Fix uncached backward-branch threshold generation

Author: steve-s

truffle/src/com.oracle.truffle.api.bytecode.test/src/com/oracle/truffle/api/bytecode/test/basic_interpreter/BasicInterpreterTest.java

@@ -2575,8 +2575,8 @@ public void testTransitionToCachedLoop() {
 
         node.getBytecodeNode().setUncachedThreshold(10);
         assertEquals(BytecodeTier.UNCACHED, node.getBytecodeNode().getTier());
-        // 1 call + 9 backedges causes on-stack transition to cached.
-        assertEquals(9L, node.getCallTarget().call());
+        // 1 call + 10 backedges causes on-stack transition to cached.
+        assertEquals(10L, node.getCallTarget().call());
         assertEquals(BytecodeTier.CACHED, node.getBytecodeNode().getTier());
     }
 

truffle/src/com.oracle.truffle.dsl.processor/src/com/oracle/truffle/dsl/processor/bytecode/generator/BytecodeInstructionHandler.java

@@ -790,7 +790,7 @@ private TypeMirror emitBranchBackward(CodeTreeBuilder b) {
 
                 b.end();
             } else {
-                b.startIf().string("uncachedExecuteCount_ <= 1").end().startBlock();
+                b.startIf().string("uncachedExecuteCount_ <= 0").end().startBlock();
                 /*
                  * The force uncached check is put in here so that we don't need to check it in the
                  * common case (the else branch where we just decrement).
@@ -858,7 +858,7 @@ private void emitBranchBackwardCaseBlock(CodeTreeBuilder b) {
         if (getTier().isUncached()) {
             b.statement("bci = " + BytecodeRootNodeElement.readImmediate("bc", "bci", instruction.getImmediate(ImmediateKind.BYTECODE_INDEX)));
 
-            b.startIf().string("uncachedExecuteCount_ <= 1").end().startBlock();
+            b.startIf().string("uncachedExecuteCount_ <= 0").end().startBlock();
             /*
              * The force uncached check is put in here so that we don't need to check it in the
              * common case (the else branch where we just decrement).