remove dead code originating from control flow propagation (#384)

src/cwe_checker_lib/src/intermediate_representation/project/propagate_control_flow.rs

 use crate::analysis::graph::{Edge, Graph, Node};
 use crate::intermediate_representation::*;
 use petgraph::graph::NodeIndex;
-use std::collections::{BTreeSet, HashMap};
+use petgraph::Direction::Incoming;
+use std::collections::{BTreeSet, HashMap, HashSet};
 
 /// The `propagate_control_flow` normalization pass tries to simplify the representation of
 /// sequences of if-else blocks that all have the same condition
@@ -13,15 +14,17 @@ use std::collections::{BTreeSet, HashMap};
 /// we look for sequences of (conditional) jumps where the final jump target is determined by the source of the first jump
 /// (because we know that the conditionals for all jumps evaluate to the same value along the sequence).
 /// For such a sequence we then retarget the destination of the first jump to the final jump destination of the sequence.
+/// Lastly, the newly bypassed blocks are considered dead code and are removed.
 pub fn propagate_control_flow(project: &mut Project) {
-    let extern_subs = project
+    let extern_subs: HashSet<Tid> = project
         .program
         .term
         .extern_symbols
         .keys()
         .cloned()
         .collect();
-    let cfg = crate::analysis::graph::get_program_cfg(&project.program, extern_subs);
+    let cfg = crate::analysis::graph::get_program_cfg(&project.program, extern_subs.clone());
+    let nodes_without_incoming_edges_at_beginning = get_nodes_without_incoming_edge(&cfg);
 
     let mut jmps_to_retarget = HashMap::new();
     for node in cfg.node_indices() {
@@ -71,6 +74,15 @@ pub fn propagate_control_flow(project: &mut Project) {
         }
     }
     retarget_jumps(project, jmps_to_retarget);
+
+    let cfg = crate::analysis::graph::get_program_cfg(&project.program, extern_subs);
+    let nodes_without_incoming_edges_at_end = get_nodes_without_incoming_edge(&cfg);
+
+    remove_new_orphaned_blocks(
+        project,
+        nodes_without_incoming_edges_at_beginning,
+        nodes_without_incoming_edges_at_end,
+    );
 }
 
 /// Insert the new target TIDs into jump instructions for which a new target was computed.
@@ -242,6 +254,33 @@ fn negate_condition(expr: Expression) -> Expression {
     }
 }
 
+/// Iterates the CFG and returns all node's blocks, that do not have an incoming edge.
+fn get_nodes_without_incoming_edge(cfg: &Graph) -> HashSet<Tid> {
+    let mut nodes_without_incoming_edges = HashSet::new();
+    for node in cfg.node_indices() {
+        if cfg.neighbors_directed(node, Incoming).next().is_none() {
+            nodes_without_incoming_edges.insert(cfg[node].get_block().tid.clone());
+        }
+    }
+    nodes_without_incoming_edges
+}
+
+/// Calculates the difference of the orphaned blocks and removes them from the project.
+fn remove_new_orphaned_blocks(
+    project: &mut Project,
+    orphaned_blocks_before: HashSet<Tid>,
+    orphaned_blocks_after: HashSet<Tid>,
+) {
+    let new_orphan_blocks: HashSet<&Tid> = orphaned_blocks_after
+        .difference(&orphaned_blocks_before)
+        .collect();
+    for sub in project.program.term.subs.values_mut() {
+        sub.term
+            .blocks
+            .retain(|blk| !new_orphan_blocks.contains(&&blk.tid));
+    }
+}
+
 #[cfg(test)]
 pub mod tests {
     use super::*;
@@ -251,7 +290,7 @@ pub mod tests {
     fn mock_condition_block(name: &str, if_target: &str, else_target: &str) -> Term<Blk> {
         let if_jmp = Jmp::CBranch {
             target: Tid::new(if_target),
-            condition: expr!("zero_flag:1"),
+            condition: expr!("ZF:1"),
         };
         let if_jmp = Term {
             tid: Tid::new(name.to_string() + "_jmp_if"),
@@ -275,7 +314,6 @@ pub mod tests {
 
     fn mock_block_with_defs(name: &str, return_target: &str) -> Term<Blk> {
         let def = def![format!("{name}_def: r0:4 = r1:4")];
-
         let jmp = Jmp::Branch(Tid::new(return_target));
         let jmp = Term {
             tid: Tid::new(name.to_string() + "_jmp"),
@@ -318,9 +356,9 @@ pub mod tests {
         let expected_blocks = vec![
             mock_condition_block("cond_blk_1", "def_blk_1", "end_blk"),
             mock_block_with_defs("def_blk_1", "def_blk_2"),
-            mock_condition_block("cond_blk_2", "def_blk_2", "end_blk"),
+            // cond_blk_2 removed, since no incoming edge anymore
             mock_block_with_defs("def_blk_2", "def_blk_3"),
-            mock_condition_block("cond_blk_3", "def_blk_3", "end_blk"),
+            // cond_blk_3 removed, since no incoming edge anymore
             mock_block_with_defs("def_blk_3", "end_blk"),
             mock_block_with_defs("end_blk", "end_blk"),
         ];