Avoid creating new basic block unless we break to it

Summary: This is similar to D81642076, we need to avoid creating a basic block to make sure other analysis passes proceed the same. This one is a little more complicated because it depends on their being a break to create the jump to the block.

Reviewed By: jbower-fb

Differential Revision: D81731244

fbshipit-source-id: 405bfc33533a350c6aac6798a302e1db583d4883

Author: DinoV

cinderx/PythonLib/cinderx/compiler/pycodegen.py

@@ -6425,6 +6425,49 @@ def _compile_async_comprehension(
         self.set_pos(comp)
         self.emit("END_ASYNC_FOR", send)
 
+    def visitBreak(self, node: ast.Break) -> None:
+        self.emit("NOP")  # for line number
+        loop = self.unwind_setup_entries(preserve_tos=False, stop_on_loop=True)
+        if loop is None:
+            raise self.syntax_error("'break' outside loop", node)
+        self.unwind_setup_entry(loop, preserve_tos=False)
+
+        jumpblock = loop.exit
+        if jumpblock is None:
+            loop.exit = jumpblock = self.newBlock("break")
+
+        self.emitJump(jumpblock)
+        self.nextBlock()
+
+    def visitFor(self, node: ast.For) -> None:
+        start = self.newBlock("for_start")
+        body = self.newBlock("for_body")
+        cleanup = self.newBlock("for_cleanup")
+
+        setup = Entry(FOR_LOOP, start, None, None)
+        self.push_fblock(setup)
+        self.visit(node.iter)
+        self.set_pos(node.iter)
+        self.emit("GET_ITER")
+
+        self.nextBlock(start)
+        self.emit("FOR_ITER", cleanup)
+        if IS_3_12_8:
+            self.graph.emit_with_loc("NOP", 0, node.target)
+        self.nextBlock(body)
+        self.visit(node.target)
+        self.visitStatements(node.body)
+        self.set_no_pos()
+        self.emitJump(start)
+        self.nextBlock(cleanup)
+        self.emit_end_for()
+        self.pop_loop()
+
+        if node.orelse:
+            self.visitStatements(node.orelse)
+        if setup.exit is not None:
+            self.nextBlock(setup.exit)
+
     def visitFormattedValue(self, node: ast.FormattedValue) -> None:
         self.visit(node.value)
 

cinderx/PythonLib/test_cinderx/test_compiler/testcorpus/16_for_try_except.py

@@ -0,0 +1,9 @@
+# pyre-ignore-all-errors
+def f():
+    try:
+        for el in x:
+            break
+    except Exception:
+        pass
+
+    foo()