Add profiling support, through the rustc -Z profile flag.

When -Z profile is passed, the GCDAProfiling LLVM pass is added
to the pipeline, which uses debug information to instrument the IR.
After compiling with -Z profile, the $(OUT_DIR)/$(CRATE_NAME).gcno
file is created, containing initial profiling information.
After running the program built, the $(OUT_DIR)/$(CRATE_NAME).gcda
file is created, containing branch counters.

The created *.gcno and *.gcda files can be processed using
the "llvm-cov gcov" and "lcov" tools. The profiling data LLVM
generates does not faithfully follow the GCC's format for *.gcno
and *.gcda files, and so it will probably not work with other tools
(such as gcov itself) that consume these files.

1 files changed, 3 insertions, 0 deletions

diff --git a/src/bootstrap/config.toml.example b/src/bootstrap/config.toml.example
index 0309eca0e5d..93997027dbb 100644
--- a/src/bootstrap/config.toml.example
+++ b/src/bootstrap/config.toml.example
@@ -147,6 +147,9 @@
 # Build the sanitizer runtimes
 #sanitizers = false
 
+# Build the profiler runtime
+#profiler = false
+
 # Indicates whether the OpenSSL linked into Cargo will be statically linked or
 # not. If static linkage is specified then the build system will download a
 # known-good version of OpenSSL, compile it, and link it to Cargo.