This change is the first of 3 patches to add support for specifying
the profile output from the command line via -fprofile-instr-generate=<path>,
where the specified output path/file will be overridden by the
LLVM_PROFILE_FILE environment variable.

Several changes are made to the runtime to support this:

Add a new interface __llvm_profile_override_default_filename that will
set the profile output filename, but allows LLVM_PROFILE_FILE to override.
This is the interface used by the new option.

Refactor the pid-expansion done for LLVM_PROFILE_FILE into a separate
routine that can be shared by the various filename setting routines
(so that the filename from the option can also use the "%p" syntax).

Move the truncation into setFilename, and only truncate if there is a
new filename specified (to maintain support for appending to the same
profile file in the case of multiple shared objects built with profiling).

Move the handling for a NULL filename passed to __llvm_profile_set_filename and
__llvm_profile_override_default_filename into the new setFilenamePossiblyWithPid
routine. This now correctly resets the output file to default.profraw
instead of NULL.
The handling for a null LLVM_PROFILE_FILE (which should not reset) is done
by caller setFilenameFromEnvironment.

Patch by Teresa Johnson.

llvm-svn: 236055
diff --git a/compiler-rt/lib/profile/InstrProfiling.h b/compiler-rt/lib/profile/InstrProfiling.h
index 2b1bd00..84b673c 100644
--- a/compiler-rt/lib/profile/InstrProfiling.h
+++ b/compiler-rt/lib/profile/InstrProfiling.h
@@ -62,7 +62,9 @@
  *
  * Writes to the file with the last name given to \a __llvm_profile_set_filename(),
  * or if it hasn't been called, the \c LLVM_PROFILE_FILE environment variable,
- * or if that's not set, \c "default.profdata".
+ * or if that's not set, the last name given to
+ * \a __llvm_profile_override_default_filename(), or if that's not set,
+ * \c "default.profdata".
  */
 int __llvm_profile_write_file(void);
 
@@ -77,6 +79,19 @@
  */
 void __llvm_profile_set_filename(const char *Name);
 
+/*!
+ * \brief Set the filename for writing instrumentation data, unless the
+ * \c LLVM_PROFILE_FILE environment variable was set.
+ *
+ * Unless overridden, sets the filename to be used for subsequent calls to
+ * \a __llvm_profile_write_file().
+ *
+ * \c Name is not copied, so it must remain valid.  Passing NULL resets the
+ * filename logic to the default behaviour (unless the \c LLVM_PROFILE_FILE
+ * was set in which case it has no effect).
+ */
+void __llvm_profile_override_default_filename(const char *Name);
+
 /*! \brief Register to write instrumentation data to file at exit. */
 int __llvm_profile_register_write_file_atexit(void);