#3
+(byte*) nxt#4
+(byte*) nxt#5
+(byte*) nxt#6
+(byte*) nxt#7
+(byte*) nxt#8
+(byte*) nxt#9
+
+Inversing boolean not [22] (bool~) next_char::$1 ← (byte) next_char::c#0 != (byte) '@' from [21] (bool~) next_char::$0 ← (byte) next_char::c#0 == (byte) '@'
+Successful SSA optimization Pass2UnaryNotSimplification
+Alias (byte) next_char::return#0 = (byte) next_char::return#3 
+Alias (byte*) main::SCREEN#1 = (byte*) main::SCREEN#2 
+Alias (byte) main::i#2 = (byte) main::i#3 
+Alias (byte*) TEXT#4 = (byte*) TEXT#6 
+Alias (byte*) nxt#0 = (byte*) nxt#7 (byte*) nxt#8 (byte*) nxt#1 
+Alias (byte*) TEXT#0 = (byte*) TEXT#1 (byte*) nxt#2 (byte*) nxt#14 (byte*) TEXT#7 
+Alias (byte) next_char::return#1 = (byte) next_char::c#2 (byte) next_char::return#4 (byte) next_char::return#2 
+Alias (byte*) TEXT#2 = (byte*) TEXT#3 (byte*) nxt#4 
+Alias (byte*) nxt#11 = (byte*) nxt#3 (byte*) nxt#5 
+Alias (byte*) nxt#12 = (byte*) nxt#6 
+Successful SSA optimization Pass2AliasElimination
+Self Phi Eliminated (byte*) main::SCREEN#1
+Self Phi Eliminated (byte*) TEXT#4
+Successful SSA optimization Pass2SelfPhiElimination
+Redundant Phi (byte*) nxt#15 (byte*) TEXT#0
+Redundant Phi (byte*) TEXT#5 (byte*) TEXT#0
+Redundant Phi (byte*) main::SCREEN#1 (byte*) main::SCREEN#0
+Redundant Phi (byte*) TEXT#4 (byte*) TEXT#5
+Redundant Phi (byte*) nxt#0 (byte*) nxt#11
+Redundant Phi (byte*) nxt#9 (byte*) nxt#13
+Redundant Phi (byte*) TEXT#2 (byte*) TEXT#4
+Redundant Phi (byte*) nxt#12 (byte*) nxt#0
+Successful SSA optimization Pass2RedundantPhiElimination
+Simple Condition (bool~) main::$1 [13] if((byte) main::i#1!=rangelast(0,$ff)) goto main::@1
+Simple Condition (bool~) next_char::$1 [23] if((byte) next_char::c#0!=(byte) '@') goto next_char::@1
+Successful SSA optimization Pass2ConditionalJumpSimplification
+Constant (const byte*) TEXT#0 = $0
+Constant (const byte*) main::SCREEN#0 = ((byte*))$400
+Constant (const byte) main::i#0 = 0
+Successful SSA optimization Pass2ConstantIdentification
+Resolved ranged next value main::i#1 ← ++ main::i#2 to ++
+Resolved ranged comparison value if(main::i#1!=rangelast(0,$ff)) goto main::@1 to (byte/signed byte/word/signed word/dword/signed dword) 0
+Culled Empty Block (label) @1
+Culled Empty Block (label) @3
+Successful SSA optimization Pass2CullEmptyBlocks
+Inlining constant with var siblings (const byte) main::i#0
+Constant inlined $0 = (const byte*) TEXT#0
+Constant inlined main::i#0 = (byte/signed byte/word/signed word/dword/signed dword) 0
+Successful SSA optimization Pass2ConstantInlining
+Added new block during phi lifting main::@4(between main::@3 and main::@1)
+Added new block during phi lifting next_char::@4(between next_char and next_char::@1)
+Adding NOP phi() at start of @begin
+Adding NOP phi() at start of @2
+Adding NOP phi() at start of @end
+Adding NOP phi() at start of main
+CALL GRAPH
+Calls in [] to main:2 
+Calls in [main] to next_char:6 
+
+Created 4 initial phi equivalence classes
+Coalesced [13] nxt#16 ← nxt#11
+Coalesced [14] main::i#4 ← main::i#1
+Coalesced [18] next_char::return#6 ← next_char::c#1
+Coalesced [22] nxt#17 ← nxt#13
+Coalesced [23] next_char::return#5 ← next_char::c#0
+Coalesced down to 3 phi equivalence classes
+Culled Empty Block (label) main::@4
+Culled Empty Block (label) next_char::@4
+Adding NOP phi() at start of @begin
+Adding NOP phi() at start of @2
+Adding NOP phi() at start of @end
+Adding NOP phi() at start of main
+
+FINAL CONTROL FLOW GRAPH
+@begin: scope:[]  from
+  [0] phi()
+  to:@2
+@2: scope:[]  from @begin
+  [1] phi()
+  [2] call main 
+  to:@end
+@end: scope:[]  from @2
+  [3] phi()
+main: scope:[main]  from @2
+  [4] phi()
+  to:main::@1
+main::@1: scope:[main]  from main main::@3
+  [5] (byte) main::i#2 ← phi( main/(byte/signed byte/word/signed word/dword/signed dword) 0 main::@3/(byte) main::i#1 )
+  [5] (byte*) nxt#13 ← phi( main/(const byte*) TEXT#0 main::@3/(byte*) nxt#11 )
+  [6] call next_char 
+  [7] (byte) next_char::return#0 ← (byte) next_char::return#1
+  to:main::@3
+main::@3: scope:[main]  from main::@1
+  [8] (byte~) main::$0 ← (byte) next_char::return#0
+  [9] *((const byte*) main::SCREEN#0 + (byte) main::i#2) ← (byte~) main::$0
+  [10] (byte) main::i#1 ← ++ (byte) main::i#2
+  [11] if((byte) main::i#1!=(byte/signed byte/word/signed word/dword/signed dword) 0) goto main::@1
+  to:main::@return
+main::@return: scope:[main]  from main::@3
+  [12] return 
+  to:@return
+next_char: scope:[next_char]  from main::@1
+  [13] (byte) next_char::c#0 ← *((byte*) nxt#13)
+  [14] if((byte) next_char::c#0!=(byte) '@') goto next_char::@1
+  to:next_char::@2
+next_char::@2: scope:[next_char]  from next_char
+  [15] (byte) next_char::c#1 ← *((const byte*) TEXT#0)
+  to:next_char::@1
+next_char::@1: scope:[next_char]  from next_char next_char::@2
+  [16] (byte) next_char::return#1 ← phi( next_char/(byte) next_char::c#0 next_char::@2/(byte) next_char::c#1 )
+  [16] (byte*) nxt#10 ← phi( next_char/(byte*) nxt#13 next_char::@2/(const byte*) TEXT#0 )
+  [17] (byte*) nxt#11 ← ++ (byte*) nxt#10
+  to:next_char::@return
+next_char::@return: scope:[next_char]  from next_char::@1
+  [18] return 
+  to:@return
+
+
+VARIABLE REGISTER WEIGHTS
+(byte*) TEXT
+(void()) main()
+(byte~) main::$0 22.0
+(byte*) main::SCREEN
+(byte) main::i
+(byte) main::i#1 16.5
+(byte) main::i#2 6.6000000000000005
+(byte()) next_char()
+(byte) next_char::c
+(byte) next_char::c#0 3.0
+(byte) next_char::c#1 4.0
+(byte) next_char::return
+(byte) next_char::return#0 22.0
+(byte) next_char::return#1 3.75
+(byte*) nxt
+(byte*) nxt#10 4.0
+(byte*) nxt#11 1.625
+(byte*) nxt#13 5.0
+
+Initial phi equivalence classes
+[ main::i#2 main::i#1 ]
+[ nxt#10 nxt#13 nxt#11 ]
+[ next_char::return#1 next_char::c#0 next_char::c#1 ]
+Added variable next_char::return#0 to zero page equivalence class [ next_char::return#0 ]
+Added variable main::$0 to zero page equivalence class [ main::$0 ]
+Complete equivalence classes
+[ main::i#2 main::i#1 ]
+[ nxt#10 nxt#13 nxt#11 ]
+[ next_char::return#1 next_char::c#0 next_char::c#1 ]
+[ next_char::return#0 ]
+[ main::$0 ]
+Allocated zp ZP_BYTE:2 [ main::i#2 main::i#1 ]
+Allocated zp ZP_WORD:3 [ nxt#10 nxt#13 nxt#11 ]
+Allocated zp ZP_BYTE:5 [ next_char::return#1 next_char::c#0 next_char::c#1 ]
+Allocated zp ZP_BYTE:6 [ next_char::return#0 ]
+Allocated zp ZP_BYTE:7 [ main::$0 ]
+
+INITIAL ASM
+//SEG0 File Comments
+// Clobber problem in next_char return value
+//SEG1 Basic Upstart
+.pc = $801 "Basic"
+:BasicUpstart(bbegin)
+.pc = $80d "Program"
+//SEG2 Global Constants & labels
+  .label nxt = 3
+//SEG3 @begin
+bbegin:
+//SEG4 [1] phi from @begin to @2 [phi:@begin->@2]
+b2_from_bbegin:
+  jmp b2
+//SEG5 @2
+b2:
+//SEG6 [2] call main 
+//SEG7 [4] phi from @2 to main [phi:@2->main]
+main_from_b2:
+  jsr main
+//SEG8 [3] phi from @2 to @end [phi:@2->@end]
+bend_from_b2:
+  jmp bend
+//SEG9 @end
+bend:
+//SEG10 main
+main: {
+    .label SCREEN = $400
+    .label _0 = 7
+    .label i = 2
+  //SEG11 [5] phi from main to main::@1 [phi:main->main::@1]
+  b1_from_main:
+  //SEG12 [5] phi (byte) main::i#2 = (byte/signed byte/word/signed word/dword/signed dword) 0 [phi:main->main::@1#0] -- vbuz1=vbuc1 
+    lda #0
+    sta i
+  //SEG13 [5] phi (byte*) nxt#13 = (const byte*) TEXT#0 [phi:main->main::@1#1] -- pbuz1=pbuc1 
+    lda #<TEXT
+    sta nxt
+    lda #>TEXT
+    sta nxt+1
+    jmp b1
+  //SEG14 [5] phi from main::@3 to main::@1 [phi:main::@3->main::@1]
+  b1_from_b3:
+  //SEG15 [5] phi (byte) main::i#2 = (byte) main::i#1 [phi:main::@3->main::@1#0] -- register_copy 
+  //SEG16 [5] phi (byte*) nxt#13 = (byte*) nxt#11 [phi:main::@3->main::@1#1] -- register_copy 
+    jmp b1
+  //SEG17 main::@1
+  b1:
+  //SEG18 [6] call next_char 
+    jsr next_char
+  //SEG19 [7] (byte) next_char::return#0 ← (byte) next_char::return#1 -- vbuz1=vbuz2 
+    lda next_char.return_1
+    sta next_char.return
+    jmp b3
+  //SEG20 main::@3
+  b3:
+  //SEG21 [8] (byte~) main::$0 ← (byte) next_char::return#0 -- vbuz1=vbuz2 
+    lda next_char.return
+    sta _0
+  //SEG22 [9] *((const byte*) main::SCREEN#0 + (byte) main::i#2) ← (byte~) main::$0 -- pbuc1_derefidx_vbuz1=vbuz2 
+    lda _0
+    ldy i
+    sta SCREEN,y
+  //SEG23 [10] (byte) main::i#1 ← ++ (byte) main::i#2 -- vbuz1=_inc_vbuz1 
+    inc i
+  //SEG24 [11] if((byte) main::i#1!=(byte/signed byte/word/signed word/dword/signed dword) 0) goto main::@1 -- vbuz1_neq_0_then_la1 
+    lda i
+    cmp #0
+    bne b1_from_b3
+    jmp breturn
+  //SEG25 main::@return
+  breturn:
+  //SEG26 [12] return 
+    rts
+}
+//SEG27 next_char
+// Find the next char of the text
+next_char: {
+    .label return = 6
+    .label c = 5
+    .label return_1 = 5
+  //SEG28 [13] (byte) next_char::c#0 ← *((byte*) nxt#13) -- vbuz1=_deref_pbuz2 
+    ldy #0
+    lda (nxt),y
+    sta c
+  //SEG29 [14] if((byte) next_char::c#0!=(byte) '@') goto next_char::@1 -- vbuz1_neq_vbuc1_then_la1 
+    lda c
+    cmp #'@'
+    bne b1_from_next_char
+    jmp b2
+  //SEG30 next_char::@2
+  b2:
+  //SEG31 [15] (byte) next_char::c#1 ← *((const byte*) TEXT#0) -- vbuz1=_deref_pbuc1 
+    lda TEXT
+    sta c
+  //SEG32 [16] phi from next_char::@2 to next_char::@1 [phi:next_char::@2->next_char::@1]
+  b1_from_b2:
+  //SEG33 [16] phi (byte) next_char::return#1 = (byte) next_char::c#1 [phi:next_char::@2->next_char::@1#0] -- register_copy 
+  //SEG34 [16] phi (byte*) nxt#10 = (const byte*) TEXT#0 [phi:next_char::@2->next_char::@1#1] -- pbuz1=pbuc1 
+    lda #<TEXT
+    sta nxt
+    lda #>TEXT
+    sta nxt+1
+    jmp b1
+  //SEG35 [16] phi from next_char to next_char::@1 [phi:next_char->next_char::@1]
+  b1_from_next_char:
+  //SEG36 [16] phi (byte) next_char::return#1 = (byte) next_char::c#0 [phi:next_char->next_char::@1#0] -- register_copy 
+  //SEG37 [16] phi (byte*) nxt#10 = (byte*) nxt#13 [phi:next_char->next_char::@1#1] -- register_copy 
+    jmp b1
+  //SEG38 next_char::@1
+  b1:
+  //SEG39 [17] (byte*) nxt#11 ← ++ (byte*) nxt#10 -- pbuz1=_inc_pbuz1 
+    inc nxt
+    bne !+
+    inc nxt+1
+  !:
+    jmp breturn
+  //SEG40 next_char::@return
+  breturn:
+  //SEG41 [18] return 
+    rts
+}
+  TEXT: .text "cml @"
+
+REGISTER UPLIFT POTENTIAL REGISTERS
+Statement [13] (byte) next_char::c#0 ← *((byte*) nxt#13) [ nxt#13 next_char::c#0 ] ( main:2::next_char:6 [ main::i#2 nxt#13 next_char::c#0 ] ) always clobbers reg byte a reg byte y 
+Removing always clobbered register reg byte a as potential for zp ZP_BYTE:2 [ main::i#2 main::i#1 ]
+Removing always clobbered register reg byte y as potential for zp ZP_BYTE:2 [ main::i#2 main::i#1 ]
+Statement [13] (byte) next_char::c#0 ← *((byte*) nxt#13) [ nxt#13 next_char::c#0 ] ( main:2::next_char:6 [ main::i#2 nxt#13 next_char::c#0 ] ) always clobbers reg byte a reg byte y 
+Potential registers zp ZP_BYTE:2 [ main::i#2 main::i#1 ] : zp ZP_BYTE:2 , reg byte x , 
+Potential registers zp ZP_WORD:3 [ nxt#10 nxt#13 nxt#11 ] : zp ZP_WORD:3 , 
+Potential registers zp ZP_BYTE:5 [ next_char::return#1 next_char::c#0 next_char::c#1 ] : zp ZP_BYTE:5 , reg byte a , reg byte x , reg byte y , 
+Potential registers zp ZP_BYTE:6 [ next_char::return#0 ] : zp ZP_BYTE:6 , reg byte a , reg byte x , reg byte y , 
+Potential registers zp ZP_BYTE:7 [ main::$0 ] : zp ZP_BYTE:7 , reg byte a , reg byte x , reg byte y , 
+
+REGISTER UPLIFT SCOPES
+Uplift Scope [main] 23.1: zp ZP_BYTE:2 [ main::i#2 main::i#1 ] 22: zp ZP_BYTE:7 [ main::$0 ] 
+Uplift Scope [next_char] 22: zp ZP_BYTE:6 [ next_char::return#0 ] 10.75: zp ZP_BYTE:5 [ next_char::return#1 next_char::c#0 next_char::c#1 ] 
+Uplift Scope [] 10.62: zp ZP_WORD:3 [ nxt#10 nxt#13 nxt#11 ] 
+
+Uplifting [main] best 587 combination reg byte x [ main::i#2 main::i#1 ] reg byte a [ main::$0 ] 
+Uplifting [next_char] best 510 combination reg byte a [ next_char::return#0 ] reg byte y [ next_char::return#1 next_char::c#0 next_char::c#1 ] 
+Uplifting [] best 510 combination zp ZP_WORD:3 [ nxt#10 nxt#13 nxt#11 ] 
+Allocated (was zp ZP_WORD:3) zp ZP_WORD:2 [ nxt#10 nxt#13 nxt#11 ]
+
+ASSEMBLER BEFORE OPTIMIZATION
+//SEG0 File Comments
+// Clobber problem in next_char return value
+//SEG1 Basic Upstart
+.pc = $801 "Basic"
+:BasicUpstart(bbegin)
+.pc = $80d "Program"
+//SEG2 Global Constants & labels
+  .label nxt = 2
+//SEG3 @begin
+bbegin:
+//SEG4 [1] phi from @begin to @2 [phi:@begin->@2]
+b2_from_bbegin:
+  jmp b2
+//SEG5 @2
+b2:
+//SEG6 [2] call main 
+//SEG7 [4] phi from @2 to main [phi:@2->main]
+main_from_b2:
+  jsr main
+//SEG8 [3] phi from @2 to @end [phi:@2->@end]
+bend_from_b2:
+  jmp bend
+//SEG9 @end
+bend:
+//SEG10 main
+main: {
+    .label SCREEN = $400
+  //SEG11 [5] phi from main to main::@1 [phi:main->main::@1]
+  b1_from_main:
+  //SEG12 [5] phi (byte) main::i#2 = (byte/signed byte/word/signed word/dword/signed dword) 0 [phi:main->main::@1#0] -- vbuxx=vbuc1 
+    ldx #0
+  //SEG13 [5] phi (byte*) nxt#13 = (const byte*) TEXT#0 [phi:main->main::@1#1] -- pbuz1=pbuc1 
+    lda #<TEXT
+    sta nxt
+    lda #>TEXT
+    sta nxt+1
+    jmp b1
+  //SEG14 [5] phi from main::@3 to main::@1 [phi:main::@3->main::@1]
+  b1_from_b3:
+  //SEG15 [5] phi (byte) main::i#2 = (byte) main::i#1 [phi:main::@3->main::@1#0] -- register_copy 
+  //SEG16 [5] phi (byte*) nxt#13 = (byte*) nxt#11 [phi:main::@3->main::@1#1] -- register_copy 
+    jmp b1
+  //SEG17 main::@1
+  b1:
+  //SEG18 [6] call next_char 
+    jsr next_char
+  //SEG19 [7] (byte) next_char::return#0 ← (byte) next_char::return#1 -- vbuaa=vbuyy 
+    tya
+    jmp b3
+  //SEG20 main::@3
+  b3:
+  //SEG21 [8] (byte~) main::$0 ← (byte) next_char::return#0
+  //SEG22 [9] *((const byte*) main::SCREEN#0 + (byte) main::i#2) ← (byte~) main::$0 -- pbuc1_derefidx_vbuxx=vbuaa 
+    sta SCREEN,x
+  //SEG23 [10] (byte) main::i#1 ← ++ (byte) main::i#2 -- vbuxx=_inc_vbuxx 
+    inx
+  //SEG24 [11] if((byte) main::i#1!=(byte/signed byte/word/signed word/dword/signed dword) 0) goto main::@1 -- vbuxx_neq_0_then_la1 
+    cpx #0
+    bne b1_from_b3
+    jmp breturn
+  //SEG25 main::@return
+  breturn:
+  //SEG26 [12] return 
+    rts
+}
+//SEG27 next_char
+// Find the next char of the text
+next_char: {
+  //SEG28 [13] (byte) next_char::c#0 ← *((byte*) nxt#13) -- vbuyy=_deref_pbuz1 
+    ldy #0
+    lda (nxt),y
+    tay
+  //SEG29 [14] if((byte) next_char::c#0!=(byte) '@') goto next_char::@1 -- vbuyy_neq_vbuc1_then_la1 
+    cpy #'@'
+    bne b1_from_next_char
+    jmp b2
+  //SEG30 next_char::@2
+  b2:
+  //SEG31 [15] (byte) next_char::c#1 ← *((const byte*) TEXT#0) -- vbuyy=_deref_pbuc1 
+    ldy TEXT
+  //SEG32 [16] phi from next_char::@2 to next_char::@1 [phi:next_char::@2->next_char::@1]
+  b1_from_b2:
+  //SEG33 [16] phi (byte) next_char::return#1 = (byte) next_char::c#1 [phi:next_char::@2->next_char::@1#0] -- register_copy 
+  //SEG34 [16] phi (byte*) nxt#10 = (const byte*) TEXT#0 [phi:next_char::@2->next_char::@1#1] -- pbuz1=pbuc1 
+    lda #<TEXT
+    sta nxt
+    lda #>TEXT
+    sta nxt+1
+    jmp b1
+  //SEG35 [16] phi from next_char to next_char::@1 [phi:next_char->next_char::@1]
+  b1_from_next_char:
+  //SEG36 [16] phi (byte) next_char::return#1 = (byte) next_char::c#0 [phi:next_char->next_char::@1#0] -- register_copy 
+  //SEG37 [16] phi (byte*) nxt#10 = (byte*) nxt#13 [phi:next_char->next_char::@1#1] -- register_copy 
+    jmp b1
+  //SEG38 next_char::@1
+  b1:
+  //SEG39 [17] (byte*) nxt#11 ← ++ (byte*) nxt#10 -- pbuz1=_inc_pbuz1 
+    inc nxt
+    bne !+
+    inc nxt+1
+  !:
+    jmp breturn
+  //SEG40 next_char::@return
+  breturn:
+  //SEG41 [18] return 
+    rts
+}
+  TEXT: .text "cml @"
+
+ASSEMBLER OPTIMIZATIONS
+Removing instruction jmp b2
+Removing instruction jmp bend
+Removing instruction jmp b1
+Removing instruction jmp b3
+Removing instruction jmp breturn
+Removing instruction jmp b2
+Removing instruction jmp b1
+Removing instruction jmp breturn
+Succesful ASM optimization Pass5NextJumpElimination
+Replacing label b1_from_b3 with b1
+Replacing label b1_from_next_char with b1
+Removing instruction b2_from_bbegin:
+Removing instruction b2:
+Removing instruction main_from_b2:
+Removing instruction bend_from_b2:
+Removing instruction b1_from_b3:
+Removing instruction b1_from_next_char:
+Succesful ASM optimization Pass5RedundantLabelElimination
+Removing instruction bend:
+Removing instruction b1_from_main:
+Removing instruction b3:
+Removing instruction breturn:
+Removing instruction b2:
+Removing instruction b1_from_b2:
+Removing instruction breturn:
+Succesful ASM optimization Pass5UnusedLabelElimination
+Updating BasicUpstart to call main directly
+Removing instruction jsr main
+Succesful ASM optimization Pass5SkipBegin
+Removing instruction jmp b1
+Removing instruction jmp b1
+Succesful ASM optimization Pass5NextJumpElimination
+Removing instruction bbegin:
+Succesful ASM optimization Pass5UnusedLabelElimination
+
+FINAL SYMBOL TABLE
+(label) @2
+(label) @begin
+(label) @end
+(byte*) TEXT
+(const byte*) TEXT#0 TEXT = (string) "cml @"
+(void()) main()
+(byte~) main::$0 reg byte a 22.0
+(label) main::@1
+(label) main::@3
+(label) main::@return
+(byte*) main::SCREEN
+(const byte*) main::SCREEN#0 SCREEN = ((byte*))(word/signed word/dword/signed dword) $400
+(byte) main::i
+(byte) main::i#1 reg byte x 16.5
+(byte) main::i#2 reg byte x 6.6000000000000005
+(byte()) next_char()
+(label) next_char::@1
+(label) next_char::@2
+(label) next_char::@return
+(byte) next_char::c
+(byte) next_char::c#0 reg byte y 3.0
+(byte) next_char::c#1 reg byte y 4.0
+(byte) next_char::return
+(byte) next_char::return#0 reg byte a 22.0
+(byte) next_char::return#1 reg byte y 3.75
+(byte*) nxt
+(byte*) nxt#10 nxt zp ZP_WORD:2 4.0
+(byte*) nxt#11 nxt zp ZP_WORD:2 1.625
+(byte*) nxt#13 nxt zp ZP_WORD:2 5.0
+
+reg byte x [ main::i#2 main::i#1 ]
+zp ZP_WORD:2 [ nxt#10 nxt#13 nxt#11 ]
+reg byte y [ next_char::return#1 next_char::c#0 next_char::c#1 ]
+reg byte a [ next_char::return#0 ]
+reg byte a [ main::$0 ]
+
+
+FINAL ASSEMBLER
+Score: 366
+
+//SEG0 File Comments
+// Clobber problem in next_char return value
+//SEG1 Basic Upstart
+.pc = $801 "Basic"
+:BasicUpstart(main)
+.pc = $80d "Program"
+//SEG2 Global Constants & labels
+  .label nxt = 2
+//SEG3 @begin
+//SEG4 [1] phi from @begin to @2 [phi:@begin->@2]
+//SEG5 @2
+//SEG6 [2] call main 
+//SEG7 [4] phi from @2 to main [phi:@2->main]
+//SEG8 [3] phi from @2 to @end [phi:@2->@end]
+//SEG9 @end
+//SEG10 main
+main: {
+    .label SCREEN = $400
+  //SEG11 [5] phi from main to main::@1 [phi:main->main::@1]
+  //SEG12 [5] phi (byte) main::i#2 = (byte/signed byte/word/signed word/dword/signed dword) 0 [phi:main->main::@1#0] -- vbuxx=vbuc1 
+    ldx #0
+  //SEG13 [5] phi (byte*) nxt#13 = (const byte*) TEXT#0 [phi:main->main::@1#1] -- pbuz1=pbuc1 
+    lda #<TEXT
+    sta nxt
+    lda #>TEXT
+    sta nxt+1
+  //SEG14 [5] phi from main::@3 to main::@1 [phi:main::@3->main::@1]
+  //SEG15 [5] phi (byte) main::i#2 = (byte) main::i#1 [phi:main::@3->main::@1#0] -- register_copy 
+  //SEG16 [5] phi (byte*) nxt#13 = (byte*) nxt#11 [phi:main::@3->main::@1#1] -- register_copy 
+  //SEG17 main::@1
+  b1:
+  //SEG18 [6] call next_char 
+    jsr next_char
+  //SEG19 [7] (byte) next_char::return#0 ← (byte) next_char::return#1 -- vbuaa=vbuyy 
+    tya
+  //SEG20 main::@3
+  //SEG21 [8] (byte~) main::$0 ← (byte) next_char::return#0
+  //SEG22 [9] *((const byte*) main::SCREEN#0 + (byte) main::i#2) ← (byte~) main::$0 -- pbuc1_derefidx_vbuxx=vbuaa 
+    sta SCREEN,x
+  //SEG23 [10] (byte) main::i#1 ← ++ (byte) main::i#2 -- vbuxx=_inc_vbuxx 
+    inx
+  //SEG24 [11] if((byte) main::i#1!=(byte/signed byte/word/signed word/dword/signed dword) 0) goto main::@1 -- vbuxx_neq_0_then_la1 
+    cpx #0
+    bne b1
+  //SEG25 main::@return
+  //SEG26 [12] return 
+    rts
+}
+//SEG27 next_char
+// Find the next char of the text
+next_char: {
+  //SEG28 [13] (byte) next_char::c#0 ← *((byte*) nxt#13) -- vbuyy=_deref_pbuz1 
+    ldy #0
+    lda (nxt),y
+    tay
+  //SEG29 [14] if((byte) next_char::c#0!=(byte) '@') goto next_char::@1 -- vbuyy_neq_vbuc1_then_la1 
+    cpy #'@'
+    bne b1
+  //SEG30 next_char::@2
+  //SEG31 [15] (byte) next_char::c#1 ← *((const byte*) TEXT#0) -- vbuyy=_deref_pbuc1 
+    ldy TEXT
+  //SEG32 [16] phi from next_char::@2 to next_char::@1 [phi:next_char::@2->next_char::@1]
+  //SEG33 [16] phi (byte) next_char::return#1 = (byte) next_char::c#1 [phi:next_char::@2->next_char::@1#0] -- register_copy 
+  //SEG34 [16] phi (byte*) nxt#10 = (const byte*) TEXT#0 [phi:next_char::@2->next_char::@1#1] -- pbuz1=pbuc1 
+    lda #<TEXT
+    sta nxt
+    lda #>TEXT
+    sta nxt+1
+  //SEG35 [16] phi from next_char to next_char::@1 [phi:next_char->next_char::@1]
+  //SEG36 [16] phi (byte) next_char::return#1 = (byte) next_char::c#0 [phi:next_char->next_char::@1#0] -- register_copy 
+  //SEG37 [16] phi (byte*) nxt#10 = (byte*) nxt#13 [phi:next_char->next_char::@1#1] -- register_copy 
+  //SEG38 next_char::@1
+  b1:
+  //SEG39 [17] (byte*) nxt#11 ← ++ (byte*) nxt#10 -- pbuz1=_inc_pbuz1 
+    inc nxt
+    bne !+
+    inc nxt+1
+  !:
+  //SEG40 next_char::@return
+  //SEG41 [18] return 
+    rts
+}
+  TEXT: .text "cml @"
+
diff --git a/src/test/ref/scrollbig-clobber.sym b/src/test/ref/scrollbig-clobber.sym
new file mode 100644
index 000000000..23569856c
--- /dev/null
+++ b/src/test/ref/scrollbig-clobber.sym
@@ -0,0 +1,35 @@
+(label) @2
+(label) @begin
+(label) @end
+(byte*) TEXT
+(const byte*) TEXT#0 TEXT = (string) "cml @"
+(void()) main()
+(byte~) main::$0 reg byte a 22.0
+(label) main::@1
+(label) main::@3
+(label) main::@return
+(byte*) main::SCREEN
+(const byte*) main::SCREEN#0 SCREEN = ((byte*))(word/signed word/dword/signed dword) $400
+(byte) main::i
+(byte) main::i#1 reg byte x 16.5
+(byte) main::i#2 reg byte x 6.6000000000000005
+(byte()) next_char()
+(label) next_char::@1
+(label) next_char::@2
+(label) next_char::@return
+(byte) next_char::c
+(byte) next_char::c#0 reg byte y 3.0
+(byte) next_char::c#1 reg byte y 4.0
+(byte) next_char::return
+(byte) next_char::return#0 reg byte a 22.0
+(byte) next_char::return#1 reg byte y 3.75
+(byte*) nxt
+(byte*) nxt#10 nxt zp ZP_WORD:2 4.0
+(byte*) nxt#11 nxt zp ZP_WORD:2 1.625
+(byte*) nxt#13 nxt zp ZP_WORD:2 5.0
+
+reg byte x [ main::i#2 main::i#1 ]
+zp ZP_WORD:2 [ nxt#10 nxt#13 nxt#11 ]
+reg byte y [ next_char::return#1 next_char::c#0 next_char::c#1 ]
+reg byte a [ next_char::return#0 ]
+reg byte a [ main::$0 ]