[ThinLTO] Correct documentation on default number of threads

Summary:
The number of threads used for ThinLTO backend parallelism was
dropped to the number of cores in r284618 to avoid oversubscribing
physical cores due to hyperthreading. This updates the documentation
to reflect that change.

Fixes PR38610.

Reviewers: pcc

Subscribers: mehdi_amini, inglorion, eraman, steven_wu, dexonsmith, cfe-commits

Differential Revision: https://reviews.llvm.org/D50882

llvm-svn: 340021

diff --git a/clang/docs/ThinLTO.rst b/clang/docs/ThinLTO.rst
index 38873f464c29ca637d41e3ec45d3f43316abadd5..05a0b67dbab9c13010ee2aec63ffcd788b347308 100644 (file)
--- a/clang/docs/ThinLTO.rst
+++ b/clang/docs/ThinLTO.rst
@@ -105,7 +105,9 @@ Controlling Backend Parallelism
 -------------------------------
 .. _parallelism:
 
-By default, the ThinLTO link step will launch up to
+By default, the ThinLTO link step will launch as many
+threads in parallel as there are cores. If the number of
+cores can't be computed for the architecture, then it will launch
 ``std::thread::hardware_concurrency`` number of threads in parallel.
 For machines with hyper-threading, this is the total number of
 virtual cores. For some applications and machine configurations this