Some fixes, tests and updated README

optvm/README.md

@@ -44,11 +44,14 @@ A VM / Interpreter is provided that can run the generated code.
   SSA Form using Dominator Trees. The input to this transformation is regular IR, output is SSA IR.
 * Incremental SSA - This method generate SSA IR directly from the AST, using [Braun's algorithm](https://dl.acm.org/doi/10.1007/978-3-642-37051-9_6) - this is integrated into the
   [compiler](src/main/java/com/compilerprogramming/ezlang/compiler/CompiledFunction.java) itself and can be enabled using an option.
-* [ExitSSA](src/main/java/com/compilerprogramming/ezlang/compiler/ExitSSA.java) - Exits SSA form, using algorithm by Preston Briggs.
+* [ExitSSA](src/main/java/com/compilerprogramming/ezlang/compiler/ExitSSA.java) - Exits SSA form - i.e. implements SSA destruction. Two methods are implemented:
+  * [ExitSSABriggs](src/main/java/com/compilerprogramming/ezlang/compiler/ExitSSABriggs.java) - implements method described by [Preston Briggs](https://dl.acm.org/doi/10.5555/295545.295551).
+  * [ExitSSABoissinotNoCoalesce](src/main/java/com/compilerprogramming/ezlang/compiler/ExitSSABoissinotNoCoalesce.java) - implements method described by [Benoit Boissinot](https://inria.hal.science/inria-00349925v1/document) - 
+    without the coalescing step. Thus, it is the "naive" approach that resembles Sreedhar's method I. 
 
 ## Optimizations on SSA Form
 
-* [SparseConditionalConstantPropagation](src/main/java/com/compilerprogramming/ezlang/compiler/SparseConditionalConstantPropagation.java) - Conditional Constant Propagation on SSA form (SCCP)
+* [SparseConditionalConstantPropagation](src/main/java/com/compilerprogramming/ezlang/compiler/SparseConditionalConstantPropagation.java) - Conditional Constant Propagation on SSA form (SCCP). This is an implementation of the paper [Constant propagation with conditional branches](https://dl.acm.org/doi/10.1145/103135.103136).
 * [ConstantComparisonPropagation](src/main/java/com/compilerprogramming/ezlang/compiler/ConstantComparisonPropagation.java) - Detects equals and not equals against constants within conditionals,
    and inserts scoped variables with appropriately specialized type within the dominated blocks, so that a second pass of SCCP can further optimize code.
 * [SSAEdges](src/main/java/com/compilerprogramming/ezlang/compiler/SSAEdges.java) - SSAEdges are def-use chains used by SCCP algorithm, and also generated during incremental SSA construction using Braun's method.
@@ -70,7 +73,7 @@ unlimited amount of those.
 * [InterferenceGraphBuilder](src/main/java/com/compilerprogramming/ezlang/compiler/InterferenceGraphBuilder.java) - Constructs an InterferenceGraph for a set
   of basic bocks, using basic block level liveness information as a starting point for calculating instruction level liveness.
 * [ChaitinGraphColoringRegisterAllocator](src/main/java/com/compilerprogramming/ezlang/compiler/ChaitinGraphColoringRegisterAllocator.java) - basic
-  Chaitin Graph Coloring Register Allocator. Since our target machine here is an abstract machine, we do not really needing spilling support
+  [Chaitin Graph Coloring Register Allocator](https://web.eecs.umich.edu/~mahlke/courses/583f12/reading/chaitin82.pdf) without spilling. Since our target machine here is an abstract machine, we do not really need spilling support
   as we can size each function's stack frame to accommodate the number of registers needed such that each register is really a slot in the stack
   frame. But we will eventually simulate an abstract machine with a limited set of registers and a separate stack frame.
 

optvm/src/main/java/com/compilerprogramming/ezlang/compiler/CompiledFunction.java

@@ -27,6 +27,8 @@ public class CompiledFunction {
     public boolean hasLiveness;
     private final IncrementalSSA issa;
 
+    private StringBuilder dumpTarget;
+
     /**
      * We essentially do a form of abstract interpretation as we generate
      * the bytecode instructions. For this purpose we use a virtual operand stack.
@@ -72,7 +74,9 @@ public CompiledFunction(EZType.EZTypeFunction functionType, TypeDictionary typeD
         issa.finish(null);
         this.frameSlots = registerPool.numRegisters();
     }
-
+    public void setDumpTarget(StringBuilder dumpTarget) {
+        this.dumpTarget = dumpTarget;
+    }
     private void generateArgInstructions(Scope scope) {
         if (scope.isFunctionParameterScope) {
             for (Symbol symbol: scope.getLocalSymbols()) {
@@ -814,8 +818,14 @@ public StringBuilder toStr(StringBuilder sb, boolean verbose) {
     }
 
     public void dumpIR(boolean verbose, String title) {
-        System.out.println(title);
-        System.out.println(toStr(new StringBuilder(), verbose));
+        if (dumpTarget != null) {
+            dumpTarget.append(title).append("\n");
+            toStr(dumpTarget,verbose);
+        }
+        else {
+            System.out.println(title);
+            System.out.println(toStr(new StringBuilder(), verbose));
+        }
     }
 
     public void livenessAnalysis() {

optvm/src/main/java/com/compilerprogramming/ezlang/compiler/ExitSSABoissinotNoCoalesce.java

@@ -41,10 +41,12 @@ public ExitSSABoissinotNoCoalesce(CompiledFunction function, EnumSet<Options> op
         allBlocks = function.getBlocks();
         init();
         makeConventionalSSA();
+        if (options.contains(Options.DUMP_SSA_TO_CSSA)) function.dumpIR(false, "After converting from SSA to CSSA");
         removePhis();
+        if (options.contains(Options.DUMP_CSSA_PHI_REMOVAL)) function.dumpIR(false, "After removing phis from CSSA");
         sequenceParallelCopies();
         function.isSSA = false;
-        if (options.contains(Options.DUMP_POST_SSA_IR)) function.dumpIR(false, "After exiting SSA");
+        if (options.contains(Options.DUMP_POST_SSA_IR)) function.dumpIR(false, "After exiting SSA (Boissinot method)");
     }
 
     private void init() {

optvm/src/main/java/com/compilerprogramming/ezlang/compiler/InterferenceGraph.java

@@ -62,6 +62,12 @@ public boolean interfere(Integer from, Integer to) {
     public void rename(Integer source, Integer target) {
         // Move all interferences
         var fromSet = edges.remove(source);
+        if (fromSet == null) {
+            // FIXME figure out why
+            // Test case testSSA21 / when run using Boissinot SSA Destruction without coalescing
+            // This is eq() function in mergesort test case
+            return;
+        }
         var toSet = edges.get(target);
         if (toSet == null) {
             //throw new RuntimeException("Cannot find edge " + target + " from " + source);

optvm/src/main/java/com/compilerprogramming/ezlang/compiler/Options.java

@@ -20,14 +20,18 @@ public enum Options {
     DUMP_CCP_POSTAPPLY,
     DUMP_SSA_LIVENESS,
     DUMP_SSA_DOMTREE,
+    DUMP_SSA_TO_CSSA,
+    DUMP_CSSA_PHI_REMOVAL,
     DUMP_POST_SSA_IR,
     DUMP_INTERFERENCE_GRAPH,
     DUMP_CHAITIN_COALESCE,
     DUMP_POST_CHAITIN_IR;
 
     public static final EnumSet<Options> NONE = EnumSet.noneOf(Options.class);
     public static final EnumSet<Options> OPT = EnumSet.of(Options.OPTIMIZE,Options.SCCP,Options.CCP,Options.REGALLOC);
+    public static final EnumSet<Options> OPT_B = EnumSet.of(Options.OPTIMIZE,Options.SCCP,Options.CCP,Options.REGALLOC,Options.SSA_DESTRUCTION_BOISSINOT_NOCOALESCE);
     public static final EnumSet<Options> OPT_ISSA = EnumSet.of(Options.OPTIMIZE,Options.ISSA,Options.SCCP,Options.CCP,Options.REGALLOC);
+    public static final EnumSet<Options> OPT_ISSA_B = EnumSet.of(Options.OPTIMIZE,Options.ISSA,Options.SCCP,Options.CCP,Options.REGALLOC,Options.SSA_DESTRUCTION_BOISSINOT_NOCOALESCE);
     public static final EnumSet<Options> VERBOSE = EnumSet.range(DUMP_INITIAL_IR, DUMP_POST_CHAITIN_IR);
     public static final EnumSet<Options> OPT_VERBOSE = EnumSet.range(OPTIMIZE, DUMP_POST_CHAITIN_IR);
 }