diff --git a/llvm/test/lit.cfg b/llvm/test/lit.cfg
index ac8d4497f09110ec3002dfe4a754195263406126..ec5b52ef47dc4188a766ded8b1e938fcc236e08a 100644
--- a/llvm/test/lit.cfg
+++ b/llvm/test/lit.cfg
@@ -202,20 +202,17 @@ config.substitutions.append( ('%exeext', config.llvm_exe_ext) )
 # tools that might happen to be in the user's PATH.  Thus this list
 # includes every tool placed in $(LLVM_OBJ_ROOT)/$(BuildMode)/bin
 # (llvm_tools_dir in lit parlance).
-                # Don't match 'bugpoint-' or 'clang-'.
-                # Don't match '/clang' or '-clang'.
-if os.pathsep == ';':
-    pathext = os.environ.get('PATHEXT', '').split(';')
-else:
-    pathext = ['']
-# Regex to reject matching a hyphen
-NOHYPHEN = r"(?<!-)"
+
+# Avoid matching RUN line fragments that are actually part of
+# path names or options or whatever.
+# The regex is a pre-assertion to avoid matching a preceding
+# dot, hyphen, carat, or slash (.foo, -foo, etc.).  Some patterns
+# also have a post-assertion to not match a trailing hyphen (foo-).
+NOJUNK = r"(?<!\.|-|\^|/)"
 
 for pattern in [r"\bbugpoint\b(?!-)",
-                r"(?<!/|-)\bclang\b(?!-)",
-                r"\bgold\b",
-                # Match llc but not -llc
-                NOHYPHEN + r"\bllc\b",
+                NOJUNK + r"\bclang\b(?!-)",
+                NOJUNK + r"\bllc\b",
                 r"\blli\b",
                 r"\bllvm-PerfectShuffle\b",
                 r"\bllvm-ar\b",
@@ -227,7 +224,6 @@ for pattern in [r"\bbugpoint\b(?!-)",
                 r"\bllvm-dis\b",
                 r"\bllvm-dwarfdump\b",
                 r"\bllvm-extract\b",
-                r"\bllvm-jistlistener\b",
                 r"\bllvm-link\b",
                 r"\bllvm-lto\b",
                 r"\bllvm-mc\b",
@@ -238,17 +234,11 @@ for pattern in [r"\bbugpoint\b(?!-)",
                 r"\bllvm-ranlib\b",
                 r"\bllvm-readobj\b",
                 r"\bllvm-rtdyld\b",
-                r"\bllvm-shlib\b",
                 r"\bllvm-size\b",
                 r"\bllvm-tblgen\b",
                 r"\bllvm-c-test\b",
-                # Match llvmc but not -llvmc
-                NOHYPHEN + r"\bllvmc\b",
-                # Match lto but not -lto
-                NOHYPHEN + r"\blto\b",
                 r"\bmacho-dump\b",
-                # Don't match '.opt', '-opt', '^opt' or '/opt'.
-                r"(?<!\.|-|\^|/)\bopt\b",
+                NOJUNK + r"\bopt\b",
                 r"\bFileCheck\b",
                 r"\bFileUpdate\b",
                 r"\bc-index-test\b",
@@ -263,15 +253,16 @@ for pattern in [r"\bbugpoint\b(?!-)",
     # name being surrounded by \b word match operators.  If the
     # pattern starts with "| ", include it in the string to be
     # substituted.
-    substitution = re.sub(r"^(\\)?((\| )?)\W+b([0-9A-Za-z-_]+)\\b\W*$",
-                          r"\2" + llvm_tools_dir + "/" + r"\4",
+    tool_match = re.match(r"^(\\)?((\| )?)\W+b([0-9A-Za-z-_]+)\\b\W*$",
                           pattern)
-    for ext in pathext:
-        substitution_ext = substitution + ext
-        if os.path.exists(substitution_ext):
-             substitution = substitution_ext
-             break
-    config.substitutions.append((pattern, substitution))
+    tool_pipe = tool_match.group(2)
+    tool_name = tool_match.group(4)
+    tool_path = lit.util.which(tool_name, llvm_tools_dir)
+    if not tool_path:
+        # Warn, but still provide a substitution.
+        lit_config.note('Did not find ' + tool_name + ' in ' + llvm_tools_dir)
+        tool_path = llvm_tools_dir + '/' + tool_name
+    config.substitutions.append((pattern, tool_pipe + tool_path))
 
 ### Features