Bug fixes

README.md

@@ -26,8 +26,9 @@ The project is under development and subject to change. At this point in time, w
 * [semantic](./semantic/README.md) - semantic analyzer
 * [stackvm](./stackvm/README.md) - a compiler that generates IR for a stack based virtual machine
 * [registervm](./registervm/README.md) - a compiler that generates a so called three-address IR and an interpreter that can execute the IR
-* [optvm](./optvm/README.md) - an optimizing compiler (WIP) that supports SSA.
-* [seaofnodes](./seaofnodes/README.md) - a compiler that will generate Sea of Nodes IR, using SoN backend from [Simple](https://github.com/SeaOfNodes/Simple).
+* [optvm](./optvm/README.md) - WIP optimizing compiler with SSA transformation, constant propagation, graph coloring register allocation 
+  targeting an abstract machine.
+* [seaofnodes](./seaofnodes/README.md) - WIP compiler that generates Sea of Nodes IR, using SoN backend from [Simple](https://github.com/SeaOfNodes/Simple).
 
 ## How can you contribute?
 

optvm/README.md

@@ -33,10 +33,14 @@ a physical machine. Therefore, all our optimization passes will work on the inst
   each register has a unique integer ID and these ids are allocated in a sequential manner.
 * [Liveness](src/main/java/com/compilerprogramming/ezlang/compiler/Liveness.java) - Liveness calculator, works for both SSA and non-SSA forms. Computes
   liveness data per basic block - mainly live-out. Note that the interference graph builder starts here and computes instruction level liveness as necessary.
-* [EnterSSA](src/main/java/com/compilerprogramming/ezlang/compiler/EnterSSA.java) - Transforms into SSA, using algorithm by Preston Briggs.
+* [EnterSSA](src/main/java/com/compilerprogramming/ezlang/compiler/EnterSSA.java) - Transforms into SSA, using [algorithm by Preston Briggs](https://dl.acm.org/doi/10.5555/295545.295551). This is one of available mechanisms to transform the IR into SSA. 
+  The other alternative is to generate SSA IR directly from the AST, using [Braun's method](https://dl.acm.org/doi/10.1007/978-3-642-37051-9_6) - this option is integrated into the
+  [compiler]((src/main/java/com/compilerprogramming/ezlang/compiler/CompiledFunction.java)) and enabled using an option.
 * [ExitSSA](src/main/java/com/compilerprogramming/ezlang/compiler/ExitSSA.java) - Exits SSA form, using algorithm by Preston Briggs.
 * [SparseConditionalConstantPropagation](src/main/java/com/compilerprogramming/ezlang/compiler/SparseConditionalConstantPropagation.java) - Conditional Constant Propagation on SSA form (SCCP)
-* [SSAEdges](src/main/java/com/compilerprogramming/ezlang/compiler/SSAEdges.java) - SSAEdges are def-use chains used by SCCP algorithm 
+* [ConstantComparisonPropagation](src/main/java/com/compilerprogramming/ezlang/compiler/ConstantComparisonPropagation.java) - Detects equals and not equals against constants within conditionals,
+   and inserts 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.
 * [LoopFinder](src/main/java/com/compilerprogramming/ezlang/compiler/LoopFinder.java) - Discovers loops. (Not used yet)
 * [LoopNest](src/main/java/com/compilerprogramming/ezlang/compiler/LoopNest.java) - Representation of loop nesting. (Not used yet)
 * [InterferenceGraph](src/main/java/com/compilerprogramming/ezlang/compiler/InterferenceGraph.java) - Representation of an Interference Graph

optvm/src/test/java/com/compilerprogramming/ezlang/interpreter/TestInterpreter.java

@@ -613,7 +613,7 @@ public void testMergeSort() {
         String src = """
 // based on the top-down version from https://en.wikipedia.org/wiki/Merge_sort
 // via https://github.com/SeaOfNodes/Simple
-func merge_sort(a: [Int], b: [int], n: Int) 
+func merge_sort(a: [Int], b: [Int], n: Int) 
 {
     copy_array(a, 0, n, b)
     split_merge(a, 0, n, b)

registervm/src/test/java/com/compilerprogramming/ezlang/interpreter/TestInterpreter.java

@@ -250,7 +250,7 @@ public void testMergeSort() {
         String src = """
 // based on the top-down version from https://en.wikipedia.org/wiki/Merge_sort
 // via https://github.com/SeaOfNodes/Simple
-func merge_sort(a: [Int], b: [int], n: Int) 
+func merge_sort(a: [Int], b: [Int], n: Int) 
 {
     copy_array(a, 0, n, b)
     split_merge(a, 0, n, b)

seaofnodes/src/main/java/com/compilerprogramming/ezlang/compiler/Compiler.java

@@ -941,7 +941,11 @@ private Node compileLet(AST.VarStmt letStmt) {
     }
 
     private Node compileReturn(AST.ReturnStmt returnStmt) {
-        var expr = compileExpr(returnStmt.expr);
+        Node expr;
+        if (returnStmt.expr != null)
+            expr = compileExpr(returnStmt.expr);
+        else
+            expr = ZERO;
         // Need default memory, since it can be lazy, need to force
         // a non-lazy Phi
         _fun.addReturn(ctrl(), _scope.mem().merge(), expr);