Wasm: fix issue with attempt to shrink heap after GC

core/src/main/java/org/teavm/backend/c/intrinsic/GCIntrinsic.java

@@ -39,6 +39,7 @@ public class GCIntrinsic implements Intrinsic {
             case "resizeHeap":
             case "cardTable":
             case "writeBarrier":
+            case "canShrinkHeap":
                 return true;
             default:
                 return false;
@@ -60,6 +61,10 @@ public class GCIntrinsic implements Intrinsic {
                 context.writer().print(")");
                 break;
 
+            case "canShrinkHeap":
+                context.writer().print("1");
+                break;
+
             default:
                 context.includes().includePath("heaptrace.h");
                 context.writer().print("teavm_gc_").print(invocation.getMethod().getName());

core/src/main/java/org/teavm/backend/wasm/intrinsics/GCIntrinsic.java

@@ -72,6 +72,7 @@ public class GCIntrinsic implements WasmIntrinsic {
             case "maxAvailableBytes":
             case "resizeHeap":
             case "writeBarrier":
+            case "canShrinkHeap":
                 return true;
             default:
                 return false;
@@ -131,6 +132,12 @@ public class GCIntrinsic implements WasmIntrinsic {
                         cardIndex);
                 return new WasmStoreInt32(1, card, new WasmInt32Constant(0), WasmInt32Subtype.INT8);
             }
+            case "canShrinkHeap": {
+                var expr = new WasmInt32Constant(0);
+                expr.setLocation(invocation.getLocation());
+                return expr;
+            }
+
             default:
                 throw new IllegalArgumentException(invocation.getMethod().toString());
         }

core/src/main/java/org/teavm/runtime/GC.java

@@ -67,6 +67,8 @@ public final class GC {
 
     public static native void resizeHeap(long size);
 
+    public static native boolean canShrinkHeap();
+
     private static native int regionSize();
 
     public static native void writeBarrier(RuntimeObject object);
@@ -183,7 +185,8 @@ public final class GC {
         }
 
         if (!isFullGC) {
-            if (++youngGCCount >= 8 && isAboutToExpand(minRequestedSize)) {
+            var youngGCLimit = canShrinkHeap() ? 2 : 8;
+            if (++youngGCCount >= youngGCLimit && isAboutToExpand(minRequestedSize)) {
                 triggerFullGC();
                 doCollectGarbage();
                 youngGCCount = 0;
@@ -1387,7 +1390,7 @@ public final class GC {
                 freeChunks++;
                 totalChunks++;
             }
-        } else {
+        } else if (canShrinkHeap()) {
             long minimumSize = lastChunk.toAddress().toLong() - heapAddress().toLong();
             if (lastChunk.classReference != 0) {
                 minimumSize += objectSize(lastChunk);