Improve performance of expression propagation (#435)

Making basicblock.__str__ return repr because its way cheaper

decompiler/structures/graphs/basicblock.py

@@ -43,8 +43,10 @@ def __iter__(self) -> Iterator[Instruction]:
         yield from self._instructions
 
     def __str__(self) -> str:
-        """Return a string representation of all instructions in the basic block."""
-        return "\n".join((f"{instruction}" for instruction in self))
+        """Return a string representation of the block"""
+        # Note: Returning a string representation of all instructions here can be pretty expensive.
+        # Because most code does not expect this, we choose to simply return the cheap repr instead.
+        return repr(self)
 
     def __repr__(self) -> str:
         """Return a debug representation of the block."""

decompiler/structures/graphs/restructuring_graph/transition_cfg.py

@@ -29,7 +29,7 @@ def __init__(self, address: int, ast: AbstractSyntaxTreeNode):
         self.ast: AbstractSyntaxTreeNode = ast
 
     def __str__(self) -> str:
-        """Return a string representation of all instructions in the basic block."""
+        """Return a string representation of the block"""
         return str(self.ast)
 
     def __repr__(self) -> str:

tests/structures/graphs/test_basicblock.py

@@ -117,7 +117,7 @@ def test_instruction_management(testblock: BasicBlock):
 
 
 def test_block_representations(testblock: BasicBlock):
-    assert str(testblock) == "\n".join(str(instruction) for instruction in testblock)
+    assert str(testblock) == "BasicBlock(0x539, len=5)"
     assert repr(testblock) == "BasicBlock(0x539, len=5)"