Clang build script: link against rpmalloc on Windows

This makes LLD faster, especially when performing ThinLTO.
Reduces link time of chrome.dll with 34% in official builds
with ThinLTO enabled.

It also makes regular (non-goma) builds 6% faster.

Bug: 1111798
Change-Id: I12870d5b14bf559b333260347dbb93c7e4fe8a5d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2398685
Commit-Queue: Hans Wennborg <hans@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Auto-Submit: Hans Wennborg <hans@chromium.org>
Cr-Commit-Position: refs/heads/master@{#807644}

tools/clang/scripts/build.py

@@ -290,6 +290,28 @@ def AddZlibToPath():
   return zlib_dir
 
 
+def DownloadRPMalloc():
+  """Download rpmalloc."""
+  rpmalloc_dir = os.path.join(LLVM_BUILD_TOOLS_DIR, 'rpmalloc')
+  if os.path.exists(rpmalloc_dir):
+    RmTree(rpmalloc_dir)
+
+  # Using rpmalloc bc1923f rather than the latest release (1.4.1) because
+  # it contains the fix for https://github.com/mjansson/rpmalloc/pull/186
+  # which would cause lld to deadlock.
+  # The zip file was created and uploaded as follows:
+  # $ mkdir rpmalloc
+  # $ curl -L https://github.com/mjansson/rpmalloc/archive/bc1923f436539327707b08ef9751a7a87bdd9d2f.tar.gz \
+  #     | tar -C rpmalloc --strip-components=1 -xzf -
+  # $ GZIP=-9 tar vzcf rpmalloc-bc1923f.tgz rpmalloc
+  # $ gsutil.py cp -n -a public-read rpmalloc-bc1923f.tgz \
+  #     gs://chromium-browser-clang/tools/
+  zip_name = 'rpmalloc-bc1923f.tgz'
+  DownloadAndUnpack(CDS_URL + '/tools/' + zip_name, LLVM_BUILD_TOOLS_DIR)
+  rpmalloc_dir = rpmalloc_dir.replace('\\', '/')
+  return rpmalloc_dir
+
+
 def MaybeDownloadHostGcc(args):
   """Download a modern GCC host compiler on Linux."""
   if not sys.platform.startswith('linux') or args.gcc_toolchain:
@@ -569,6 +591,10 @@ def main():
     cxxflags.append('-I' + zlib_dir)
     ldflags.append('-LIBPATH:' + zlib_dir)
 
+    # Use rpmalloc. For faster ThinLTO linking.
+    rpmalloc_dir = DownloadRPMalloc()
+    base_cmake_args.append('-DLLVM_INTEGRATED_CRT_ALLOC=' + rpmalloc_dir)
+
   if sys.platform != 'win32':
     # libxml2 is required by the Win manifest merging tool used in cross-builds.
     base_cmake_args.append('-DLLVM_ENABLE_LIBXML2=FORCE_ON')

tools/clang/scripts/update.py

@@ -39,7 +39,7 @@ import zipfile
 # Reverting problematic clang rolls is safe, though.
 # This is the output of `git describe` and is usable as a commit-ish.
 CLANG_REVISION = 'llvmorg-12-init-5627-gf086e85e'
-CLANG_SUB_REVISION = 1
+CLANG_SUB_REVISION = 2
 
 PACKAGE_VERSION = '%s-%s' % (CLANG_REVISION, CLANG_SUB_REVISION)
 RELEASE_VERSION = '12.0.0'