ScanDirForExecutable on Windows fails to find executables with the "exe" extension in name

When the driver tries to locate a program by its name, e.g. a linker, it
scans the paths provided by the toolchain using the ScanDirForExecutable
function. If the lookup fails, the driver uses
llvm::sys::findProgramByName. Unlike llvm::sys::findProgramByName,
ScanDirForExecutable is not aware of file extensions. If the program has
the "exe" extension in its name, which is very common on Windows,
ScanDirForExecutable won't find it under the toolchain-provided paths.

This patch changes the Windows version of the "`can_execute`" function
called by ScanDirForExecutable to respect file extensions, similarly to
llvm::sys::findProgramByName.

Patch by Oleg Ranevskyy

Reviewers: rnk

Differential Revision: http://reviews.llvm.org/D12711

llvm-svn: 247358

llvm/include/llvm/Support/FileSystem.h

@@ -378,9 +378,7 @@ inline bool exists(const Twine &Path) {
 ///
 /// @param Path Input path.
 /// @returns True if we can execute it, false otherwise.
-inline bool can_execute(const Twine &Path) {
-  return !access(Path, AccessMode::Execute);
-}
+bool can_execute(const Twine &Path);
 
 /// @brief Can we write this file?
 ///

llvm/lib/Support/Unix/Path.inc

@@ -325,6 +325,10 @@ std::error_code access(const Twine &Path, AccessMode Mode) {
   return std::error_code();
 }
 
+bool can_execute(const Twine &Path) {
+  return !access(Path, AccessMode::Execute);
+}
+
 bool equivalent(file_status A, file_status B) {
   assert(status_known(A) && status_known(B));
   return A.fs_st_dev == B.fs_st_dev &&

llvm/lib/Support/Windows/Path.inc

@@ -302,6 +302,11 @@ std::error_code access(const Twine &Path, AccessMode Mode) {
   return std::error_code();
 }
 
+bool can_execute(const Twine &Path) {
+  return !access(Path, AccessMode::Execute) ||
+         !access(Path + ".exe", AccessMode::Execute);
+}
+
 bool equivalent(file_status A, file_status B) {
   assert(status_known(A) && status_known(B));
   return A.FileIndexHigh      == B.FileIndexHigh &&