From 6f4a1f055595f39a27f4de387b549397290dbe9c Mon Sep 17 00:00:00 2001
From: jespergravgaard <jesper@balmangravgaard.dk>
Date: Sat, 6 Jul 2019 11:00:15 +0200
Subject: [PATCH] Tetris NPE has been fixed.

---
 .../dk/camelot64/kickc/test/TestPrograms.java |   2 +-
 src/test/ref/tetris-npe.asm                   |  22 +
 src/test/ref/tetris-npe.cfg                   |  27 +
 src/test/ref/tetris-npe.log                   | 537 ++++++++++++++++++
 src/test/ref/tetris-npe.sym                   |  23 +
 5 files changed, 610 insertions(+), 1 deletion(-)
 create mode 100644 src/test/ref/tetris-npe.asm
 create mode 100644 src/test/ref/tetris-npe.cfg
 create mode 100644 src/test/ref/tetris-npe.log
 create mode 100644 src/test/ref/tetris-npe.sym

diff --git a/src/test/java/dk/camelot64/kickc/test/TestPrograms.java b/src/test/java/dk/camelot64/kickc/test/TestPrograms.java
index ec5ea2b15..c4c7872e9 100644
--- a/src/test/java/dk/camelot64/kickc/test/TestPrograms.java
+++ b/src/test/java/dk/camelot64/kickc/test/TestPrograms.java
@@ -1218,12 +1218,12 @@ public class TestPrograms {
       compileAndCompare("const-if-problem");
    }
 
-   /*
    @Test
    public void testTetrisNullPointer() throws IOException, URISyntaxException {
       compileAndCompare("tetris-npe");
    }
 
+   /*
    @Test
    public void testUnrollCall() throws IOException, URISyntaxException {
       compileAndCompare("unroll-call");
diff --git a/src/test/ref/tetris-npe.asm b/src/test/ref/tetris-npe.asm
new file mode 100644
index 000000000..fcfb511ed
--- /dev/null
+++ b/src/test/ref/tetris-npe.asm
@@ -0,0 +1,22 @@
+// NullPointerException using current_movedown_rate in the main loop
+.pc = $801 "Basic"
+:BasicUpstart(main)
+.pc = $80d "Program"
+  .label RASTER = $d012
+  .label SCREEN = $400
+  .const RATE = $32
+main: {
+    ldx #0
+    ldy #RATE
+  b2:
+    lda #$ff
+    cmp RASTER
+    bne b2
+    dey
+    cpy #0
+    bne b2
+    inx
+    stx SCREEN
+    ldy #RATE
+    jmp b2
+}
diff --git a/src/test/ref/tetris-npe.cfg b/src/test/ref/tetris-npe.cfg
new file mode 100644
index 000000000..571777991
--- /dev/null
+++ b/src/test/ref/tetris-npe.cfg
@@ -0,0 +1,27 @@
+@begin: scope:[]  from
+  [0] phi()
+  to:@1
+@1: scope:[]  from @begin
+  [1] phi()
+  [2] call main 
+  to:@end
+@end: scope:[]  from @1
+  [3] phi()
+main: scope:[main]  from @1
+  [4] phi()
+  to:main::@1
+main::@1: scope:[main]  from main main::@3 main::@4
+  [5] (byte) ypos#2 ← phi( main/(byte) 0 main::@4/(byte) ypos#1 )
+  [5] (byte) counter#3 ← phi( main/(const byte) RATE#0 main::@4/(const byte) RATE#0 main::@3/(byte) counter#1 )
+  to:main::@2
+main::@2: scope:[main]  from main::@1 main::@2
+  [6] if(*((const byte*) RASTER#0)!=(byte) $ff) goto main::@2
+  to:main::@3
+main::@3: scope:[main]  from main::@2
+  [7] (byte) counter#1 ← -- (byte) counter#3
+  [8] if((byte) counter#1!=(byte) 0) goto main::@1
+  to:main::@4
+main::@4: scope:[main]  from main::@3
+  [9] (byte) ypos#1 ← ++ (byte) ypos#2
+  [10] *((const byte*) SCREEN#0) ← (byte) ypos#1
+  to:main::@1
diff --git a/src/test/ref/tetris-npe.log b/src/test/ref/tetris-npe.log
new file mode 100644
index 000000000..ad82604f2
--- /dev/null
+++ b/src/test/ref/tetris-npe.log
@@ -0,0 +1,537 @@
+Identified constant variable (byte*) RASTER
+Identified constant variable (byte*) SCREEN
+Identified constant variable (byte) RATE
+Culled Empty Block (label) main::@2
+Culled Empty Block (label) main::@12
+Culled Empty Block (label) main::@3
+Culled Empty Block (label) main::@13
+Culled Empty Block (label) main::@5
+Culled Empty Block (label) main::@7
+Culled Empty Block (label) main::@8
+Culled Empty Block (label) main::@9
+Culled Empty Block (label) main::@11
+Culled Empty Block (label) main::@14
+
+CONTROL FLOW GRAPH SSA
+@begin: scope:[]  from
+  (byte*) RASTER#0 ← ((byte*)) (number) $d012
+  (byte*) SCREEN#0 ← ((byte*)) (number) $400
+  (byte) ypos#0 ← (number) 0
+  (byte) RATE#0 ← (number) $32
+  (byte) counter#0 ← (byte) RATE#0
+  to:@1
+main: scope:[main]  from @1
+  (byte) ypos#10 ← phi( @1/(byte) ypos#9 )
+  (byte) counter#11 ← phi( @1/(byte) counter#10 )
+  to:main::@1
+main::@1: scope:[main]  from main main::@10 main::@6
+  (byte) ypos#8 ← phi( main/(byte) ypos#10 main::@10/(byte) ypos#1 main::@6/(byte) ypos#7 )
+  (byte) counter#9 ← phi( main/(byte) counter#11 main::@10/(byte) counter#2 main::@6/(byte) counter#1 )
+  if(true) goto main::@4
+  to:main::@return
+main::@4: scope:[main]  from main::@1 main::@4
+  (byte) ypos#11 ← phi( main::@1/(byte) ypos#8 main::@4/(byte) ypos#11 )
+  (byte) counter#8 ← phi( main::@1/(byte) counter#9 main::@4/(byte) counter#8 )
+  (bool~) main::$0 ← *((byte*) RASTER#0) != (number) $ff
+  if((bool~) main::$0) goto main::@4
+  to:main::@6
+main::@6: scope:[main]  from main::@4
+  (byte) ypos#7 ← phi( main::@4/(byte) ypos#11 )
+  (byte) counter#5 ← phi( main::@4/(byte) counter#8 )
+  (byte) counter#1 ← -- (byte) counter#5
+  (bool~) main::$1 ← (byte) counter#1 == (number) 0
+  (bool~) main::$2 ← ! (bool~) main::$1
+  if((bool~) main::$2) goto main::@1
+  to:main::@10
+main::@10: scope:[main]  from main::@6
+  (byte) ypos#4 ← phi( main::@6/(byte) ypos#7 )
+  (byte) counter#2 ← (byte) RATE#0
+  (byte) ypos#1 ← ++ (byte) ypos#4
+  *((byte*) SCREEN#0) ← (byte) ypos#1
+  to:main::@1
+main::@return: scope:[main]  from main::@1
+  (byte) ypos#5 ← phi( main::@1/(byte) ypos#8 )
+  (byte) counter#6 ← phi( main::@1/(byte) counter#9 )
+  (byte) counter#3 ← (byte) counter#6
+  (byte) ypos#2 ← (byte) ypos#5
+  return 
+  to:@return
+@1: scope:[]  from @begin
+  (byte) ypos#9 ← phi( @begin/(byte) ypos#0 )
+  (byte) counter#10 ← phi( @begin/(byte) counter#0 )
+  call main 
+  to:@2
+@2: scope:[]  from @1
+  (byte) ypos#6 ← phi( @1/(byte) ypos#2 )
+  (byte) counter#7 ← phi( @1/(byte) counter#3 )
+  (byte) counter#4 ← (byte) counter#7
+  (byte) ypos#3 ← (byte) ypos#6
+  to:@end
+@end: scope:[]  from @2
+
+SYMBOL TABLE SSA
+(label) @1
+(label) @2
+(label) @begin
+(label) @end
+(byte*) RASTER
+(byte*) RASTER#0
+(byte) RATE
+(byte) RATE#0
+(byte*) SCREEN
+(byte*) SCREEN#0
+(byte) counter
+(byte) counter#0
+(byte) counter#1
+(byte) counter#10
+(byte) counter#11
+(byte) counter#2
+(byte) counter#3
+(byte) counter#4
+(byte) counter#5
+(byte) counter#6
+(byte) counter#7
+(byte) counter#8
+(byte) counter#9
+(void()) main()
+(bool~) main::$0
+(bool~) main::$1
+(bool~) main::$2
+(label) main::@1
+(label) main::@10
+(label) main::@4
+(label) main::@6
+(label) main::@return
+(byte) ypos
+(byte) ypos#0
+(byte) ypos#1
+(byte) ypos#10
+(byte) ypos#11
+(byte) ypos#2
+(byte) ypos#3
+(byte) ypos#4
+(byte) ypos#5
+(byte) ypos#6
+(byte) ypos#7
+(byte) ypos#8
+(byte) ypos#9
+
+Adding number conversion cast (unumber) 0 in (byte) ypos#0 ← (number) 0
+Adding number conversion cast (unumber) $32 in (byte) RATE#0 ← (number) $32
+Adding number conversion cast (unumber) $ff in (bool~) main::$0 ← *((byte*) RASTER#0) != (number) $ff
+Adding number conversion cast (unumber) 0 in (bool~) main::$1 ← (byte) counter#1 == (number) 0
+Successful SSA optimization PassNAddNumberTypeConversions
+Inlining cast (byte*) RASTER#0 ← (byte*)(number) $d012
+Inlining cast (byte*) SCREEN#0 ← (byte*)(number) $400
+Inlining cast (byte) ypos#0 ← (unumber)(number) 0
+Inlining cast (byte) RATE#0 ← (unumber)(number) $32
+Successful SSA optimization Pass2InlineCast
+Simplifying constant pointer cast (byte*) 53266
+Simplifying constant pointer cast (byte*) 1024
+Simplifying constant integer cast 0
+Simplifying constant integer cast $32
+Simplifying constant integer cast $ff
+Simplifying constant integer cast 0
+Successful SSA optimization PassNCastSimplification
+Finalized unsigned number type (byte) 0
+Finalized unsigned number type (byte) $32
+Finalized unsigned number type (byte) $ff
+Finalized unsigned number type (byte) 0
+Successful SSA optimization PassNFinalizeNumberTypeConversions
+Inversing boolean not [14] (bool~) main::$2 ← (byte) counter#1 != (byte) 0 from [13] (bool~) main::$1 ← (byte) counter#1 == (byte) 0
+Successful SSA optimization Pass2UnaryNotSimplification
+Alias (byte) RATE#0 = (byte) counter#0 (byte) counter#10 
+Alias (byte) counter#5 = (byte) counter#8 
+Alias (byte) ypos#11 = (byte) ypos#7 (byte) ypos#4 
+Alias (byte) counter#3 = (byte) counter#6 (byte) counter#9 
+Alias (byte) ypos#2 = (byte) ypos#5 (byte) ypos#8 
+Alias (byte) ypos#0 = (byte) ypos#9 
+Alias (byte) counter#4 = (byte) counter#7 
+Alias (byte) ypos#3 = (byte) ypos#6 
+Successful SSA optimization Pass2AliasElimination
+Self Phi Eliminated (byte) counter#5
+Self Phi Eliminated (byte) ypos#11
+Successful SSA optimization Pass2SelfPhiElimination
+Identical Phi Values (byte) counter#11 (byte) RATE#0
+Identical Phi Values (byte) ypos#10 (byte) ypos#0
+Identical Phi Values (byte) counter#5 (byte) counter#3
+Identical Phi Values (byte) ypos#11 (byte) ypos#2
+Identical Phi Values (byte) counter#4 (byte) counter#3
+Identical Phi Values (byte) ypos#3 (byte) ypos#2
+Successful SSA optimization Pass2IdenticalPhiElimination
+Simple Condition (bool~) main::$0 [10] if(*((byte*) RASTER#0)!=(byte) $ff) goto main::@4
+Simple Condition (bool~) main::$2 [15] if((byte) counter#1!=(byte) 0) goto main::@1
+Successful SSA optimization Pass2ConditionalJumpSimplification
+Constant (const byte*) RASTER#0 = (byte*) 53266
+Constant (const byte*) SCREEN#0 = (byte*) 1024
+Constant (const byte) ypos#0 = 0
+Constant (const byte) RATE#0 = $32
+Successful SSA optimization Pass2ConstantIdentification
+Constant (const byte) counter#2 = RATE#0
+Successful SSA optimization Pass2ConstantIdentification
+if() condition always true - replacing block destination [7] if(true) goto main::@4
+Successful SSA optimization Pass2ConstantIfs
+Removing unused block main::@return
+Successful SSA optimization Pass2EliminateUnusedBlocks
+Self Phi Eliminated (byte) ypos#2
+Successful SSA optimization Pass2SelfPhiElimination
+Inlining constant with var siblings (const byte) ypos#0
+Inlining constant with var siblings (const byte) counter#2
+Constant inlined ypos#0 = (byte) 0
+Constant inlined counter#2 = (const byte) RATE#0
+Successful SSA optimization Pass2ConstantInlining
+Added new block during phi lifting main::@15(between main::@6 and main::@1)
+Adding NOP phi() at start of @begin
+Adding NOP phi() at start of @1
+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 
+
+Created 2 initial phi equivalence classes
+Coalesced [12] ypos#12 ← ypos#1
+Coalesced [13] counter#12 ← counter#1
+Coalesced down to 2 phi equivalence classes
+Culled Empty Block (label) @2
+Culled Empty Block (label) main::@15
+Renumbering block main::@4 to main::@2
+Renumbering block main::@6 to main::@3
+Renumbering block main::@10 to main::@4
+Adding NOP phi() at start of @begin
+Adding NOP phi() at start of @1
+Adding NOP phi() at start of @end
+Adding NOP phi() at start of main
+
+FINAL CONTROL FLOW GRAPH
+@begin: scope:[]  from
+  [0] phi()
+  to:@1
+@1: scope:[]  from @begin
+  [1] phi()
+  [2] call main 
+  to:@end
+@end: scope:[]  from @1
+  [3] phi()
+main: scope:[main]  from @1
+  [4] phi()
+  to:main::@1
+main::@1: scope:[main]  from main main::@3 main::@4
+  [5] (byte) ypos#2 ← phi( main/(byte) 0 main::@4/(byte) ypos#1 )
+  [5] (byte) counter#3 ← phi( main/(const byte) RATE#0 main::@4/(const byte) RATE#0 main::@3/(byte) counter#1 )
+  to:main::@2
+main::@2: scope:[main]  from main::@1 main::@2
+  [6] if(*((const byte*) RASTER#0)!=(byte) $ff) goto main::@2
+  to:main::@3
+main::@3: scope:[main]  from main::@2
+  [7] (byte) counter#1 ← -- (byte) counter#3
+  [8] if((byte) counter#1!=(byte) 0) goto main::@1
+  to:main::@4
+main::@4: scope:[main]  from main::@3
+  [9] (byte) ypos#1 ← ++ (byte) ypos#2
+  [10] *((const byte*) SCREEN#0) ← (byte) ypos#1
+  to:main::@1
+
+
+VARIABLE REGISTER WEIGHTS
+(byte*) RASTER
+(byte) RATE
+(byte*) SCREEN
+(byte) counter
+(byte) counter#1 151.5
+(byte) counter#3 101.0
+(void()) main()
+(byte) ypos
+(byte) ypos#1 16.5
+(byte) ypos#2 5.5
+
+Initial phi equivalence classes
+[ counter#3 counter#1 ]
+[ ypos#2 ypos#1 ]
+Complete equivalence classes
+[ counter#3 counter#1 ]
+[ ypos#2 ypos#1 ]
+Allocated zp ZP_BYTE:2 [ counter#3 counter#1 ]
+Allocated zp ZP_BYTE:3 [ ypos#2 ypos#1 ]
+
+INITIAL ASM
+//SEG0 File Comments
+// NullPointerException using current_movedown_rate in the main loop
+//SEG1 Basic Upstart
+.pc = $801 "Basic"
+:BasicUpstart(bbegin)
+.pc = $80d "Program"
+//SEG2 Global Constants & labels
+  .label RASTER = $d012
+  .label SCREEN = $400
+  .const RATE = $32
+  .label counter = 2
+  .label ypos = 3
+//SEG3 @begin
+bbegin:
+//SEG4 [1] phi from @begin to @1 [phi:@begin->@1]
+b1_from_bbegin:
+  jmp b1
+//SEG5 @1
+b1:
+//SEG6 [2] call main 
+//SEG7 [4] phi from @1 to main [phi:@1->main]
+main_from_b1:
+  jsr main
+//SEG8 [3] phi from @1 to @end [phi:@1->@end]
+bend_from_b1:
+  jmp bend
+//SEG9 @end
+bend:
+//SEG10 main
+main: {
+  //SEG11 [5] phi from main to main::@1 [phi:main->main::@1]
+  b1_from_main:
+  //SEG12 [5] phi (byte) ypos#2 = (byte) 0 [phi:main->main::@1#0] -- vbuz1=vbuc1 
+    lda #0
+    sta ypos
+  //SEG13 [5] phi (byte) counter#3 = (const byte) RATE#0 [phi:main->main::@1#1] -- vbuz1=vbuc1 
+    lda #RATE
+    sta counter
+    jmp b1
+  //SEG14 [5] phi from main::@3 to main::@1 [phi:main::@3->main::@1]
+  b1_from_b3:
+  //SEG15 [5] phi (byte) counter#3 = (byte) counter#1 [phi:main::@3->main::@1#0] -- register_copy 
+    jmp b1
+  //SEG16 main::@1
+  b1:
+    jmp b2
+  //SEG17 main::@2
+  b2:
+  //SEG18 [6] if(*((const byte*) RASTER#0)!=(byte) $ff) goto main::@2 -- _deref_pbuc1_neq_vbuc2_then_la1 
+    lda #$ff
+    cmp RASTER
+    bne b2
+    jmp b3
+  //SEG19 main::@3
+  b3:
+  //SEG20 [7] (byte) counter#1 ← -- (byte) counter#3 -- vbuz1=_dec_vbuz1 
+    dec counter
+  //SEG21 [8] if((byte) counter#1!=(byte) 0) goto main::@1 -- vbuz1_neq_0_then_la1 
+    lda counter
+    cmp #0
+    bne b1_from_b3
+    jmp b4
+  //SEG22 main::@4
+  b4:
+  //SEG23 [9] (byte) ypos#1 ← ++ (byte) ypos#2 -- vbuz1=_inc_vbuz1 
+    inc ypos
+  //SEG24 [10] *((const byte*) SCREEN#0) ← (byte) ypos#1 -- _deref_pbuc1=vbuz1 
+    lda ypos
+    sta SCREEN
+  //SEG25 [5] phi from main::@4 to main::@1 [phi:main::@4->main::@1]
+  b1_from_b4:
+  //SEG26 [5] phi (byte) ypos#2 = (byte) ypos#1 [phi:main::@4->main::@1#0] -- register_copy 
+  //SEG27 [5] phi (byte) counter#3 = (const byte) RATE#0 [phi:main::@4->main::@1#1] -- vbuz1=vbuc1 
+    lda #RATE
+    sta counter
+    jmp b1
+}
+//SEG28 File Data
+
+REGISTER UPLIFT POTENTIAL REGISTERS
+Statement [6] if(*((const byte*) RASTER#0)!=(byte) $ff) goto main::@2 [ counter#3 ypos#2 ] ( main:2 [ counter#3 ypos#2 ] ) always clobbers reg byte a 
+Removing always clobbered register reg byte a as potential for zp ZP_BYTE:2 [ counter#3 counter#1 ]
+Removing always clobbered register reg byte a as potential for zp ZP_BYTE:3 [ ypos#2 ypos#1 ]
+Statement [6] if(*((const byte*) RASTER#0)!=(byte) $ff) goto main::@2 [ counter#3 ypos#2 ] ( main:2 [ counter#3 ypos#2 ] ) always clobbers reg byte a 
+Potential registers zp ZP_BYTE:2 [ counter#3 counter#1 ] : zp ZP_BYTE:2 , reg byte x , reg byte y , 
+Potential registers zp ZP_BYTE:3 [ ypos#2 ypos#1 ] : zp ZP_BYTE:3 , reg byte x , reg byte y , 
+
+REGISTER UPLIFT SCOPES
+Uplift Scope [] 252.5: zp ZP_BYTE:2 [ counter#3 counter#1 ] 22: zp ZP_BYTE:3 [ ypos#2 ypos#1 ] 
+Uplift Scope [main] 
+
+Uplifting [] best 14052 combination reg byte y [ counter#3 counter#1 ] reg byte x [ ypos#2 ypos#1 ] 
+Uplifting [main] best 14052 combination 
+
+ASSEMBLER BEFORE OPTIMIZATION
+//SEG0 File Comments
+// NullPointerException using current_movedown_rate in the main loop
+//SEG1 Basic Upstart
+.pc = $801 "Basic"
+:BasicUpstart(bbegin)
+.pc = $80d "Program"
+//SEG2 Global Constants & labels
+  .label RASTER = $d012
+  .label SCREEN = $400
+  .const RATE = $32
+//SEG3 @begin
+bbegin:
+//SEG4 [1] phi from @begin to @1 [phi:@begin->@1]
+b1_from_bbegin:
+  jmp b1
+//SEG5 @1
+b1:
+//SEG6 [2] call main 
+//SEG7 [4] phi from @1 to main [phi:@1->main]
+main_from_b1:
+  jsr main
+//SEG8 [3] phi from @1 to @end [phi:@1->@end]
+bend_from_b1:
+  jmp bend
+//SEG9 @end
+bend:
+//SEG10 main
+main: {
+  //SEG11 [5] phi from main to main::@1 [phi:main->main::@1]
+  b1_from_main:
+  //SEG12 [5] phi (byte) ypos#2 = (byte) 0 [phi:main->main::@1#0] -- vbuxx=vbuc1 
+    ldx #0
+  //SEG13 [5] phi (byte) counter#3 = (const byte) RATE#0 [phi:main->main::@1#1] -- vbuyy=vbuc1 
+    ldy #RATE
+    jmp b1
+  //SEG14 [5] phi from main::@3 to main::@1 [phi:main::@3->main::@1]
+  b1_from_b3:
+  //SEG15 [5] phi (byte) counter#3 = (byte) counter#1 [phi:main::@3->main::@1#0] -- register_copy 
+    jmp b1
+  //SEG16 main::@1
+  b1:
+    jmp b2
+  //SEG17 main::@2
+  b2:
+  //SEG18 [6] if(*((const byte*) RASTER#0)!=(byte) $ff) goto main::@2 -- _deref_pbuc1_neq_vbuc2_then_la1 
+    lda #$ff
+    cmp RASTER
+    bne b2
+    jmp b3
+  //SEG19 main::@3
+  b3:
+  //SEG20 [7] (byte) counter#1 ← -- (byte) counter#3 -- vbuyy=_dec_vbuyy 
+    dey
+  //SEG21 [8] if((byte) counter#1!=(byte) 0) goto main::@1 -- vbuyy_neq_0_then_la1 
+    cpy #0
+    bne b1_from_b3
+    jmp b4
+  //SEG22 main::@4
+  b4:
+  //SEG23 [9] (byte) ypos#1 ← ++ (byte) ypos#2 -- vbuxx=_inc_vbuxx 
+    inx
+  //SEG24 [10] *((const byte*) SCREEN#0) ← (byte) ypos#1 -- _deref_pbuc1=vbuxx 
+    stx SCREEN
+  //SEG25 [5] phi from main::@4 to main::@1 [phi:main::@4->main::@1]
+  b1_from_b4:
+  //SEG26 [5] phi (byte) ypos#2 = (byte) ypos#1 [phi:main::@4->main::@1#0] -- register_copy 
+  //SEG27 [5] phi (byte) counter#3 = (const byte) RATE#0 [phi:main::@4->main::@1#1] -- vbuyy=vbuc1 
+    ldy #RATE
+    jmp b1
+}
+//SEG28 File Data
+
+ASSEMBLER OPTIMIZATIONS
+Removing instruction jmp b1
+Removing instruction jmp bend
+Removing instruction jmp b1
+Removing instruction jmp b2
+Removing instruction jmp b3
+Removing instruction jmp b4
+Succesful ASM optimization Pass5NextJumpElimination
+Replacing label b1 with b2
+Replacing label b1_from_b3 with b2
+Replacing label b1 with b2
+Removing instruction b1_from_bbegin:
+Removing instruction b1:
+Removing instruction main_from_b1:
+Removing instruction bend_from_b1:
+Removing instruction b1_from_b3:
+Removing instruction b1:
+Succesful ASM optimization Pass5RedundantLabelElimination
+Removing instruction bend:
+Removing instruction b1_from_main:
+Removing instruction b3:
+Removing instruction b4:
+Removing instruction b1_from_b4:
+Succesful ASM optimization Pass5UnusedLabelElimination
+Updating BasicUpstart to call main directly
+Removing instruction jsr main
+Succesful ASM optimization Pass5SkipBegin
+Removing instruction jmp b2
+Succesful ASM optimization Pass5NextJumpElimination
+Removing instruction bbegin:
+Succesful ASM optimization Pass5UnusedLabelElimination
+
+FINAL SYMBOL TABLE
+(label) @1
+(label) @begin
+(label) @end
+(byte*) RASTER
+(const byte*) RASTER#0 RASTER = (byte*) 53266
+(byte) RATE
+(const byte) RATE#0 RATE = (byte) $32
+(byte*) SCREEN
+(const byte*) SCREEN#0 SCREEN = (byte*) 1024
+(byte) counter
+(byte) counter#1 reg byte y 151.5
+(byte) counter#3 reg byte y 101.0
+(void()) main()
+(label) main::@1
+(label) main::@2
+(label) main::@3
+(label) main::@4
+(byte) ypos
+(byte) ypos#1 reg byte x 16.5
+(byte) ypos#2 reg byte x 5.5
+
+reg byte y [ counter#3 counter#1 ]
+reg byte x [ ypos#2 ypos#1 ]
+
+
+FINAL ASSEMBLER
+Score: 10110
+
+//SEG0 File Comments
+// NullPointerException using current_movedown_rate in the main loop
+//SEG1 Basic Upstart
+.pc = $801 "Basic"
+:BasicUpstart(main)
+.pc = $80d "Program"
+//SEG2 Global Constants & labels
+  .label RASTER = $d012
+  .label SCREEN = $400
+  .const RATE = $32
+//SEG3 @begin
+//SEG4 [1] phi from @begin to @1 [phi:@begin->@1]
+//SEG5 @1
+//SEG6 [2] call main 
+//SEG7 [4] phi from @1 to main [phi:@1->main]
+//SEG8 [3] phi from @1 to @end [phi:@1->@end]
+//SEG9 @end
+//SEG10 main
+main: {
+  //SEG11 [5] phi from main to main::@1 [phi:main->main::@1]
+  //SEG12 [5] phi (byte) ypos#2 = (byte) 0 [phi:main->main::@1#0] -- vbuxx=vbuc1 
+    ldx #0
+  //SEG13 [5] phi (byte) counter#3 = (const byte) RATE#0 [phi:main->main::@1#1] -- vbuyy=vbuc1 
+    ldy #RATE
+  //SEG14 [5] phi from main::@3 to main::@1 [phi:main::@3->main::@1]
+  //SEG15 [5] phi (byte) counter#3 = (byte) counter#1 [phi:main::@3->main::@1#0] -- register_copy 
+  //SEG16 main::@1
+  //SEG17 main::@2
+  b2:
+  //SEG18 [6] if(*((const byte*) RASTER#0)!=(byte) $ff) goto main::@2 -- _deref_pbuc1_neq_vbuc2_then_la1 
+    lda #$ff
+    cmp RASTER
+    bne b2
+  //SEG19 main::@3
+  //SEG20 [7] (byte) counter#1 ← -- (byte) counter#3 -- vbuyy=_dec_vbuyy 
+    dey
+  //SEG21 [8] if((byte) counter#1!=(byte) 0) goto main::@1 -- vbuyy_neq_0_then_la1 
+    cpy #0
+    bne b2
+  //SEG22 main::@4
+  //SEG23 [9] (byte) ypos#1 ← ++ (byte) ypos#2 -- vbuxx=_inc_vbuxx 
+    inx
+  //SEG24 [10] *((const byte*) SCREEN#0) ← (byte) ypos#1 -- _deref_pbuc1=vbuxx 
+    stx SCREEN
+  //SEG25 [5] phi from main::@4 to main::@1 [phi:main::@4->main::@1]
+  //SEG26 [5] phi (byte) ypos#2 = (byte) ypos#1 [phi:main::@4->main::@1#0] -- register_copy 
+  //SEG27 [5] phi (byte) counter#3 = (const byte) RATE#0 [phi:main::@4->main::@1#1] -- vbuyy=vbuc1 
+    ldy #RATE
+    jmp b2
+}
+//SEG28 File Data
+
diff --git a/src/test/ref/tetris-npe.sym b/src/test/ref/tetris-npe.sym
new file mode 100644
index 000000000..74bde72be
--- /dev/null
+++ b/src/test/ref/tetris-npe.sym
@@ -0,0 +1,23 @@
+(label) @1
+(label) @begin
+(label) @end
+(byte*) RASTER
+(const byte*) RASTER#0 RASTER = (byte*) 53266
+(byte) RATE
+(const byte) RATE#0 RATE = (byte) $32
+(byte*) SCREEN
+(const byte*) SCREEN#0 SCREEN = (byte*) 1024
+(byte) counter
+(byte) counter#1 reg byte y 151.5
+(byte) counter#3 reg byte y 101.0
+(void()) main()
+(label) main::@1
+(label) main::@2
+(label) main::@3
+(label) main::@4
+(byte) ypos
+(byte) ypos#1 reg byte x 16.5
+(byte) ypos#2 reg byte x 5.5
+
+reg byte y [ counter#3 counter#1 ]
+reg byte x [ ypos#2 ypos#1 ]