From 1f133e34e9e85b2548c11a6d4f94d52c282104d3 Mon Sep 17 00:00:00 2001
From: jespergravgaard <jesper@balmangravgaard.dk>
Date: Tue, 17 Aug 2021 07:48:58 +0200
Subject: [PATCH] Added very naive support for zeropage overflow to main memory
 upon exhaust. TODO - overflow low priority variables. #712

---
 .../kickc/passes/Pass4CodeGeneration.java     |  14 +-
 .../kickc/passes/Pass4RegistersFinalize.java  |   7 +
 .../kickc/test/TestProgramsFast.java          |   7 +-
 src/test/kc/zeropage-overflow.c               |  25 +
 src/test/ref/zeropage-exhausted.asm           |  47 +
 src/test/ref/zeropage-exhausted.cfg           |  18 +
 src/test/ref/zeropage-exhausted.log           | 302 +++++++
 src/test/ref/zeropage-exhausted.sym           |  11 +
 src/test/ref/zeropage-overflow.asm            | 134 +++
 src/test/ref/zeropage-overflow.cfg            |  40 +
 src/test/ref/zeropage-overflow.log            | 816 ++++++++++++++++++
 src/test/ref/zeropage-overflow.sym            |  41 +
 12 files changed, 1451 insertions(+), 11 deletions(-)
 create mode 100644 src/test/kc/zeropage-overflow.c
 create mode 100644 src/test/ref/zeropage-exhausted.asm
 create mode 100644 src/test/ref/zeropage-exhausted.cfg
 create mode 100644 src/test/ref/zeropage-exhausted.log
 create mode 100644 src/test/ref/zeropage-exhausted.sym
 create mode 100644 src/test/ref/zeropage-overflow.asm
 create mode 100644 src/test/ref/zeropage-overflow.cfg
 create mode 100644 src/test/ref/zeropage-overflow.log
 create mode 100644 src/test/ref/zeropage-overflow.sym

diff --git a/src/main/java/dk/camelot64/kickc/passes/Pass4CodeGeneration.java b/src/main/java/dk/camelot64/kickc/passes/Pass4CodeGeneration.java
index dbc724880..0ddf869ce 100644
--- a/src/main/java/dk/camelot64/kickc/passes/Pass4CodeGeneration.java
+++ b/src/main/java/dk/camelot64/kickc/passes/Pass4CodeGeneration.java
@@ -564,22 +564,16 @@ public class Pass4CodeGeneration {
       // Add all memory variables
       Collection<Variable> scopeVariables = scope.getAllVariables(false);
       for(Variable variable : scopeVariables) {
-         if(variable.isMemoryAreaMain()) {
+         Registers.Register allocation = variable.getAllocation();
+         if(variable.getAllocation() instanceof Registers.RegisterMainMem) {
+            Registers.RegisterMainMem registerMainMem = (Registers.RegisterMainMem) allocation;
             // Skip PHI masters
             if(variable.isKindPhiMaster())
                continue;
             // Skip if already added
-            if(added.contains(variable.getAsmName())) {
+            if(added.contains(variable.getAsmName()))
                continue;
-            }
             if(variable.isKindLoadStore() || variable.isKindPhiVersion() || variable.isKindIntermediate()) {
-               Registers.Register allocation = variable.getAllocation();
-               if(allocation instanceof Registers.RegisterCpuByte)
-                  continue;
-               if(!(allocation instanceof Registers.RegisterMainMem)) {
-                  throw new InternalError("Expected main memory allocation " + variable.toString(program));
-               }
-               Registers.RegisterMainMem registerMainMem = (Registers.RegisterMainMem) allocation;
                final Variable mainVar = program.getScope().getVariable(registerMainMem.getVariableRef());
                if(registerMainMem.getAddress() == null) {
                   // Generate into the data segment
diff --git a/src/main/java/dk/camelot64/kickc/passes/Pass4RegistersFinalize.java b/src/main/java/dk/camelot64/kickc/passes/Pass4RegistersFinalize.java
index 72f2a6925..52101339c 100644
--- a/src/main/java/dk/camelot64/kickc/passes/Pass4RegistersFinalize.java
+++ b/src/main/java/dk/camelot64/kickc/passes/Pass4RegistersFinalize.java
@@ -175,6 +175,13 @@ public class Pass4RegistersFinalize extends Pass2Base {
                register = new Registers.RegisterMainMem(variableRef, variable.getType().getSizeBytes(), null);
             }  else {
                register = allocateNewRegisterZp(variable);
+               int zp = ((Registers.RegisterZpMem) register).getZp();
+               int sizeBytes = variable.getType().getSizeBytes();
+               if(zp + sizeBytes > 0x100) {
+                  // Zero-page exhausted - move to main memory instead (TODO: prioritize!)
+                  register = new Registers.RegisterMainMem(variableRef, variable.getType().getSizeBytes(), null);
+                  getLog().append("Zero-page exhausted. Moving allocation to main memory "+variable.toString());
+               }
             }
             equivalenceClass.setRegister(register);
             if(before == null || !before.equals(register.toString())) {
diff --git a/src/test/java/dk/camelot64/kickc/test/TestProgramsFast.java b/src/test/java/dk/camelot64/kickc/test/TestProgramsFast.java
index c7760f1d8..84fc6eded 100644
--- a/src/test/java/dk/camelot64/kickc/test/TestProgramsFast.java
+++ b/src/test/java/dk/camelot64/kickc/test/TestProgramsFast.java
@@ -1816,9 +1816,14 @@ public class TestProgramsFast extends TestPrograms {
       compileAndCompare("array-16bit-lookup.c");
    }
 
+   @Test
+   public void testZeropageOverflow() throws IOException {
+      compileAndCompare("zeropage-overflow.c");
+   }
+
    @Test
    public void testZeropageExhausted() throws IOException {
-      assertError("zeropage-exhausted.c", "Variables used in program do not fit on zeropage", false);
+      compileAndCompare("zeropage-exhausted.c");
    }
 
    @Test
diff --git a/src/test/kc/zeropage-overflow.c b/src/test/kc/zeropage-overflow.c
new file mode 100644
index 000000000..cd696071a
--- /dev/null
+++ b/src/test/kc/zeropage-overflow.c
@@ -0,0 +1,25 @@
+// Tests that variables overflow to main memory when zeropage is exhausted
+
+// Tell the compiler to use zeropage
+#pragma var_model(ssa_zp)
+
+// Start by reserving most of zeropage (254 bytes)
+#pragma zp_reserve(1..250)
+
+// And then allocate a bunch of variables
+void main() {
+    int* const SCREEN = (int*)0x0400;
+
+    int a, b, c, d, e, f, g, h;
+
+    for(char i=0;i<10;i++) {
+        SCREEN[i] = a++;
+        SCREEN[i] = b++;
+        SCREEN[i] = c++;
+        SCREEN[i] = d++;
+        SCREEN[i] = e++;
+        SCREEN[i] = f++;
+        SCREEN[i] = g++;
+        SCREEN[i] = h++;
+    }
+}
diff --git a/src/test/ref/zeropage-exhausted.asm b/src/test/ref/zeropage-exhausted.asm
new file mode 100644
index 000000000..16598cf23
--- /dev/null
+++ b/src/test/ref/zeropage-exhausted.asm
@@ -0,0 +1,47 @@
+// Tests warning when running out of zeropage-addresses for variables
+  // Commodore 64 PRG executable file
+.file [name="zeropage-exhausted.prg", type="prg", segments="Program"]
+.segmentdef Program [segments="Basic, Code, Data"]
+.segmentdef Basic [start=$0801]
+.segmentdef Code [start=$80d]
+.segmentdef Data [startAfter="Code"]
+.segment Basic
+:BasicUpstart(main)
+.segment Code
+// And then allocate a 2-byte-variable
+main: {
+    .label SCREEN = $400
+    lda #<0
+    sta i
+    sta i+1
+  __b1:
+    // for(__zp int i=0;i<10;i++)
+    lda i+1
+    bmi __b2
+    cmp #>$a
+    bcc __b2
+    bne !+
+    lda i
+    cmp #<$a
+    bcc __b2
+  !:
+    // }
+    rts
+  __b2:
+    // SCREEN[(char)i] = i
+    lda i
+    asl
+    tay
+    lda i
+    sta SCREEN,y
+    lda i+1
+    sta SCREEN+1,y
+    // for(__zp int i=0;i<10;i++)
+    inc i
+    bne !+
+    inc i+1
+  !:
+    jmp __b1
+  .segment Data
+    i: .word 0
+}
diff --git a/src/test/ref/zeropage-exhausted.cfg b/src/test/ref/zeropage-exhausted.cfg
new file mode 100644
index 000000000..49cd3a601
--- /dev/null
+++ b/src/test/ref/zeropage-exhausted.cfg
@@ -0,0 +1,18 @@
+
+void main()
+main: scope:[main]  from
+  [0] phi()
+  to:main::@1
+main::@1: scope:[main]  from main main::@2
+  [1] main::i#2 = phi( main/0, main::@2/main::i#1 )
+  [2] if(main::i#2<$a) goto main::@2
+  to:main::@return
+main::@return: scope:[main]  from main::@1
+  [3] return 
+  to:@return
+main::@2: scope:[main]  from main::@1
+  [4] main::$2 = (char)main::i#2
+  [5] main::$1 = main::$2 << 1
+  [6] main::SCREEN[main::$1] = main::i#2
+  [7] main::i#1 = ++ main::i#2
+  to:main::@1
diff --git a/src/test/ref/zeropage-exhausted.log b/src/test/ref/zeropage-exhausted.log
new file mode 100644
index 000000000..f5298f246
--- /dev/null
+++ b/src/test/ref/zeropage-exhausted.log
@@ -0,0 +1,302 @@
+
+CONTROL FLOW GRAPH SSA
+
+void main()
+main: scope:[main]  from __start
+  main::i#0 = 0
+  to:main::@1
+main::@1: scope:[main]  from main main::@2
+  main::i#2 = phi( main/main::i#0, main::@2/main::i#1 )
+  main::$0 = main::i#2 < $a
+  if(main::$0) goto main::@2
+  to:main::@return
+main::@2: scope:[main]  from main::@1
+  main::i#3 = phi( main::@1/main::i#2 )
+  main::$2 = (char)main::i#3
+  main::$1 = main::$2 * SIZEOF_INT
+  main::SCREEN[main::$1] = main::i#3
+  main::i#1 = ++ main::i#3
+  to:main::@1
+main::@return: scope:[main]  from main::@1
+  return 
+  to:@return
+
+void __start()
+__start: scope:[__start]  from
+  call main
+  to:__start::@1
+__start::@1: scope:[__start]  from __start
+  to:__start::@return
+__start::@return: scope:[__start]  from __start::@1
+  return 
+  to:@return
+
+SYMBOL TABLE SSA
+__constant char SIZEOF_INT = 2
+void __start()
+void main()
+bool main::$0
+char main::$1
+char main::$2
+__constant int * const main::SCREEN = (int *)$400
+int main::i
+int main::i#0
+int main::i#1
+int main::i#2
+int main::i#3
+
+Adding number conversion cast (snumber) $a in main::$0 = main::i#2 < $a
+Successful SSA optimization PassNAddNumberTypeConversions
+Simplifying constant pointer cast (int *) 1024
+Simplifying constant integer cast $a
+Successful SSA optimization PassNCastSimplification
+Finalized signed number type (signed char) $a
+Successful SSA optimization PassNFinalizeNumberTypeConversions
+Alias main::i#2 = main::i#3 
+Successful SSA optimization Pass2AliasElimination
+Simple Condition main::$0 [3] if(main::i#2<$a) goto main::@2
+Successful SSA optimization Pass2ConditionalJumpSimplification
+Constant main::i#0 = 0
+Successful SSA optimization Pass2ConstantIdentification
+Removing unused procedure __start
+Removing unused procedure block __start
+Removing unused procedure block __start::@1
+Removing unused procedure block __start::@return
+Successful SSA optimization PassNEliminateEmptyStart
+Rewriting multiplication to use shift [3] main::$1 = main::$2 * SIZEOF_INT
+Successful SSA optimization Pass2MultiplyToShiftRewriting
+Inlining constant with var siblings main::i#0
+Constant inlined main::i#0 = 0
+Successful SSA optimization Pass2ConstantInlining
+Eliminating unused constant SIZEOF_INT
+Successful SSA optimization PassNEliminateUnusedVars
+Adding NOP phi() at start of main
+CALL GRAPH
+
+Created 1 initial phi equivalence classes
+Coalesced [8] main::i#4 = main::i#1
+Coalesced down to 1 phi equivalence classes
+Adding NOP phi() at start of main
+
+FINAL CONTROL FLOW GRAPH
+
+void main()
+main: scope:[main]  from
+  [0] phi()
+  to:main::@1
+main::@1: scope:[main]  from main main::@2
+  [1] main::i#2 = phi( main/0, main::@2/main::i#1 )
+  [2] if(main::i#2<$a) goto main::@2
+  to:main::@return
+main::@return: scope:[main]  from main::@1
+  [3] return 
+  to:@return
+main::@2: scope:[main]  from main::@1
+  [4] main::$2 = (char)main::i#2
+  [5] main::$1 = main::$2 << 1
+  [6] main::SCREEN[main::$1] = main::i#2
+  [7] main::i#1 = ++ main::i#2
+  to:main::@1
+
+
+VARIABLE REGISTER WEIGHTS
+void main()
+char main::$1 // 22.0
+char main::$2 // 22.0
+int main::i
+int main::i#1 // 22.0
+int main::i#2 // 8.8
+
+Initial phi equivalence classes
+[ main::i#2 main::i#1 ]
+Added variable main::$2 to live range equivalence class [ main::$2 ]
+Added variable main::$1 to live range equivalence class [ main::$1 ]
+Complete equivalence classes
+[ main::i#2 main::i#1 ]
+[ main::$2 ]
+[ main::$1 ]
+Zero-page exhausted. Moving allocation to main memory main::i#2
+Allocated mem[2] [ main::i#2 main::i#1 ]
+Zero-page exhausted. Moving allocation to main memory main::$2
+Allocated mem[1] [ main::$2 ]
+Zero-page exhausted. Moving allocation to main memory main::$1
+Allocated mem[1] [ main::$1 ]
+REGISTER UPLIFT POTENTIAL REGISTERS
+Statement [2] if(main::i#2<$a) goto main::@2 [ main::i#2 ] (  [ main::i#2 ] { }  ) always clobbers reg byte a 
+Statement [4] main::$2 = (char)main::i#2 [ main::i#2 main::$2 ] (  [ main::i#2 main::$2 ] { }  ) always clobbers reg byte a 
+Statement [5] main::$1 = main::$2 << 1 [ main::i#2 main::$1 ] (  [ main::i#2 main::$1 ] { }  ) always clobbers reg byte a 
+Statement [6] main::SCREEN[main::$1] = main::i#2 [ main::i#2 ] (  [ main::i#2 ] { }  ) always clobbers reg byte a 
+Potential registers mem[2] [ main::i#2 main::i#1 ] : mem[2] , 
+Potential registers mem[1] [ main::$2 ] : mem[1] , reg byte a , reg byte x , reg byte y , 
+Potential registers mem[1] [ main::$1 ] : mem[1] , reg byte a , reg byte x , reg byte y , 
+
+REGISTER UPLIFT SCOPES
+Uplift Scope [main] 30.8: mem[2] [ main::i#2 main::i#1 ] 22: mem[1] [ main::$2 ] 22: mem[1] [ main::$1 ] 
+Uplift Scope [] 
+
+Uplifting [main] best 841 combination mem[2] [ main::i#2 main::i#1 ] reg byte a [ main::$2 ] reg byte a [ main::$1 ] 
+Uplifting [] best 841 combination 
+
+ASSEMBLER BEFORE OPTIMIZATION
+  // File Comments
+// Tests warning when running out of zeropage-addresses for variables
+  // Upstart
+  // Commodore 64 PRG executable file
+.file [name="zeropage-exhausted.prg", type="prg", segments="Program"]
+.segmentdef Program [segments="Basic, Code, Data"]
+.segmentdef Basic [start=$0801]
+.segmentdef Code [start=$80d]
+.segmentdef Data [startAfter="Code"]
+.segment Basic
+:BasicUpstart(main)
+  // Global Constants & labels
+.segment Code
+  // main
+// And then allocate a 2-byte-variable
+main: {
+    .label SCREEN = $400
+    // [1] phi from main to main::@1 [phi:main->main::@1]
+  __b1_from_main:
+    // [1] phi main::i#2 = 0 [phi:main->main::@1#0] -- vwsm1=vwsc1 
+    lda #<0
+    sta i
+    lda #>0
+    sta i+1
+    jmp __b1
+    // main::@1
+  __b1:
+    // [2] if(main::i#2<$a) goto main::@2 -- vwsm1_lt_vwuc1_then_la1 
+    lda i+1
+    bmi __b2
+    cmp #>$a
+    bcc __b2
+    bne !+
+    lda i
+    cmp #<$a
+    bcc __b2
+  !:
+    jmp __breturn
+    // main::@return
+  __breturn:
+    // [3] return 
+    rts
+    // main::@2
+  __b2:
+    // [4] main::$2 = (char)main::i#2 -- vbuaa=_byte_vwsm1 
+    lda i
+    // [5] main::$1 = main::$2 << 1 -- vbuaa=vbuaa_rol_1 
+    asl
+    // [6] main::SCREEN[main::$1] = main::i#2 -- pwsc1_derefidx_vbuaa=vwsm1 
+    tay
+    lda i
+    sta SCREEN,y
+    lda i+1
+    sta SCREEN+1,y
+    // [7] main::i#1 = ++ main::i#2 -- vwsm1=_inc_vwsm1 
+    inc i
+    bne !+
+    inc i+1
+  !:
+    // [1] phi from main::@2 to main::@1 [phi:main::@2->main::@1]
+  __b1_from___b2:
+    // [1] phi main::i#2 = main::i#1 [phi:main::@2->main::@1#0] -- register_copy 
+    jmp __b1
+  .segment Data
+    i: .word 0
+}
+  // File Data
+
+ASSEMBLER OPTIMIZATIONS
+Removing instruction jmp __b1
+Removing instruction jmp __breturn
+Succesful ASM optimization Pass5NextJumpElimination
+Removing instruction lda #>0
+Succesful ASM optimization Pass5UnnecesaryLoadElimination
+Removing instruction __b1_from_main:
+Removing instruction __breturn:
+Removing instruction __b1_from___b2:
+Succesful ASM optimization Pass5UnusedLabelElimination
+
+FINAL SYMBOL TABLE
+void main()
+char main::$1 // reg byte a 22.0
+char main::$2 // reg byte a 22.0
+__constant int * const main::SCREEN = (int *) 1024
+int main::i
+int main::i#1 // i mem[2] 22.0
+int main::i#2 // i mem[2] 8.8
+
+mem[2] [ main::i#2 main::i#1 ]
+reg byte a [ main::$2 ]
+reg byte a [ main::$1 ]
+
+
+FINAL ASSEMBLER
+Score: 761
+
+  // File Comments
+// Tests warning when running out of zeropage-addresses for variables
+  // Upstart
+  // Commodore 64 PRG executable file
+.file [name="zeropage-exhausted.prg", type="prg", segments="Program"]
+.segmentdef Program [segments="Basic, Code, Data"]
+.segmentdef Basic [start=$0801]
+.segmentdef Code [start=$80d]
+.segmentdef Data [startAfter="Code"]
+.segment Basic
+:BasicUpstart(main)
+  // Global Constants & labels
+.segment Code
+  // main
+// And then allocate a 2-byte-variable
+main: {
+    .label SCREEN = $400
+    // [1] phi from main to main::@1 [phi:main->main::@1]
+    // [1] phi main::i#2 = 0 [phi:main->main::@1#0] -- vwsm1=vwsc1 
+    lda #<0
+    sta i
+    sta i+1
+    // main::@1
+  __b1:
+    // for(__zp int i=0;i<10;i++)
+    // [2] if(main::i#2<$a) goto main::@2 -- vwsm1_lt_vwuc1_then_la1 
+    lda i+1
+    bmi __b2
+    cmp #>$a
+    bcc __b2
+    bne !+
+    lda i
+    cmp #<$a
+    bcc __b2
+  !:
+    // main::@return
+    // }
+    // [3] return 
+    rts
+    // main::@2
+  __b2:
+    // SCREEN[(char)i] = i
+    // [4] main::$2 = (char)main::i#2 -- vbuaa=_byte_vwsm1 
+    lda i
+    // [5] main::$1 = main::$2 << 1 -- vbuaa=vbuaa_rol_1 
+    asl
+    // [6] main::SCREEN[main::$1] = main::i#2 -- pwsc1_derefidx_vbuaa=vwsm1 
+    tay
+    lda i
+    sta SCREEN,y
+    lda i+1
+    sta SCREEN+1,y
+    // for(__zp int i=0;i<10;i++)
+    // [7] main::i#1 = ++ main::i#2 -- vwsm1=_inc_vwsm1 
+    inc i
+    bne !+
+    inc i+1
+  !:
+    // [1] phi from main::@2 to main::@1 [phi:main::@2->main::@1]
+    // [1] phi main::i#2 = main::i#1 [phi:main::@2->main::@1#0] -- register_copy 
+    jmp __b1
+  .segment Data
+    i: .word 0
+}
+  // File Data
+
diff --git a/src/test/ref/zeropage-exhausted.sym b/src/test/ref/zeropage-exhausted.sym
new file mode 100644
index 000000000..1020a857f
--- /dev/null
+++ b/src/test/ref/zeropage-exhausted.sym
@@ -0,0 +1,11 @@
+void main()
+char main::$1 // reg byte a 22.0
+char main::$2 // reg byte a 22.0
+__constant int * const main::SCREEN = (int *) 1024
+int main::i
+int main::i#1 // i mem[2] 22.0
+int main::i#2 // i mem[2] 8.8
+
+mem[2] [ main::i#2 main::i#1 ]
+reg byte a [ main::$2 ]
+reg byte a [ main::$1 ]
diff --git a/src/test/ref/zeropage-overflow.asm b/src/test/ref/zeropage-overflow.asm
new file mode 100644
index 000000000..decd73b72
--- /dev/null
+++ b/src/test/ref/zeropage-overflow.asm
@@ -0,0 +1,134 @@
+// Tests that variables overflow to main memory when zeropage is exhausted
+  // Commodore 64 PRG executable file
+.file [name="zeropage-overflow.prg", type="prg", segments="Program"]
+.segmentdef Program [segments="Basic, Code, Data"]
+.segmentdef Basic [start=$0801]
+.segmentdef Code [start=$80d]
+.segmentdef Data [startAfter="Code"]
+.segment Basic
+:BasicUpstart(main)
+.segment Code
+// And then allocate a bunch of variables
+main: {
+    .label SCREEN = $400
+    .label a = $fb
+    .label b = $fd
+    lda #<0
+    sta h
+    sta h+1
+    sta g
+    sta g+1
+    sta f
+    sta f+1
+    sta e
+    sta e+1
+    sta d
+    sta d+1
+    sta c
+    sta c+1
+    sta.z b
+    sta.z b+1
+    sta.z a
+    sta.z a+1
+    tay
+  __b1:
+    // for(char i=0;i<10;i++)
+    cpy #$a
+    bcc __b2
+    // }
+    rts
+  __b2:
+    // SCREEN[i] = a++
+    tya
+    asl
+    tax
+    lda.z a
+    sta SCREEN,x
+    lda.z a+1
+    sta SCREEN+1,x
+    // SCREEN[i] = a++;
+    inc.z a
+    bne !+
+    inc.z a+1
+  !:
+    // SCREEN[i] = b++
+    lda.z b
+    sta SCREEN,x
+    lda.z b+1
+    sta SCREEN+1,x
+    // SCREEN[i] = b++;
+    inc.z b
+    bne !+
+    inc.z b+1
+  !:
+    // SCREEN[i] = c++
+    lda c
+    sta SCREEN,x
+    lda c+1
+    sta SCREEN+1,x
+    // SCREEN[i] = c++;
+    inc c
+    bne !+
+    inc c+1
+  !:
+    // SCREEN[i] = d++
+    lda d
+    sta SCREEN,x
+    lda d+1
+    sta SCREEN+1,x
+    // SCREEN[i] = d++;
+    inc d
+    bne !+
+    inc d+1
+  !:
+    // SCREEN[i] = e++
+    lda e
+    sta SCREEN,x
+    lda e+1
+    sta SCREEN+1,x
+    // SCREEN[i] = e++;
+    inc e
+    bne !+
+    inc e+1
+  !:
+    // SCREEN[i] = f++
+    lda f
+    sta SCREEN,x
+    lda f+1
+    sta SCREEN+1,x
+    // SCREEN[i] = f++;
+    inc f
+    bne !+
+    inc f+1
+  !:
+    // SCREEN[i] = g++
+    lda g
+    sta SCREEN,x
+    lda g+1
+    sta SCREEN+1,x
+    // SCREEN[i] = g++;
+    inc g
+    bne !+
+    inc g+1
+  !:
+    // SCREEN[i] = h++
+    lda h
+    sta SCREEN,x
+    lda h+1
+    sta SCREEN+1,x
+    // SCREEN[i] = h++;
+    inc h
+    bne !+
+    inc h+1
+  !:
+    // for(char i=0;i<10;i++)
+    iny
+    jmp __b1
+  .segment Data
+    c: .word 0
+    d: .word 0
+    e: .word 0
+    f: .word 0
+    g: .word 0
+    h: .word 0
+}
diff --git a/src/test/ref/zeropage-overflow.cfg b/src/test/ref/zeropage-overflow.cfg
new file mode 100644
index 000000000..148e880f1
--- /dev/null
+++ b/src/test/ref/zeropage-overflow.cfg
@@ -0,0 +1,40 @@
+
+void main()
+main: scope:[main]  from
+  [0] phi()
+  to:main::@1
+main::@1: scope:[main]  from main main::@2
+  [1] main::h#2 = phi( main/0, main::@2/main::h#1 )
+  [1] main::g#2 = phi( main/0, main::@2/main::g#1 )
+  [1] main::f#2 = phi( main/0, main::@2/main::f#1 )
+  [1] main::e#2 = phi( main/0, main::@2/main::e#1 )
+  [1] main::d#2 = phi( main/0, main::@2/main::d#1 )
+  [1] main::c#2 = phi( main/0, main::@2/main::c#1 )
+  [1] main::b#2 = phi( main/0, main::@2/main::b#1 )
+  [1] main::a#2 = phi( main/0, main::@2/main::a#1 )
+  [1] main::i#2 = phi( main/0, main::@2/main::i#1 )
+  [2] if(main::i#2<$a) goto main::@2
+  to:main::@return
+main::@return: scope:[main]  from main::@1
+  [3] return 
+  to:@return
+main::@2: scope:[main]  from main::@1
+  [4] main::$2 = main::i#2 << 1
+  [5] main::SCREEN[main::$2] = main::a#2
+  [6] main::a#1 = ++ main::a#2
+  [7] main::SCREEN[main::$2] = main::b#2
+  [8] main::b#1 = ++ main::b#2
+  [9] main::SCREEN[main::$2] = main::c#2
+  [10] main::c#1 = ++ main::c#2
+  [11] main::SCREEN[main::$2] = main::d#2
+  [12] main::d#1 = ++ main::d#2
+  [13] main::SCREEN[main::$2] = main::e#2
+  [14] main::e#1 = ++ main::e#2
+  [15] main::SCREEN[main::$2] = main::f#2
+  [16] main::f#1 = ++ main::f#2
+  [17] main::SCREEN[main::$2] = main::g#2
+  [18] main::g#1 = ++ main::g#2
+  [19] main::SCREEN[main::$2] = main::h#2
+  [20] main::h#1 = ++ main::h#2
+  [21] main::i#1 = ++ main::i#2
+  to:main::@1
diff --git a/src/test/ref/zeropage-overflow.log b/src/test/ref/zeropage-overflow.log
new file mode 100644
index 000000000..da7dea59e
--- /dev/null
+++ b/src/test/ref/zeropage-overflow.log
@@ -0,0 +1,816 @@
+
+CONTROL FLOW GRAPH SSA
+
+void main()
+main: scope:[main]  from __start
+  main::a#0 = 0
+  main::b#0 = 0
+  main::c#0 = 0
+  main::d#0 = 0
+  main::e#0 = 0
+  main::f#0 = 0
+  main::g#0 = 0
+  main::h#0 = 0
+  main::i#0 = 0
+  to:main::@1
+main::@1: scope:[main]  from main main::@2
+  main::h#3 = phi( main/main::h#0, main::@2/main::h#1 )
+  main::g#3 = phi( main/main::g#0, main::@2/main::g#1 )
+  main::f#3 = phi( main/main::f#0, main::@2/main::f#1 )
+  main::e#3 = phi( main/main::e#0, main::@2/main::e#1 )
+  main::d#3 = phi( main/main::d#0, main::@2/main::d#1 )
+  main::c#3 = phi( main/main::c#0, main::@2/main::c#1 )
+  main::b#3 = phi( main/main::b#0, main::@2/main::b#1 )
+  main::a#3 = phi( main/main::a#0, main::@2/main::a#1 )
+  main::i#2 = phi( main/main::i#0, main::@2/main::i#1 )
+  main::$0 = main::i#2 < $a
+  if(main::$0) goto main::@2
+  to:main::@return
+main::@2: scope:[main]  from main::@1
+  main::h#2 = phi( main::@1/main::h#3 )
+  main::g#2 = phi( main::@1/main::g#3 )
+  main::f#2 = phi( main::@1/main::f#3 )
+  main::e#2 = phi( main::@1/main::e#3 )
+  main::d#2 = phi( main::@1/main::d#3 )
+  main::c#2 = phi( main::@1/main::c#3 )
+  main::b#2 = phi( main::@1/main::b#3 )
+  main::a#2 = phi( main::@1/main::a#3 )
+  main::i#3 = phi( main::@1/main::i#2 )
+  main::$1 = main::i#3 * SIZEOF_INT
+  main::SCREEN[main::$1] = main::a#2
+  main::a#1 = ++ main::a#2
+  main::$2 = main::i#3 * SIZEOF_INT
+  main::SCREEN[main::$2] = main::b#2
+  main::b#1 = ++ main::b#2
+  main::$3 = main::i#3 * SIZEOF_INT
+  main::SCREEN[main::$3] = main::c#2
+  main::c#1 = ++ main::c#2
+  main::$4 = main::i#3 * SIZEOF_INT
+  main::SCREEN[main::$4] = main::d#2
+  main::d#1 = ++ main::d#2
+  main::$5 = main::i#3 * SIZEOF_INT
+  main::SCREEN[main::$5] = main::e#2
+  main::e#1 = ++ main::e#2
+  main::$6 = main::i#3 * SIZEOF_INT
+  main::SCREEN[main::$6] = main::f#2
+  main::f#1 = ++ main::f#2
+  main::$7 = main::i#3 * SIZEOF_INT
+  main::SCREEN[main::$7] = main::g#2
+  main::g#1 = ++ main::g#2
+  main::$8 = main::i#3 * SIZEOF_INT
+  main::SCREEN[main::$8] = main::h#2
+  main::h#1 = ++ main::h#2
+  main::i#1 = ++ main::i#3
+  to:main::@1
+main::@return: scope:[main]  from main::@1
+  return 
+  to:@return
+
+void __start()
+__start: scope:[__start]  from
+  call main
+  to:__start::@1
+__start::@1: scope:[__start]  from __start
+  to:__start::@return
+__start::@return: scope:[__start]  from __start::@1
+  return 
+  to:@return
+
+SYMBOL TABLE SSA
+__constant char SIZEOF_INT = 2
+void __start()
+void main()
+bool main::$0
+char main::$1
+char main::$2
+char main::$3
+char main::$4
+char main::$5
+char main::$6
+char main::$7
+char main::$8
+__constant int * const main::SCREEN = (int *)$400
+int main::a
+int main::a#0
+int main::a#1
+int main::a#2
+int main::a#3
+int main::b
+int main::b#0
+int main::b#1
+int main::b#2
+int main::b#3
+int main::c
+int main::c#0
+int main::c#1
+int main::c#2
+int main::c#3
+int main::d
+int main::d#0
+int main::d#1
+int main::d#2
+int main::d#3
+int main::e
+int main::e#0
+int main::e#1
+int main::e#2
+int main::e#3
+int main::f
+int main::f#0
+int main::f#1
+int main::f#2
+int main::f#3
+int main::g
+int main::g#0
+int main::g#1
+int main::g#2
+int main::g#3
+int main::h
+int main::h#0
+int main::h#1
+int main::h#2
+int main::h#3
+char main::i
+char main::i#0
+char main::i#1
+char main::i#2
+char main::i#3
+
+Adding number conversion cast (unumber) $a in main::$0 = main::i#2 < $a
+Successful SSA optimization PassNAddNumberTypeConversions
+Simplifying constant pointer cast (int *) 1024
+Simplifying constant integer cast $a
+Successful SSA optimization PassNCastSimplification
+Finalized unsigned number type (char) $a
+Successful SSA optimization PassNFinalizeNumberTypeConversions
+Alias main::i#2 = main::i#3 
+Alias main::a#2 = main::a#3 
+Alias main::b#2 = main::b#3 
+Alias main::c#2 = main::c#3 
+Alias main::d#2 = main::d#3 
+Alias main::e#2 = main::e#3 
+Alias main::f#2 = main::f#3 
+Alias main::g#2 = main::g#3 
+Alias main::h#2 = main::h#3 
+Successful SSA optimization Pass2AliasElimination
+Identified duplicate assignment right side [16] main::$2 = main::i#2 * SIZEOF_INT
+Identified duplicate assignment right side [19] main::$3 = main::i#2 * SIZEOF_INT
+Identified duplicate assignment right side [22] main::$4 = main::i#2 * SIZEOF_INT
+Identified duplicate assignment right side [25] main::$5 = main::i#2 * SIZEOF_INT
+Identified duplicate assignment right side [28] main::$6 = main::i#2 * SIZEOF_INT
+Identified duplicate assignment right side [31] main::$7 = main::i#2 * SIZEOF_INT
+Identified duplicate assignment right side [34] main::$8 = main::i#2 * SIZEOF_INT
+Successful SSA optimization Pass2DuplicateRValueIdentification
+Simple Condition main::$0 [11] if(main::i#2<$a) goto main::@2
+Successful SSA optimization Pass2ConditionalJumpSimplification
+Constant main::a#0 = 0
+Constant main::b#0 = 0
+Constant main::c#0 = 0
+Constant main::d#0 = 0
+Constant main::e#0 = 0
+Constant main::f#0 = 0
+Constant main::g#0 = 0
+Constant main::h#0 = 0
+Constant main::i#0 = 0
+Successful SSA optimization Pass2ConstantIdentification
+Removing unused procedure __start
+Removing unused procedure block __start
+Removing unused procedure block __start::@1
+Removing unused procedure block __start::@return
+Successful SSA optimization PassNEliminateEmptyStart
+Alias main::$2 = main::$1 main::$3 main::$4 main::$5 main::$6 main::$7 main::$8 
+Successful SSA optimization Pass2AliasElimination
+Rewriting multiplication to use shift [2] main::$2 = main::i#2 * SIZEOF_INT
+Successful SSA optimization Pass2MultiplyToShiftRewriting
+Inlining constant with var siblings main::a#0
+Inlining constant with var siblings main::b#0
+Inlining constant with var siblings main::c#0
+Inlining constant with var siblings main::d#0
+Inlining constant with var siblings main::e#0
+Inlining constant with var siblings main::f#0
+Inlining constant with var siblings main::g#0
+Inlining constant with var siblings main::h#0
+Inlining constant with var siblings main::i#0
+Constant inlined main::a#0 = 0
+Constant inlined main::c#0 = 0
+Constant inlined main::b#0 = 0
+Constant inlined main::i#0 = 0
+Constant inlined main::h#0 = 0
+Constant inlined main::e#0 = 0
+Constant inlined main::d#0 = 0
+Constant inlined main::g#0 = 0
+Constant inlined main::f#0 = 0
+Successful SSA optimization Pass2ConstantInlining
+Eliminating unused constant SIZEOF_INT
+Successful SSA optimization PassNEliminateUnusedVars
+Adding NOP phi() at start of main
+CALL GRAPH
+
+Created 9 initial phi equivalence classes
+Coalesced [22] main::i#4 = main::i#1
+Coalesced [23] main::a#4 = main::a#1
+Coalesced [24] main::b#4 = main::b#1
+Coalesced [25] main::c#4 = main::c#1
+Coalesced [26] main::d#4 = main::d#1
+Coalesced [27] main::e#4 = main::e#1
+Coalesced [28] main::f#4 = main::f#1
+Coalesced [29] main::g#4 = main::g#1
+Coalesced [30] main::h#4 = main::h#1
+Coalesced down to 9 phi equivalence classes
+Adding NOP phi() at start of main
+
+FINAL CONTROL FLOW GRAPH
+
+void main()
+main: scope:[main]  from
+  [0] phi()
+  to:main::@1
+main::@1: scope:[main]  from main main::@2
+  [1] main::h#2 = phi( main/0, main::@2/main::h#1 )
+  [1] main::g#2 = phi( main/0, main::@2/main::g#1 )
+  [1] main::f#2 = phi( main/0, main::@2/main::f#1 )
+  [1] main::e#2 = phi( main/0, main::@2/main::e#1 )
+  [1] main::d#2 = phi( main/0, main::@2/main::d#1 )
+  [1] main::c#2 = phi( main/0, main::@2/main::c#1 )
+  [1] main::b#2 = phi( main/0, main::@2/main::b#1 )
+  [1] main::a#2 = phi( main/0, main::@2/main::a#1 )
+  [1] main::i#2 = phi( main/0, main::@2/main::i#1 )
+  [2] if(main::i#2<$a) goto main::@2
+  to:main::@return
+main::@return: scope:[main]  from main::@1
+  [3] return 
+  to:@return
+main::@2: scope:[main]  from main::@1
+  [4] main::$2 = main::i#2 << 1
+  [5] main::SCREEN[main::$2] = main::a#2
+  [6] main::a#1 = ++ main::a#2
+  [7] main::SCREEN[main::$2] = main::b#2
+  [8] main::b#1 = ++ main::b#2
+  [9] main::SCREEN[main::$2] = main::c#2
+  [10] main::c#1 = ++ main::c#2
+  [11] main::SCREEN[main::$2] = main::d#2
+  [12] main::d#1 = ++ main::d#2
+  [13] main::SCREEN[main::$2] = main::e#2
+  [14] main::e#1 = ++ main::e#2
+  [15] main::SCREEN[main::$2] = main::f#2
+  [16] main::f#1 = ++ main::f#2
+  [17] main::SCREEN[main::$2] = main::g#2
+  [18] main::g#1 = ++ main::g#2
+  [19] main::SCREEN[main::$2] = main::h#2
+  [20] main::h#1 = ++ main::h#2
+  [21] main::i#1 = ++ main::i#2
+  to:main::@1
+
+
+VARIABLE REGISTER WEIGHTS
+void main()
+char main::$2 // 6.6
+int main::a
+int main::a#1 // 1.375
+int main::a#2 // 8.25
+int main::b
+int main::b#1 // 1.5714285714285714
+int main::b#2 // 5.5
+int main::c
+int main::c#1 // 1.8333333333333333
+int main::c#2 // 4.125
+int main::d
+int main::d#1 // 2.2
+int main::d#2 // 3.3000000000000003
+int main::e
+int main::e#1 // 2.75
+int main::e#2 // 2.75
+int main::f
+int main::f#1 // 3.6666666666666665
+int main::f#2 // 2.357142857142857
+int main::g
+int main::g#1 // 5.5
+int main::g#2 // 2.0625
+int main::h
+int main::h#1 // 11.0
+int main::h#2 // 1.8333333333333335
+char main::i
+char main::i#1 // 22.0
+char main::i#2 // 2.3157894736842106
+
+Initial phi equivalence classes
+[ main::i#2 main::i#1 ]
+[ main::a#2 main::a#1 ]
+[ main::b#2 main::b#1 ]
+[ main::c#2 main::c#1 ]
+[ main::d#2 main::d#1 ]
+[ main::e#2 main::e#1 ]
+[ main::f#2 main::f#1 ]
+[ main::g#2 main::g#1 ]
+[ main::h#2 main::h#1 ]
+Added variable main::$2 to live range equivalence class [ main::$2 ]
+Complete equivalence classes
+[ main::i#2 main::i#1 ]
+[ main::a#2 main::a#1 ]
+[ main::b#2 main::b#1 ]
+[ main::c#2 main::c#1 ]
+[ main::d#2 main::d#1 ]
+[ main::e#2 main::e#1 ]
+[ main::f#2 main::f#1 ]
+[ main::g#2 main::g#1 ]
+[ main::h#2 main::h#1 ]
+[ main::$2 ]
+Allocated zp[1]:251 [ main::i#2 main::i#1 ]
+Allocated zp[2]:252 [ main::a#2 main::a#1 ]
+Allocated zp[2]:254 [ main::b#2 main::b#1 ]
+Zero-page exhausted. Moving allocation to main memory main::c#2
+Allocated mem[2] [ main::c#2 main::c#1 ]
+Zero-page exhausted. Moving allocation to main memory main::d#2
+Allocated mem[2] [ main::d#2 main::d#1 ]
+Zero-page exhausted. Moving allocation to main memory main::e#2
+Allocated mem[2] [ main::e#2 main::e#1 ]
+Zero-page exhausted. Moving allocation to main memory main::f#2
+Allocated mem[2] [ main::f#2 main::f#1 ]
+Zero-page exhausted. Moving allocation to main memory main::g#2
+Allocated mem[2] [ main::g#2 main::g#1 ]
+Zero-page exhausted. Moving allocation to main memory main::h#2
+Allocated mem[2] [ main::h#2 main::h#1 ]
+Zero-page exhausted. Moving allocation to main memory main::$2
+Allocated mem[1] [ main::$2 ]
+REGISTER UPLIFT POTENTIAL REGISTERS
+Statement [4] main::$2 = main::i#2 << 1 [ main::i#2 main::a#2 main::b#2 main::c#2 main::d#2 main::e#2 main::f#2 main::g#2 main::h#2 main::$2 ] (  [ main::i#2 main::a#2 main::b#2 main::c#2 main::d#2 main::e#2 main::f#2 main::g#2 main::h#2 main::$2 ] { }  ) always clobbers reg byte a 
+Removing always clobbered register reg byte a as potential for zp[1]:251 [ main::i#2 main::i#1 ]
+Statement [5] main::SCREEN[main::$2] = main::a#2 [ main::i#2 main::a#2 main::b#2 main::c#2 main::d#2 main::e#2 main::f#2 main::g#2 main::h#2 main::$2 ] (  [ main::i#2 main::a#2 main::b#2 main::c#2 main::d#2 main::e#2 main::f#2 main::g#2 main::h#2 main::$2 ] { }  ) always clobbers reg byte a 
+Removing always clobbered register reg byte a as potential for mem[1] [ main::$2 ]
+Statement [7] main::SCREEN[main::$2] = main::b#2 [ main::i#2 main::b#2 main::c#2 main::d#2 main::e#2 main::f#2 main::g#2 main::h#2 main::a#1 main::$2 ] (  [ main::i#2 main::b#2 main::c#2 main::d#2 main::e#2 main::f#2 main::g#2 main::h#2 main::a#1 main::$2 ] { }  ) always clobbers reg byte a 
+Statement [9] main::SCREEN[main::$2] = main::c#2 [ main::i#2 main::c#2 main::d#2 main::e#2 main::f#2 main::g#2 main::h#2 main::a#1 main::b#1 main::$2 ] (  [ main::i#2 main::c#2 main::d#2 main::e#2 main::f#2 main::g#2 main::h#2 main::a#1 main::b#1 main::$2 ] { }  ) always clobbers reg byte a 
+Statement [11] main::SCREEN[main::$2] = main::d#2 [ main::i#2 main::d#2 main::e#2 main::f#2 main::g#2 main::h#2 main::a#1 main::b#1 main::c#1 main::$2 ] (  [ main::i#2 main::d#2 main::e#2 main::f#2 main::g#2 main::h#2 main::a#1 main::b#1 main::c#1 main::$2 ] { }  ) always clobbers reg byte a 
+Statement [13] main::SCREEN[main::$2] = main::e#2 [ main::i#2 main::e#2 main::f#2 main::g#2 main::h#2 main::a#1 main::b#1 main::c#1 main::d#1 main::$2 ] (  [ main::i#2 main::e#2 main::f#2 main::g#2 main::h#2 main::a#1 main::b#1 main::c#1 main::d#1 main::$2 ] { }  ) always clobbers reg byte a 
+Statement [15] main::SCREEN[main::$2] = main::f#2 [ main::i#2 main::f#2 main::g#2 main::h#2 main::a#1 main::b#1 main::c#1 main::d#1 main::e#1 main::$2 ] (  [ main::i#2 main::f#2 main::g#2 main::h#2 main::a#1 main::b#1 main::c#1 main::d#1 main::e#1 main::$2 ] { }  ) always clobbers reg byte a 
+Statement [17] main::SCREEN[main::$2] = main::g#2 [ main::i#2 main::g#2 main::h#2 main::a#1 main::b#1 main::c#1 main::d#1 main::e#1 main::f#1 main::$2 ] (  [ main::i#2 main::g#2 main::h#2 main::a#1 main::b#1 main::c#1 main::d#1 main::e#1 main::f#1 main::$2 ] { }  ) always clobbers reg byte a 
+Statement [19] main::SCREEN[main::$2] = main::h#2 [ main::i#2 main::h#2 main::a#1 main::b#1 main::c#1 main::d#1 main::e#1 main::f#1 main::g#1 ] (  [ main::i#2 main::h#2 main::a#1 main::b#1 main::c#1 main::d#1 main::e#1 main::f#1 main::g#1 ] { }  ) always clobbers reg byte a 
+Statement [4] main::$2 = main::i#2 << 1 [ main::i#2 main::a#2 main::b#2 main::c#2 main::d#2 main::e#2 main::f#2 main::g#2 main::h#2 main::$2 ] (  [ main::i#2 main::a#2 main::b#2 main::c#2 main::d#2 main::e#2 main::f#2 main::g#2 main::h#2 main::$2 ] { }  ) always clobbers reg byte a 
+Statement [5] main::SCREEN[main::$2] = main::a#2 [ main::i#2 main::a#2 main::b#2 main::c#2 main::d#2 main::e#2 main::f#2 main::g#2 main::h#2 main::$2 ] (  [ main::i#2 main::a#2 main::b#2 main::c#2 main::d#2 main::e#2 main::f#2 main::g#2 main::h#2 main::$2 ] { }  ) always clobbers reg byte a 
+Statement [7] main::SCREEN[main::$2] = main::b#2 [ main::i#2 main::b#2 main::c#2 main::d#2 main::e#2 main::f#2 main::g#2 main::h#2 main::a#1 main::$2 ] (  [ main::i#2 main::b#2 main::c#2 main::d#2 main::e#2 main::f#2 main::g#2 main::h#2 main::a#1 main::$2 ] { }  ) always clobbers reg byte a 
+Statement [9] main::SCREEN[main::$2] = main::c#2 [ main::i#2 main::c#2 main::d#2 main::e#2 main::f#2 main::g#2 main::h#2 main::a#1 main::b#1 main::$2 ] (  [ main::i#2 main::c#2 main::d#2 main::e#2 main::f#2 main::g#2 main::h#2 main::a#1 main::b#1 main::$2 ] { }  ) always clobbers reg byte a 
+Statement [11] main::SCREEN[main::$2] = main::d#2 [ main::i#2 main::d#2 main::e#2 main::f#2 main::g#2 main::h#2 main::a#1 main::b#1 main::c#1 main::$2 ] (  [ main::i#2 main::d#2 main::e#2 main::f#2 main::g#2 main::h#2 main::a#1 main::b#1 main::c#1 main::$2 ] { }  ) always clobbers reg byte a 
+Statement [13] main::SCREEN[main::$2] = main::e#2 [ main::i#2 main::e#2 main::f#2 main::g#2 main::h#2 main::a#1 main::b#1 main::c#1 main::d#1 main::$2 ] (  [ main::i#2 main::e#2 main::f#2 main::g#2 main::h#2 main::a#1 main::b#1 main::c#1 main::d#1 main::$2 ] { }  ) always clobbers reg byte a 
+Statement [15] main::SCREEN[main::$2] = main::f#2 [ main::i#2 main::f#2 main::g#2 main::h#2 main::a#1 main::b#1 main::c#1 main::d#1 main::e#1 main::$2 ] (  [ main::i#2 main::f#2 main::g#2 main::h#2 main::a#1 main::b#1 main::c#1 main::d#1 main::e#1 main::$2 ] { }  ) always clobbers reg byte a 
+Statement [17] main::SCREEN[main::$2] = main::g#2 [ main::i#2 main::g#2 main::h#2 main::a#1 main::b#1 main::c#1 main::d#1 main::e#1 main::f#1 main::$2 ] (  [ main::i#2 main::g#2 main::h#2 main::a#1 main::b#1 main::c#1 main::d#1 main::e#1 main::f#1 main::$2 ] { }  ) always clobbers reg byte a 
+Statement [19] main::SCREEN[main::$2] = main::h#2 [ main::i#2 main::h#2 main::a#1 main::b#1 main::c#1 main::d#1 main::e#1 main::f#1 main::g#1 ] (  [ main::i#2 main::h#2 main::a#1 main::b#1 main::c#1 main::d#1 main::e#1 main::f#1 main::g#1 ] { }  ) always clobbers reg byte a 
+Potential registers zp[1]:251 [ main::i#2 main::i#1 ] : zp[1]:251 , reg byte x , reg byte y , 
+Potential registers zp[2]:252 [ main::a#2 main::a#1 ] : zp[2]:252 , 
+Potential registers zp[2]:254 [ main::b#2 main::b#1 ] : zp[2]:254 , 
+Potential registers mem[2] [ main::c#2 main::c#1 ] : mem[2] , 
+Potential registers mem[2] [ main::d#2 main::d#1 ] : mem[2] , 
+Potential registers mem[2] [ main::e#2 main::e#1 ] : mem[2] , 
+Potential registers mem[2] [ main::f#2 main::f#1 ] : mem[2] , 
+Potential registers mem[2] [ main::g#2 main::g#1 ] : mem[2] , 
+Potential registers mem[2] [ main::h#2 main::h#1 ] : mem[2] , 
+Potential registers mem[1] [ main::$2 ] : mem[1] , reg byte x , reg byte y , 
+
+REGISTER UPLIFT SCOPES
+Uplift Scope [main] 24.32: zp[1]:251 [ main::i#2 main::i#1 ] 12.83: mem[2] [ main::h#2 main::h#1 ] 9.62: zp[2]:252 [ main::a#2 main::a#1 ] 7.56: mem[2] [ main::g#2 main::g#1 ] 7.07: zp[2]:254 [ main::b#2 main::b#1 ] 6.6: mem[1] [ main::$2 ] 6.02: mem[2] [ main::f#2 main::f#1 ] 5.96: mem[2] [ main::c#2 main::c#1 ] 5.5: mem[2] [ main::d#2 main::d#1 ] 5.5: mem[2] [ main::e#2 main::e#1 ] 
+Uplift Scope [] 
+
+Uplifting [main] best 3681 combination reg byte y [ main::i#2 main::i#1 ] mem[2] [ main::h#2 main::h#1 ] zp[2]:252 [ main::a#2 main::a#1 ] mem[2] [ main::g#2 main::g#1 ] zp[2]:254 [ main::b#2 main::b#1 ] reg byte x [ main::$2 ] mem[2] [ main::f#2 main::f#1 ] mem[2] [ main::c#2 main::c#1 ] mem[2] [ main::d#2 main::d#1 ] mem[2] [ main::e#2 main::e#1 ] 
+Uplifting [] best 3681 combination 
+Allocated (was zp[2]:252) zp[2]:251 [ main::a#2 main::a#1 ]
+Allocated (was zp[2]:254) zp[2]:253 [ main::b#2 main::b#1 ]
+
+ASSEMBLER BEFORE OPTIMIZATION
+  // File Comments
+// Tests that variables overflow to main memory when zeropage is exhausted
+  // Upstart
+  // Commodore 64 PRG executable file
+.file [name="zeropage-overflow.prg", type="prg", segments="Program"]
+.segmentdef Program [segments="Basic, Code, Data"]
+.segmentdef Basic [start=$0801]
+.segmentdef Code [start=$80d]
+.segmentdef Data [startAfter="Code"]
+.segment Basic
+:BasicUpstart(main)
+  // Global Constants & labels
+.segment Code
+  // main
+// And then allocate a bunch of variables
+main: {
+    .label SCREEN = $400
+    .label a = $fb
+    .label b = $fd
+    // [1] phi from main to main::@1 [phi:main->main::@1]
+  __b1_from_main:
+    // [1] phi main::h#2 = 0 [phi:main->main::@1#0] -- vwsm1=vwsc1 
+    lda #<0
+    sta h
+    lda #>0
+    sta h+1
+    // [1] phi main::g#2 = 0 [phi:main->main::@1#1] -- vwsm1=vwsc1 
+    lda #<0
+    sta g
+    lda #>0
+    sta g+1
+    // [1] phi main::f#2 = 0 [phi:main->main::@1#2] -- vwsm1=vwsc1 
+    lda #<0
+    sta f
+    lda #>0
+    sta f+1
+    // [1] phi main::e#2 = 0 [phi:main->main::@1#3] -- vwsm1=vwsc1 
+    lda #<0
+    sta e
+    lda #>0
+    sta e+1
+    // [1] phi main::d#2 = 0 [phi:main->main::@1#4] -- vwsm1=vwsc1 
+    lda #<0
+    sta d
+    lda #>0
+    sta d+1
+    // [1] phi main::c#2 = 0 [phi:main->main::@1#5] -- vwsm1=vwsc1 
+    lda #<0
+    sta c
+    lda #>0
+    sta c+1
+    // [1] phi main::b#2 = 0 [phi:main->main::@1#6] -- vwsz1=vwsc1 
+    lda #<0
+    sta.z b
+    lda #>0
+    sta.z b+1
+    // [1] phi main::a#2 = 0 [phi:main->main::@1#7] -- vwsz1=vwsc1 
+    lda #<0
+    sta.z a
+    lda #>0
+    sta.z a+1
+    // [1] phi main::i#2 = 0 [phi:main->main::@1#8] -- vbuyy=vbuc1 
+    ldy #0
+    jmp __b1
+    // main::@1
+  __b1:
+    // [2] if(main::i#2<$a) goto main::@2 -- vbuyy_lt_vbuc1_then_la1 
+    cpy #$a
+    bcc __b2
+    jmp __breturn
+    // main::@return
+  __breturn:
+    // [3] return 
+    rts
+    // main::@2
+  __b2:
+    // [4] main::$2 = main::i#2 << 1 -- vbuxx=vbuyy_rol_1 
+    tya
+    asl
+    tax
+    // [5] main::SCREEN[main::$2] = main::a#2 -- pwsc1_derefidx_vbuxx=vwsz1 
+    lda.z a
+    sta SCREEN,x
+    lda.z a+1
+    sta SCREEN+1,x
+    // [6] main::a#1 = ++ main::a#2 -- vwsz1=_inc_vwsz1 
+    inc.z a
+    bne !+
+    inc.z a+1
+  !:
+    // [7] main::SCREEN[main::$2] = main::b#2 -- pwsc1_derefidx_vbuxx=vwsz1 
+    lda.z b
+    sta SCREEN,x
+    lda.z b+1
+    sta SCREEN+1,x
+    // [8] main::b#1 = ++ main::b#2 -- vwsz1=_inc_vwsz1 
+    inc.z b
+    bne !+
+    inc.z b+1
+  !:
+    // [9] main::SCREEN[main::$2] = main::c#2 -- pwsc1_derefidx_vbuxx=vwsm1 
+    lda c
+    sta SCREEN,x
+    lda c+1
+    sta SCREEN+1,x
+    // [10] main::c#1 = ++ main::c#2 -- vwsm1=_inc_vwsm1 
+    inc c
+    bne !+
+    inc c+1
+  !:
+    // [11] main::SCREEN[main::$2] = main::d#2 -- pwsc1_derefidx_vbuxx=vwsm1 
+    lda d
+    sta SCREEN,x
+    lda d+1
+    sta SCREEN+1,x
+    // [12] main::d#1 = ++ main::d#2 -- vwsm1=_inc_vwsm1 
+    inc d
+    bne !+
+    inc d+1
+  !:
+    // [13] main::SCREEN[main::$2] = main::e#2 -- pwsc1_derefidx_vbuxx=vwsm1 
+    lda e
+    sta SCREEN,x
+    lda e+1
+    sta SCREEN+1,x
+    // [14] main::e#1 = ++ main::e#2 -- vwsm1=_inc_vwsm1 
+    inc e
+    bne !+
+    inc e+1
+  !:
+    // [15] main::SCREEN[main::$2] = main::f#2 -- pwsc1_derefidx_vbuxx=vwsm1 
+    lda f
+    sta SCREEN,x
+    lda f+1
+    sta SCREEN+1,x
+    // [16] main::f#1 = ++ main::f#2 -- vwsm1=_inc_vwsm1 
+    inc f
+    bne !+
+    inc f+1
+  !:
+    // [17] main::SCREEN[main::$2] = main::g#2 -- pwsc1_derefidx_vbuxx=vwsm1 
+    lda g
+    sta SCREEN,x
+    lda g+1
+    sta SCREEN+1,x
+    // [18] main::g#1 = ++ main::g#2 -- vwsm1=_inc_vwsm1 
+    inc g
+    bne !+
+    inc g+1
+  !:
+    // [19] main::SCREEN[main::$2] = main::h#2 -- pwsc1_derefidx_vbuxx=vwsm1 
+    lda h
+    sta SCREEN,x
+    lda h+1
+    sta SCREEN+1,x
+    // [20] main::h#1 = ++ main::h#2 -- vwsm1=_inc_vwsm1 
+    inc h
+    bne !+
+    inc h+1
+  !:
+    // [21] main::i#1 = ++ main::i#2 -- vbuyy=_inc_vbuyy 
+    iny
+    // [1] phi from main::@2 to main::@1 [phi:main::@2->main::@1]
+  __b1_from___b2:
+    // [1] phi main::h#2 = main::h#1 [phi:main::@2->main::@1#0] -- register_copy 
+    // [1] phi main::g#2 = main::g#1 [phi:main::@2->main::@1#1] -- register_copy 
+    // [1] phi main::f#2 = main::f#1 [phi:main::@2->main::@1#2] -- register_copy 
+    // [1] phi main::e#2 = main::e#1 [phi:main::@2->main::@1#3] -- register_copy 
+    // [1] phi main::d#2 = main::d#1 [phi:main::@2->main::@1#4] -- register_copy 
+    // [1] phi main::c#2 = main::c#1 [phi:main::@2->main::@1#5] -- register_copy 
+    // [1] phi main::b#2 = main::b#1 [phi:main::@2->main::@1#6] -- register_copy 
+    // [1] phi main::a#2 = main::a#1 [phi:main::@2->main::@1#7] -- register_copy 
+    // [1] phi main::i#2 = main::i#1 [phi:main::@2->main::@1#8] -- register_copy 
+    jmp __b1
+  .segment Data
+    c: .word 0
+    d: .word 0
+    e: .word 0
+    f: .word 0
+    g: .word 0
+    h: .word 0
+}
+  // File Data
+
+ASSEMBLER OPTIMIZATIONS
+Removing instruction jmp __b1
+Removing instruction jmp __breturn
+Succesful ASM optimization Pass5NextJumpElimination
+Removing instruction lda #>0
+Removing instruction lda #<0
+Removing instruction lda #>0
+Removing instruction lda #<0
+Removing instruction lda #>0
+Removing instruction lda #<0
+Removing instruction lda #>0
+Removing instruction lda #<0
+Removing instruction lda #>0
+Removing instruction lda #<0
+Removing instruction lda #>0
+Removing instruction lda #<0
+Removing instruction lda #>0
+Removing instruction lda #<0
+Removing instruction lda #>0
+Replacing instruction ldy #0 with TAY
+Succesful ASM optimization Pass5UnnecesaryLoadElimination
+Removing instruction __b1_from_main:
+Removing instruction __breturn:
+Removing instruction __b1_from___b2:
+Succesful ASM optimization Pass5UnusedLabelElimination
+
+FINAL SYMBOL TABLE
+void main()
+char main::$2 // reg byte x 6.6
+__constant int * const main::SCREEN = (int *) 1024
+int main::a
+int main::a#1 // a zp[2]:251 1.375
+int main::a#2 // a zp[2]:251 8.25
+int main::b
+int main::b#1 // b zp[2]:253 1.5714285714285714
+int main::b#2 // b zp[2]:253 5.5
+int main::c
+int main::c#1 // c mem[2] 1.8333333333333333
+int main::c#2 // c mem[2] 4.125
+int main::d
+int main::d#1 // d mem[2] 2.2
+int main::d#2 // d mem[2] 3.3000000000000003
+int main::e
+int main::e#1 // e mem[2] 2.75
+int main::e#2 // e mem[2] 2.75
+int main::f
+int main::f#1 // f mem[2] 3.6666666666666665
+int main::f#2 // f mem[2] 2.357142857142857
+int main::g
+int main::g#1 // g mem[2] 5.5
+int main::g#2 // g mem[2] 2.0625
+int main::h
+int main::h#1 // h mem[2] 11.0
+int main::h#2 // h mem[2] 1.8333333333333335
+char main::i
+char main::i#1 // reg byte y 22.0
+char main::i#2 // reg byte y 2.3157894736842106
+
+reg byte y [ main::i#2 main::i#1 ]
+zp[2]:251 [ main::a#2 main::a#1 ]
+zp[2]:253 [ main::b#2 main::b#1 ]
+mem[2] [ main::c#2 main::c#1 ]
+mem[2] [ main::d#2 main::d#1 ]
+mem[2] [ main::e#2 main::e#1 ]
+mem[2] [ main::f#2 main::f#1 ]
+mem[2] [ main::g#2 main::g#1 ]
+mem[2] [ main::h#2 main::h#1 ]
+reg byte x [ main::$2 ]
+
+
+FINAL ASSEMBLER
+Score: 3321
+
+  // File Comments
+// Tests that variables overflow to main memory when zeropage is exhausted
+  // Upstart
+  // Commodore 64 PRG executable file
+.file [name="zeropage-overflow.prg", type="prg", segments="Program"]
+.segmentdef Program [segments="Basic, Code, Data"]
+.segmentdef Basic [start=$0801]
+.segmentdef Code [start=$80d]
+.segmentdef Data [startAfter="Code"]
+.segment Basic
+:BasicUpstart(main)
+  // Global Constants & labels
+.segment Code
+  // main
+// And then allocate a bunch of variables
+main: {
+    .label SCREEN = $400
+    .label a = $fb
+    .label b = $fd
+    // [1] phi from main to main::@1 [phi:main->main::@1]
+    // [1] phi main::h#2 = 0 [phi:main->main::@1#0] -- vwsm1=vwsc1 
+    lda #<0
+    sta h
+    sta h+1
+    // [1] phi main::g#2 = 0 [phi:main->main::@1#1] -- vwsm1=vwsc1 
+    sta g
+    sta g+1
+    // [1] phi main::f#2 = 0 [phi:main->main::@1#2] -- vwsm1=vwsc1 
+    sta f
+    sta f+1
+    // [1] phi main::e#2 = 0 [phi:main->main::@1#3] -- vwsm1=vwsc1 
+    sta e
+    sta e+1
+    // [1] phi main::d#2 = 0 [phi:main->main::@1#4] -- vwsm1=vwsc1 
+    sta d
+    sta d+1
+    // [1] phi main::c#2 = 0 [phi:main->main::@1#5] -- vwsm1=vwsc1 
+    sta c
+    sta c+1
+    // [1] phi main::b#2 = 0 [phi:main->main::@1#6] -- vwsz1=vwsc1 
+    sta.z b
+    sta.z b+1
+    // [1] phi main::a#2 = 0 [phi:main->main::@1#7] -- vwsz1=vwsc1 
+    sta.z a
+    sta.z a+1
+    // [1] phi main::i#2 = 0 [phi:main->main::@1#8] -- vbuyy=vbuc1 
+    tay
+    // main::@1
+  __b1:
+    // for(char i=0;i<10;i++)
+    // [2] if(main::i#2<$a) goto main::@2 -- vbuyy_lt_vbuc1_then_la1 
+    cpy #$a
+    bcc __b2
+    // main::@return
+    // }
+    // [3] return 
+    rts
+    // main::@2
+  __b2:
+    // SCREEN[i] = a++
+    // [4] main::$2 = main::i#2 << 1 -- vbuxx=vbuyy_rol_1 
+    tya
+    asl
+    tax
+    // [5] main::SCREEN[main::$2] = main::a#2 -- pwsc1_derefidx_vbuxx=vwsz1 
+    lda.z a
+    sta SCREEN,x
+    lda.z a+1
+    sta SCREEN+1,x
+    // SCREEN[i] = a++;
+    // [6] main::a#1 = ++ main::a#2 -- vwsz1=_inc_vwsz1 
+    inc.z a
+    bne !+
+    inc.z a+1
+  !:
+    // SCREEN[i] = b++
+    // [7] main::SCREEN[main::$2] = main::b#2 -- pwsc1_derefidx_vbuxx=vwsz1 
+    lda.z b
+    sta SCREEN,x
+    lda.z b+1
+    sta SCREEN+1,x
+    // SCREEN[i] = b++;
+    // [8] main::b#1 = ++ main::b#2 -- vwsz1=_inc_vwsz1 
+    inc.z b
+    bne !+
+    inc.z b+1
+  !:
+    // SCREEN[i] = c++
+    // [9] main::SCREEN[main::$2] = main::c#2 -- pwsc1_derefidx_vbuxx=vwsm1 
+    lda c
+    sta SCREEN,x
+    lda c+1
+    sta SCREEN+1,x
+    // SCREEN[i] = c++;
+    // [10] main::c#1 = ++ main::c#2 -- vwsm1=_inc_vwsm1 
+    inc c
+    bne !+
+    inc c+1
+  !:
+    // SCREEN[i] = d++
+    // [11] main::SCREEN[main::$2] = main::d#2 -- pwsc1_derefidx_vbuxx=vwsm1 
+    lda d
+    sta SCREEN,x
+    lda d+1
+    sta SCREEN+1,x
+    // SCREEN[i] = d++;
+    // [12] main::d#1 = ++ main::d#2 -- vwsm1=_inc_vwsm1 
+    inc d
+    bne !+
+    inc d+1
+  !:
+    // SCREEN[i] = e++
+    // [13] main::SCREEN[main::$2] = main::e#2 -- pwsc1_derefidx_vbuxx=vwsm1 
+    lda e
+    sta SCREEN,x
+    lda e+1
+    sta SCREEN+1,x
+    // SCREEN[i] = e++;
+    // [14] main::e#1 = ++ main::e#2 -- vwsm1=_inc_vwsm1 
+    inc e
+    bne !+
+    inc e+1
+  !:
+    // SCREEN[i] = f++
+    // [15] main::SCREEN[main::$2] = main::f#2 -- pwsc1_derefidx_vbuxx=vwsm1 
+    lda f
+    sta SCREEN,x
+    lda f+1
+    sta SCREEN+1,x
+    // SCREEN[i] = f++;
+    // [16] main::f#1 = ++ main::f#2 -- vwsm1=_inc_vwsm1 
+    inc f
+    bne !+
+    inc f+1
+  !:
+    // SCREEN[i] = g++
+    // [17] main::SCREEN[main::$2] = main::g#2 -- pwsc1_derefidx_vbuxx=vwsm1 
+    lda g
+    sta SCREEN,x
+    lda g+1
+    sta SCREEN+1,x
+    // SCREEN[i] = g++;
+    // [18] main::g#1 = ++ main::g#2 -- vwsm1=_inc_vwsm1 
+    inc g
+    bne !+
+    inc g+1
+  !:
+    // SCREEN[i] = h++
+    // [19] main::SCREEN[main::$2] = main::h#2 -- pwsc1_derefidx_vbuxx=vwsm1 
+    lda h
+    sta SCREEN,x
+    lda h+1
+    sta SCREEN+1,x
+    // SCREEN[i] = h++;
+    // [20] main::h#1 = ++ main::h#2 -- vwsm1=_inc_vwsm1 
+    inc h
+    bne !+
+    inc h+1
+  !:
+    // for(char i=0;i<10;i++)
+    // [21] main::i#1 = ++ main::i#2 -- vbuyy=_inc_vbuyy 
+    iny
+    // [1] phi from main::@2 to main::@1 [phi:main::@2->main::@1]
+    // [1] phi main::h#2 = main::h#1 [phi:main::@2->main::@1#0] -- register_copy 
+    // [1] phi main::g#2 = main::g#1 [phi:main::@2->main::@1#1] -- register_copy 
+    // [1] phi main::f#2 = main::f#1 [phi:main::@2->main::@1#2] -- register_copy 
+    // [1] phi main::e#2 = main::e#1 [phi:main::@2->main::@1#3] -- register_copy 
+    // [1] phi main::d#2 = main::d#1 [phi:main::@2->main::@1#4] -- register_copy 
+    // [1] phi main::c#2 = main::c#1 [phi:main::@2->main::@1#5] -- register_copy 
+    // [1] phi main::b#2 = main::b#1 [phi:main::@2->main::@1#6] -- register_copy 
+    // [1] phi main::a#2 = main::a#1 [phi:main::@2->main::@1#7] -- register_copy 
+    // [1] phi main::i#2 = main::i#1 [phi:main::@2->main::@1#8] -- register_copy 
+    jmp __b1
+  .segment Data
+    c: .word 0
+    d: .word 0
+    e: .word 0
+    f: .word 0
+    g: .word 0
+    h: .word 0
+}
+  // File Data
+
diff --git a/src/test/ref/zeropage-overflow.sym b/src/test/ref/zeropage-overflow.sym
new file mode 100644
index 000000000..81e9d9a01
--- /dev/null
+++ b/src/test/ref/zeropage-overflow.sym
@@ -0,0 +1,41 @@
+void main()
+char main::$2 // reg byte x 6.6
+__constant int * const main::SCREEN = (int *) 1024
+int main::a
+int main::a#1 // a zp[2]:251 1.375
+int main::a#2 // a zp[2]:251 8.25
+int main::b
+int main::b#1 // b zp[2]:253 1.5714285714285714
+int main::b#2 // b zp[2]:253 5.5
+int main::c
+int main::c#1 // c mem[2] 1.8333333333333333
+int main::c#2 // c mem[2] 4.125
+int main::d
+int main::d#1 // d mem[2] 2.2
+int main::d#2 // d mem[2] 3.3000000000000003
+int main::e
+int main::e#1 // e mem[2] 2.75
+int main::e#2 // e mem[2] 2.75
+int main::f
+int main::f#1 // f mem[2] 3.6666666666666665
+int main::f#2 // f mem[2] 2.357142857142857
+int main::g
+int main::g#1 // g mem[2] 5.5
+int main::g#2 // g mem[2] 2.0625
+int main::h
+int main::h#1 // h mem[2] 11.0
+int main::h#2 // h mem[2] 1.8333333333333335
+char main::i
+char main::i#1 // reg byte y 22.0
+char main::i#2 // reg byte y 2.3157894736842106
+
+reg byte y [ main::i#2 main::i#1 ]
+zp[2]:251 [ main::a#2 main::a#1 ]
+zp[2]:253 [ main::b#2 main::b#1 ]
+mem[2] [ main::c#2 main::c#1 ]
+mem[2] [ main::d#2 main::d#1 ]
+mem[2] [ main::e#2 main::e#1 ]
+mem[2] [ main::f#2 main::f#1 ]
+mem[2] [ main::g#2 main::g#1 ]
+mem[2] [ main::h#2 main::h#1 ]
+reg byte x [ main::$2 ]