[docs] add Windows examples to ThinLTO.rst

Reviewers: pcc, ruiu

Reviewed By: ruiu

Subscribers: mehdi_amini, eraman, cfe-commits

Differential Revision: https://reviews.llvm.org/D37943

llvm-svn: 313425

clang/docs/ThinLTO.rst

@@ -63,7 +63,7 @@ ThinLTO is currently supported for the following linkers:
 - **ld64**:
   Starting with `Xcode 8 <https://developer.apple.com/xcode/>`_.
 - **lld**:
-  Starting with r284050 (ELF only).
+  Starting with r284050 for ELF, r298942 for COFF.
 
 Usage
 =====
@@ -78,6 +78,13 @@ To utilize ThinLTO, simply add the -flto=thin option to compile and link. E.g.
   % clang -flto=thin -O2 file1.c file2.c -c
   % clang -flto=thin -O2 file1.o file2.o -o a.out
 
+When using lld-link, the -flto option need only be added to the compile step:
+
+.. code-block:: console
+
+  % clang-cl -flto=thin -O2 -c file1.c file2.c
+  % lld-link /out:a.exe file1.obj file2.obj
+
 As mentioned earlier, by default the linkers will launch the ThinLTO backend
 threads in parallel, passing the resulting native object files back to the
 linker for the final native link.  As such, the usage model the same as
@@ -111,6 +118,8 @@ be reduced to ``N`` via:
   ``-Wl,-mllvm,-threads=N``
 - lld:
   ``-Wl,--thinlto-jobs=N``
+- lld-link:
+  ``/opt:lldltojobs=N``
 
 Incremental
 -----------
@@ -125,7 +134,7 @@ which currently must be enabled through a linker option.
   ``-Wl,-cache_path_lto,/path/to/cache``
 - ELF lld (as of LLVM 5.0):
   ``-Wl,--thinlto-cache-dir=/path/to/cache``
-- COFF lld (as of LLVM 6.0):
+- COFF lld-link (as of LLVM 6.0):
   ``/lldltocache:/path/to/cache``
 
 Cache Pruning
@@ -138,7 +147,7 @@ policy string. The cache policy must be specified with a linker option.
 
 - ELF lld (as of LLVM 5.0):
   ``-Wl,--thinlto-cache-policy,POLICY``
-- COFF lld (as of LLVM 6.0):
+- COFF lld-link (as of LLVM 6.0):
   ``/lldltocachepolicy:POLICY``
 
 A policy string is a series of key-value pairs separated by ``:`` characters.
@@ -187,13 +196,20 @@ To bootstrap clang/LLVM with ThinLTO, follow these steps:
    when configuring the bootstrap compiler build:
 
   * ``-DLLVM_ENABLE_LTO=Thin``
-  * ``-DLLVM_PARALLEL_LINK_JOBS=1``
-    (since the ThinLTO link invokes parallel backend jobs)
   * ``-DCMAKE_C_COMPILER=/path/to/host/clang``
   * ``-DCMAKE_CXX_COMPILER=/path/to/host/clang++``
   * ``-DCMAKE_RANLIB=/path/to/host/llvm-ranlib``
   * ``-DCMAKE_AR=/path/to/host/llvm-ar``
 
+  Or, on Windows:
+
+  * ``-DLLVM_ENABLE_LTO=Thin``
+  * ``-DCMAKE_C_COMPILER=/path/to/host/clang-cl.exe``
+  * ``-DCMAKE_CXX_COMPILER=/path/to/host/clang-cl.exe``
+  * ``-DCMAKE_LINKER=/path/to/host/lld-link.exe``
+  * ``-DCMAKE_RANLIB=/path/to/host/llvm-ranlib.exe``
+  * ``-DCMAKE_AR=/path/to/host/llvm-ar.exe``
+
 #. To use additional linker arguments for controlling the backend
    parallelism_ or enabling incremental_ builds of the bootstrap compiler,
    after configuring the build, modify the resulting CMakeCache.txt file in the