Chaitin Graph Coloring Register allocator - WIP coalesce step

Chaitin Graph Coloring Register allocator - WIP coalesce step

Bugfix

Bugfix

Phi and liveness issue
Refactored Instruction so that we avoid calculating uses all over the place

Some unit tests

Author: dibyendumajumdar

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

@@ -0,0 +1,57 @@
+package com.compilerprogramming.ezlang.compiler;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class ChaitinGraphColoringRegisterAllocator {
+
+    public ChaitinGraphColoringRegisterAllocator(CompiledFunction function) {
+        coalesce(function);
+    }
+
+    private void coalesce(CompiledFunction function) {
+        boolean changed = true;
+        while (changed) {
+            var igraph = new InterferenceGraphBuilder().build(function);
+            changed = coalesceRegisters(function, igraph);
+        }
+    }
+
+    private boolean coalesceRegisters(CompiledFunction function, InterferenceGraph igraph) {
+        boolean changed = false;
+        for (var block: function.getBlocks()) {
+            List<Integer> instructionsToRemove = new ArrayList<>();
+            for (int j = 0; j < block.instructions.size(); j++) {
+                Instruction i = block.instructions.get(j);
+                if (i instanceof Instruction.Move move
+                    && move.from() instanceof Operand.RegisterOperand targetOperand) {
+                    Register source = move.def();
+                    Register target = targetOperand.reg;
+                    if (source.id != target.id &&
+                        !igraph.interfere(target.id, source.id)) {
+                        igraph.rename(source.id, target.id);
+                        rewriteInstructions(function, i, source, target);
+                        instructionsToRemove.add(j);
+                        changed = true;
+                    }
+                }
+            }
+            for (var j: instructionsToRemove) {
+                block.instructions.set(j, new Instruction.NoOp());
+            }
+        }
+        return changed;
+    }
+
+    private void rewriteInstructions(CompiledFunction function, Instruction notNeeded, Register source, Register target) {
+        for (var block: function.getBlocks()) {
+            for (Instruction i: block.instructions) {
+                if (i == notNeeded)
+                    continue;
+                if (i.definesVar() && source.id == i.def().id)
+                    i.replaceDef(target);
+                i.replaceUse(source, target);
+            }
+        }
+    }
+}

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

@@ -565,4 +565,8 @@ public void livenessAnalysis() {
         new Liveness(this);
         this.hasLiveness = true;
     }
+
+    public List<BasicBlock> getBlocks() {
+        return BBHelper.findAllBlocks(entry);
+    }
 }

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

@@ -18,6 +18,7 @@ public ExitSSA(CompiledFunction function) {
         this.function = function;
         if (!function.isSSA) throw new IllegalStateException();
         function.livenessAnalysis();
+        System.out.println(function.toStr(new StringBuilder(), true));
         tree = new DominatorTree(function.entry);
         initStack();
         insertCopies(function.entry);
@@ -35,9 +36,7 @@ private void insertCopies(BasicBlock block) {
         List<Integer> pushed = new ArrayList<>();
         for (Instruction i: block.instructions) {
             // replace all uses u with stacks[i]
-            if (i.usesVars()) {
-                replaceUses(i);
-            }
+            replaceUses(i);
         }
         scheduleCopies(block, pushed);
         for (BasicBlock c: block.dominatedChildren) {
@@ -86,7 +85,7 @@ private void scheduleCopies(BasicBlock block, List<Integer> pushed) {
             int j = SSATransform.whichPred(s, block);
             for (Instruction.Phi phi: s.phis()) {
                 Register dst = phi.def();
-                Register src = phi.inputs.get(j).reg;   // jth operand of phi node
+                Register src = phi.input(j);   // jth operand of phi node
                 copySet.add(new CopyItem(src, dst));
                 map.put(src.id, src);
                 map.put(dst.id, dst);