[PATCH] D20454: Eliminate unnecessary file access checks in Clang driver on Windows

[Adrian McCarthy via cfe-commits]

amccarth created this revision.
amccarth added a reviewer: majnemer.
amccarth added a subscriber: cfe-commits.

This fixes the problem where the driver will look for cl.exe.exe while walking the PATH.

I looked into changing the Windows implementation of llvm::sys::fs::can_execute(), but there wasn't a satisfying way to preserve the extra checks for the callers that depend on it.  I also looked into having it actually check that the file is an executable, but this seemed to add little value at the cost of more file i/o.

http://reviews.llvm.org/D20454

Files:
  lib/Driver/MSVCToolChain.cpp

Index: lib/Driver/MSVCToolChain.cpp
===================================================================
--- lib/Driver/MSVCToolChain.cpp
+++ lib/Driver/MSVCToolChain.cpp
@@ -408,7 +408,10 @@
 
         SmallString<128> FilePath(PathSegment);
         llvm::sys::path::append(FilePath, "cl.exe");
-        if (llvm::sys::fs::can_execute(FilePath.c_str()) &&
+        // Checking if cl.exe exists is a small optimization over calling
+        // can_execute, which really only checks for existence but will also do
+        // extra checks for cl.exe.exe.  These add up when walking a long path.
+        if (llvm::sys::fs::exists(FilePath.c_str()) &&
             !llvm::sys::fs::equivalent(FilePath.c_str(), clangProgramPath)) {
           // If we found it on the PATH, use it exactly as is with no
           // modifications.


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