From 634917f280f7e8576c9453c671cc87481fa10653 Mon Sep 17 00:00:00 2001
From: Andrei Homescu <ah@immunant.com>
Date: Thu, 13 Jun 2024 00:41:07 -0700
Subject: [PATCH] Build PDG without tracking assignments

The event assignment-based PDG
construction steps were giving incorrect results
for indirect accesses, so remove them completely.
---
 pdg/src/builder.rs | 61 +++++++++-------------------------------------
 1 file changed, 12 insertions(+), 49 deletions(-)

diff --git a/pdg/src/builder.rs b/pdg/src/builder.rs
index c290b46f8..467ceff29 100644
--- a/pdg/src/builder.rs
+++ b/pdg/src/builder.rs
@@ -122,7 +122,7 @@ fn update_provenance(
         Realloc { new_ptr, .. } => {
             provenances.insert(new_ptr, mapping);
         }
-        Offset(_, _, new_ptr) => {
+        Offset(_, _, new_ptr) | Project(_, new_ptr, _) => {
             provenances.insert(new_ptr, mapping);
         }
         CopyRef => {
@@ -151,7 +151,7 @@ pub fn add_node(
 
     let node_kind = event.kind.to_node_kind(func.id, address_taken)?;
     let this_id = func.id;
-    let (src_fn, dest_fn) = match event_metadata.transfer_kind {
+    let (_src_fn, dest_fn) = match event_metadata.transfer_kind {
         TransferKind::None => (this_id, this_id),
         TransferKind::Arg(id) => (this_id, id),
         TransferKind::Ret(id) => (id, this_id),
@@ -173,37 +173,22 @@ pub fn add_node(
             .iter()
             .rposition(|n| {
                 if let (Some(d), Some(s)) = (&n.dest, &event_metadata.source) {
-                    d == s
+                    // TODO: Ignore direct assignments with projections for now,
+                    // e.g., `_1.0 = _2;`. We should later add support for
+                    // assignments to sub-fields, e.g.
+                    // ```
+                    //   _1 = _2;
+                    //   _1.0 = _3;
+                    //   _1 = _4;
+                    // ```
+                    d == s && s.projection.is_empty()
                 } else {
                     false
                 }
             })
             .map(|nid| (gid, NodeId::from(nid)))
     });
-
-    let source = direct_source.or_else(|| {
-        event_metadata.source.as_ref().and_then(|src| {
-            let latest_assignment = graphs.latest_assignment.get(&(src_fn, src.local)).cloned();
-            if !src.projection.is_empty() {
-                if let Some((gid, _)) = latest_assignment {
-                    if let Some((nid, n)) = graphs.graphs[gid].nodes.iter_enumerated().rev().next()
-                    {
-                        if let NodeKind::Project(..) = n.kind {
-                            return Some((gid, nid));
-                        }
-                    }
-                }
-            }
-
-            if !matches!(event.kind, EventKind::AddrOfLocal(..)) && src.projection.is_empty() {
-                latest_assignment
-            } else if let EventKind::Project(..) = event.kind {
-                latest_assignment
-            } else {
-                provenance
-            }
-        })
-    });
+    let source = direct_source.or(provenance);
 
     let function = Func {
         id: dest_fn,
@@ -224,8 +209,6 @@ pub fn add_node(
     };
 
     let graph_id = source
-        .or(direct_source)
-        .or(provenance)
         .and_then(|p| parent(&node_kind, p))
         .map(|(gid, _)| gid)
         .unwrap_or_else(|| graphs.graphs.push(Graph::new()));
@@ -238,26 +221,6 @@ pub fn add_node(
         (graph_id, node_id),
     );
 
-    if let Some(dest) = &event_metadata.destination {
-        let unique_place = (dest_fn, dest.local);
-        let last_setting = (graph_id, node_id);
-
-        if let Some(last @ (last_gid, last_nid)) =
-            graphs.latest_assignment.insert(unique_place, last_setting)
-        {
-            if !dest.projection.is_empty()
-                && graphs.graphs[last_gid].nodes[last_nid]
-                    .dest
-                    .as_ref()
-                    .unwrap()
-                    .projection
-                    .is_empty()
-            {
-                graphs.latest_assignment.insert(unique_place, last);
-            }
-        }
-    }
-
     Some(node_id)
 }