From 94447748954bc02298d494527d019556908762fe Mon Sep 17 00:00:00 2001
From: Chris Smowton <smowton@github.com>
Date: Tue, 16 Mar 2021 10:45:25 +0000
Subject: [PATCH] Add further hints that the range of possible addressed
 fields, and therefore the interesting selector expressions, are small

---
 .../go/controlflow/ControlFlowGraphImpl.qll      | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/ql/src/semmle/go/controlflow/ControlFlowGraphImpl.qll b/ql/src/semmle/go/controlflow/ControlFlowGraphImpl.qll
index 07a043bdce0..70685046777 100644
--- a/ql/src/semmle/go/controlflow/ControlFlowGraphImpl.qll
+++ b/ql/src/semmle/go/controlflow/ControlFlowGraphImpl.qll
@@ -48,13 +48,13 @@ private predicate isCond(Expr e) {
   e = any(ParenExpr par | isCond(par)).getExpr()
 }
 
-private class PromotedField extends Field {
-  PromotedField() { this = any(StructType t).getFieldOfEmbedded(_, _, _, _) }
+private Type getSelectedStructType(PromotedFieldSelector e) {
+  pragma[only_bind_into](result) = e.getBase().getType().getBaseType*().getUnderlyingType()
 }
 
-private predicate implicitFieldSelection(SelectorExpr e, int i, Field implicitField) {
+private predicate implicitFieldSelection(PromotedFieldSelector e, int i, Field implicitField) {
   exists(StructType baseType, PromotedField child |
-    baseType = e.getBase().getType().getBaseType*().getUnderlyingType() and
+    baseType = getSelectedStructType(e) and
     (
       e.refersTo(child)
       or
@@ -65,6 +65,14 @@ private predicate implicitFieldSelection(SelectorExpr e, int i, Field implicitFi
   )
 }
 
+private class PromotedFieldSelector extends SelectorExpr {
+  PromotedFieldSelector() { this.refersTo(any(PromotedField f)) }
+}
+
+private class PromotedField extends Field {
+  PromotedField() { this = any(StructType t).getFieldOfEmbedded(_, _, _, _) }
+}
+
 /**
  * A node in the intra-procedural control-flow graph of a Go function or file.
  *