diff --git a/llvm/utils/lit/lit/TestRunner.py b/llvm/utils/lit/lit/TestRunner.py
--- a/llvm/utils/lit/lit/TestRunner.py
+++ b/llvm/utils/lit/lit/TestRunner.py
@@ -1148,9 +1148,14 @@
     return re.compile(r)
 
 def applySubstitutions(script, substitutions):
-    """Apply substitutions to the script.  Allow full regular expression syntax.
+    """
+    Apply substitutions to the script.  Allow full regular expression syntax.
     Replace each matching occurrence of regular expression pattern a with
-    substitution b in line ln."""
+    substitution b in line ln.
+
+    If a substitution expands into another substitution, it is expanded
+    recursively until the line has no more expandable substitutions.
+    """
     def processLine(ln):
         # Apply substitutions
         for a,b in substitutions:
@@ -1167,9 +1172,17 @@
 
         # Strip the trailing newline and any extra whitespace.
         return ln.strip()
+
+    def fullyProcessLine(ln):
+        processed = processLine(ln)
+        while processed != ln:
+            ln = processed
+            processed = processLine(ln)
+        return processed
+
     # Note Python 3 map() gives an iterator rather than a list so explicitly
     # convert to list before returning.
-    return list(map(processLine, script))
+    return list(map(fullyProcessLine, script))
 
 
 class ParserKind(object):