diff --git a/src/main/java/dk/camelot64/kickc/Compiler.java b/src/main/java/dk/camelot64/kickc/Compiler.java
index a84672de1..f7a603c82 100644
--- a/src/main/java/dk/camelot64/kickc/Compiler.java
+++ b/src/main/java/dk/camelot64/kickc/Compiler.java
@@ -29,6 +29,9 @@ public class Compiler {
    /** The number of combinations to test when uplifting variables into registers. */
    private int upliftCombinations = 100;
 
+   /** Tell the compiler to mimimize optimizations to increase performance. */
+   private boolean optimizeMinimal = false;
+
    public Compiler() {
       this.program = new Program();
    }
@@ -37,6 +40,10 @@ public class Compiler {
       this.upliftCombinations = upliftCombinations;
    }
 
+   public void setOptimizeMinimal(boolean optimizeMinimal) {
+      this.optimizeMinimal = optimizeMinimal;
+   }
+
    public void setLog(CompileLog compileLog) {
       program.setLog(compileLog);
    }
@@ -252,7 +259,7 @@ public class Compiler {
       optimizations.add(new Pass2DuplicateRValueIdentification(program));
       optimizations.add(new Pass2ConditionalJumpSimplification(program));
       optimizations.add(new Pass2ConditionalAndOrRewriting(program));
-      optimizations.add(new Pass2ConditionalJumpSequenceImprovement(program)); 
+      optimizations.add(new Pass2ConditionalJumpSequenceImprovement(program));
       optimizations.add(new Pass2ConstantRValueConsolidation(program));
       optimizations.add(new Pass2ConstantIdentification(program));
       optimizations.add(new Pass2ConstantValues(program));
@@ -464,21 +471,23 @@ public class Compiler {
       } while(change);
       getLog().append(program.getRegisterPotentials().toString());
 
-      // Find register uplift scopes
-      getLog().append("REGISTER UPLIFT SCOPES");
-      new Pass4RegisterUpliftScopeAnalysis(program).findScopes();
-      getLog().append(program.getRegisterUpliftProgram().toString((program.getVariableRegisterWeights())));
+      if(!optimizeMinimal) {
+         // Find register uplift scopes
+         getLog().append("REGISTER UPLIFT SCOPES");
+         new Pass4RegisterUpliftScopeAnalysis(program).findScopes();
+         getLog().append(program.getRegisterUpliftProgram().toString((program.getVariableRegisterWeights())));
 
-      // Attempt uplifting registers through a lot of combinations
-      //getLog().setVerboseUplift(true);
-      new Pass4RegisterUpliftCombinations(program).performUplift(upliftCombinations);
+         // Attempt uplifting registers through a lot of combinations
+         //getLog().setVerboseUplift(true);
+         new Pass4RegisterUpliftCombinations(program).performUplift(upliftCombinations);
 
-      //getLog().setVerboseUplift(true);
-      //new Pass4RegisterUpliftStatic(program).performUplift();
-      //getLog().setVerboseUplift(false);
+         //getLog().setVerboseUplift(true);
+         //new Pass4RegisterUpliftStatic(program).performUplift();
+         //getLog().setVerboseUplift(false);
 
-      // Attempt uplifting registers one at a time to catch remaining potential not realized by combination search
-      new Pass4RegisterUpliftRemains(program).performUplift(upliftCombinations);
+         // Attempt uplifting registers one at a time to catch remaining potential not realized by combination search
+         new Pass4RegisterUpliftRemains(program).performUplift(upliftCombinations);
+      }
 
       // Final register coalesce and finalization
       new Pass4ZeroPageCoalesceAssignment(program).coalesce();
diff --git a/src/main/java/dk/camelot64/kickc/KickC.java b/src/main/java/dk/camelot64/kickc/KickC.java
index 1efac1a0a..e162c39a1 100644
--- a/src/main/java/dk/camelot64/kickc/KickC.java
+++ b/src/main/java/dk/camelot64/kickc/KickC.java
@@ -54,6 +54,9 @@ public class KickC implements Callable<Void> {
    @CommandLine.Option(names = {"-Ouplift" }, description = "Optimization Option. Number of combinations to test when uplifting variables to registers in a scope. By default 100 combinations are tested.")
    private Integer optimizeUpliftCombinations = null;
 
+   @CommandLine.Option(names = {"-O0" }, description = "Optimization Option. Perform minimal optimization to increase the speed of the compiler.")
+   private boolean optimizeMinimal = false;
+
    @CommandLine.Option(names = {"-v" }, description = "Verbose output describing the compilation process")
    private boolean verbose= false;
 
@@ -158,6 +161,10 @@ public class KickC implements Callable<Void> {
             compiler.setUpliftCombinations(optimizeUpliftCombinations);
          }
 
+         if(optimizeMinimal) {
+            compiler.setOptimizeMinimal(true);
+         }
+         
          System.out.println("Compiling " + kcFile);
          Program program = null;
          try {
diff --git a/src/main/java/dk/camelot64/kickc/asm/AsmProgramStaticRegisterValues.java b/src/main/java/dk/camelot64/kickc/asm/AsmProgramStaticRegisterValues.java
index 8ed96dc8a..c220df035 100644
--- a/src/main/java/dk/camelot64/kickc/asm/AsmProgramStaticRegisterValues.java
+++ b/src/main/java/dk/camelot64/kickc/asm/AsmProgramStaticRegisterValues.java
@@ -141,6 +141,8 @@ public class AsmProgramStaticRegisterValues {
          }
          if(mnemnonic.equals("sta") && (addressingMode.equals(AsmAddressingMode.ZP) || addressingMode.equals(AsmAddressingMode.ABS))) {
             current.setaMem(instruction.getParameter());
+            if(instruction.getParameter().equals(current.getyMem())) current.setyMem(null);
+            if(instruction.getParameter().equals(current.getxMem())) current.setxMem(null);
          }
          if(mnemnonic.equals("ldx") && addressingMode.equals(AsmAddressingMode.IMM)) {
             current.setX(instruction.getParameter());
@@ -157,6 +159,8 @@ public class AsmProgramStaticRegisterValues {
          }
          if(mnemnonic.equals("stx") && (addressingMode.equals(AsmAddressingMode.ZP) || addressingMode.equals(AsmAddressingMode.ABS))) {
             current.setxMem(instruction.getParameter());
+            if(instruction.getParameter().equals(current.getyMem())) current.setyMem(null);
+            if(instruction.getParameter().equals(current.getaMem())) current.setaMem(null);
          }
          if(mnemnonic.equals("ldy") && addressingMode.equals(AsmAddressingMode.IMM)) {
             current.setY(instruction.getParameter());
@@ -172,7 +176,8 @@ public class AsmProgramStaticRegisterValues {
          }
          if(mnemnonic.equals("sty") && (addressingMode.equals(AsmAddressingMode.ZP) || addressingMode.equals(AsmAddressingMode.ABS))) {
             current.setyMem(instruction.getParameter());
-            current.setY(null);
+            if(instruction.getParameter().equals(current.getxMem())) current.setxMem(null);
+            if(instruction.getParameter().equals(current.getaMem())) current.setaMem(null);
          }
          if(mnemnonic.equals("txa")) {
             current.setA(current.getX());
diff --git a/src/main/java/dk/camelot64/kickc/passes/Pass4ZeroPageCoalesce.java b/src/main/java/dk/camelot64/kickc/passes/Pass4ZeroPageCoalesce.java
index 7b3206e03..13cc2a77d 100644
--- a/src/main/java/dk/camelot64/kickc/passes/Pass4ZeroPageCoalesce.java
+++ b/src/main/java/dk/camelot64/kickc/passes/Pass4ZeroPageCoalesce.java
@@ -2,8 +2,8 @@ package dk.camelot64.kickc.passes;
 
 import dk.camelot64.kickc.model.*;
 import dk.camelot64.kickc.model.symbols.Procedure;
-import dk.camelot64.kickc.model.symbols.ProgramScope;
 import dk.camelot64.kickc.model.symbols.Variable;
+import dk.camelot64.kickc.model.values.ProcedureRef;
 import dk.camelot64.kickc.model.values.ScopeRef;
 import dk.camelot64.kickc.model.values.SymbolRef;
 import dk.camelot64.kickc.model.values.VariableRef;
@@ -110,7 +110,7 @@ public class Pass4ZeroPageCoalesce extends Pass2Base {
     * @return True if the two equivalence classes can be coalesced into one without problems.
     */
    private static boolean canCoalesceThreads(LiveRangeEquivalenceClass ec1, LiveRangeEquivalenceClass ec2, Collection<ScopeRef> threadHeads, Program program) {
-      if(threadHeads.size()<=1) {
+      if(threadHeads.size() <= 1) {
          return true;
       }
       CallGraph callGraph = program.getCallGraph();
@@ -136,11 +136,18 @@ public class Pass4ZeroPageCoalesce extends Pass2Base {
       for(VariableRef varRef : equivalenceClass.getVariables()) {
          Variable variable = program.getScope().getVariable(varRef);
          ScopeRef scopeRef = variable.getScope().getRef();
-         Collection<ScopeRef> recursiveCallers = callGraph.getRecursiveCallers(scopeRef);
-         for(ScopeRef threadHead : threadHeads) {
-            if(recursiveCallers.contains(threadHead)) {
-               if(!threads.contains(threadHead)) {
-                  threads.add(threadHead);
+         if(scopeRef.equals(ScopeRef.ROOT)) {
+            ProcedureRef mainThreadHead = program.getScope().getProcedure(SymbolRef.MAIN_PROC_NAME).getRef();
+            if(!threads.contains(mainThreadHead)) {
+               threads.add(mainThreadHead);
+            }
+         } else {
+            Collection<ScopeRef> recursiveCallers = callGraph.getRecursiveCallers(scopeRef);
+            for(ScopeRef threadHead : threadHeads) {
+               if(recursiveCallers.contains(threadHead)) {
+                  if(!threads.contains(threadHead)) {
+                     threads.add(threadHead);
+                  }
                }
             }
          }