Lazily define object parameter constants which are needed by the Stac…

…kMapTable attribute, in case the attribute isn't needed at all.

CHANGELOG.md

@@ -5,6 +5,7 @@ v2.5.11
 -------
 * Added a variable decrement method.
 * Avoid generating a conversion instruction when comparing against a constant primitive value.
+* Reduce constant pool pollution when the StackMapTable attribute isn't needed.
 
 v2.5.10 (2024-08-07)
 -------

src/main/java/org/cojen/maker/StackMapTable.java

@@ -26,17 +26,15 @@
  * @author Brian S O'Neill
  */
 class StackMapTable extends Attribute {
-    private final Frame mInitFrame;
     private Frame mFirstFrame, mLastFrame;
     private int mNumFrames;
     private BytesOut mFinished;
 
     /**
      * @param initCodes can be null
      */
-    StackMapTable(ConstantPool cp, int[] initCodes) {
+    StackMapTable(ConstantPool cp) {
         super(cp); // set the name later; see finish()
-        mInitFrame = new Frame(Integer.MIN_VALUE, initCodes, null);
     }
 
     /**
@@ -80,19 +78,34 @@ void reset() {
     /**
      * @return false if table is empty and should not be written
      */
-    boolean finish() {
+    boolean finish(TheMethodMaker.ParamVar[] params) {
         if (mFirstFrame == null) {
             return false;
         }
 
         // Lazily set the name such that it's added to the ConstantPool only when needed.
         name("StackMapTable");
 
+        // Make the initial frame to represent the method parameters.
+        Frame prev;
+        {
+            int[] initCodes;
+            if (params.length == 0) {
+                initCodes = null;
+            } else {
+                initCodes = new int[params.length];
+                for (int i=0; i<initCodes.length; i++) {
+                    initCodes[i] = params[i].smCodeInit();
+                }
+            }
+
+            prev = new Frame(Integer.MIN_VALUE, initCodes, null);
+        }
+
         var out = new BytesOut(null, mNumFrames * 4);
 
         try {
             out.writeShort(mNumFrames);
-            Frame prev = mInitFrame;
             Frame frame = mFirstFrame;
             do {
                 frame.writeTo(prev, out);

src/main/java/org/cojen/maker/TheMethodMaker.java

@@ -198,22 +198,9 @@ void doFinish() {
 
         mVars = varList.toArray(new LocalVar[varList.size()]);
 
-        // Prepare the StackMapTable.
-        {
-            Arrays.sort(mVars); // sort by slot
-
-            int[] initCodes;
-            if (mParams.length == 0) {
-                initCodes = null;
-            } else {
-                initCodes = new int[mParams.length];
-                for (int i=0; i<initCodes.length; i++) {
-                    initCodes[i] = mParams[i].smCode();
-                }
-            }
+        Arrays.sort(mVars); // sort by slot, as required by Lab.appendTo
 
-            mStackMapTable = new StackMapTable(mConstants, initCodes);
-        }
+        mStackMapTable = new StackMapTable(mConstants);
 
         mCode = new byte[Math.min(MAX_CODE_LENGTH, opCount * 2)];
         mStack = new LocalVar[8];
@@ -257,7 +244,6 @@ void doFinish() {
             new Flow(varList, varUsage).run(mFirstOp);
         }
 
-        mParams = null;
         mFirstOp = null;
         mLastOp = null;
         mReturnLabel = null;
@@ -277,11 +263,13 @@ void doFinish() {
 
         mExceptionHandlers = null;
 
-        if (mStackMapTable.finish()) {
+        if (mStackMapTable.finish(mParams)) {
             codeAttr.addAttribute(mStackMapTable);
             mStackMapTable = null;
         }
 
+        mParams = null;
+
         if (mLineNumberTable != null && mLineNumberTable.finish(mCodeLen)) {
             codeAttr.addAttribute(mLineNumberTable);
         }
@@ -5378,6 +5366,13 @@ class ParamVar extends LocalVar {
             mIndex = index;
         }
 
+        /**
+         * Needed for StackMapTable. Returns the SM code at the start of the method.
+         */
+        int smCodeInit() {
+            return smCode();
+        }
+
         @Override
         public LocalVar name(String name) {
             super.name(name);
@@ -5560,6 +5555,11 @@ int smCode() {
             return mSmCode;
         }
 
+        @Override
+        int smCodeInit() {
+            return SM_UNINIT_THIS;
+        }
+
         void ready() {
             if (mSmCode != SM_UNINIT_THIS) {
                 throw finishFail("Super or this constructor invoked multiple times");