clang build script: If doing bootstrap builds, use lld as linker for later stages on win and linux.

Now that we do PGO, linux already used lld in pgo builds, so this
doesn't really change much on linux (lld is now used for building
the instrumented compiler too, which isn't that big a change).

No intended behavior change.

Bug: 958852
Change-Id: Ia19d47fd5d3e366b513570041e3b3a16d05a8b93
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1636672Reviewed-by: Hans Wennborg <hans@chromium.org>
Commit-Queue: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#671535}

tools/clang/scripts/build.py

@@ -370,7 +370,12 @@ def main():
   if args.skip_build:
     return 0
 
-  cc, cxx = None, None
+  # The variable "lld" is only used on Windows because only there does setting
+  # CMAKE_LINKER have an effect: On Windows, the linker is called directly,
+  # while elsewhere it's called through the compiler driver, and we pass
+  # -fuse-ld=lld there to make the compiler driver call the linker (by setting
+  # LLVM_ENABLE_LLD).
+  cc, cxx, lld = None, None, None
 
   cflags = []
   cxxflags = []
@@ -430,9 +435,7 @@ def main():
     if args.pgo:
       # Need libclang_rt.profile
       projects += ';compiler-rt'
-    if (sys.platform.startswith('linux') and args.pgo) or args.lto_lld:
-      # Old gnu ld doesn't handle libclang_rt.profile well.
-      # TODO(crbug.com/958852): Always use lld for later stages.
+    if sys.platform != 'darwin' or args.lto_lld:
       projects += ';lld'
     if sys.platform == 'darwin':
       # Need libc++ and compiler-rt for the bootstrap compiler on mac.
@@ -469,6 +472,7 @@ def main():
           ])
     if cc is not None:  bootstrap_args.append('-DCMAKE_C_COMPILER=' + cc)
     if cxx is not None: bootstrap_args.append('-DCMAKE_CXX_COMPILER=' + cxx)
+    if lld is not None: bootstrap_args.append('-DCMAKE_LINKER=' + lld)
     RunCommand(['cmake'] + bootstrap_args + [os.path.join(LLVM_DIR, 'llvm')],
                msvc_arch='x64')
     RunCommand(['ninja'], msvc_arch='x64')
@@ -481,13 +485,17 @@ def main():
     if sys.platform == 'win32':
       cc = os.path.join(LLVM_BOOTSTRAP_INSTALL_DIR, 'bin', 'clang-cl.exe')
       cxx = os.path.join(LLVM_BOOTSTRAP_INSTALL_DIR, 'bin', 'clang-cl.exe')
+      lld = os.path.join(LLVM_BOOTSTRAP_INSTALL_DIR, 'bin', 'lld-link.exe')
       # CMake has a hard time with backslashes in compiler paths:
       # https://stackoverflow.com/questions/13050827
       cc = cc.replace('\\', '/')
       cxx = cxx.replace('\\', '/')
+      lld = lld.replace('\\', '/')
     else:
       cc = os.path.join(LLVM_BOOTSTRAP_INSTALL_DIR, 'bin', 'clang')
       cxx = os.path.join(LLVM_BOOTSTRAP_INSTALL_DIR, 'bin', 'clang++')
+    if sys.platform.startswith('linux'):
+      base_cmake_args.append('-DLLVM_ENABLE_LLD=ON')
 
     print('Bootstrap compiler installed.')
 
@@ -507,16 +515,13 @@ def main():
         '-DLLVM_ENABLE_PROJECTS=' + projects,
         '-DCMAKE_C_FLAGS=' + ' '.join(cflags),
         '-DCMAKE_CXX_FLAGS=' + ' '.join(cxxflags),
-        # Build with the bootstrap compiler.
-        '-DCMAKE_C_COMPILER=' + cc,
-        '-DCMAKE_CXX_COMPILER=' + cxx,
         # Build with instrumentation.
         '-DLLVM_BUILD_INSTRUMENTED=IR',
         ]
-
-    if sys.platform.startswith('linux'):
-      # Ubuntu 16's ld doesn't generate __start__ section, so link with lld.
-      instrument_args.append('-DLLVM_ENABLE_LLD=ON')
+    # Build with the bootstrap compiler.
+    if cc is not None:  instrument_args.append('-DCMAKE_C_COMPILER=' + cc)
+    if cxx is not None: instrument_args.append('-DCMAKE_CXX_COMPILER=' + cxx)
+    if lld is not None: instrument_args.append('-DCMAKE_LINKER=' + lld)
 
     RunCommand(['cmake'] + instrument_args + [os.path.join(LLVM_DIR, 'llvm')],
                msvc_arch='x64')
@@ -557,8 +562,6 @@ def main():
                                        '*.profraw')), msvc_arch='x64')
     print('Profile generated.')
 
-
-
   compiler_rt_args = [
     "-DCOMPILER_RT_BUILD_CRT=OFF",
     "-DCOMPILER_RT_BUILD_LIBFUZZER=ON",
@@ -638,6 +641,8 @@ def main():
     threads_enabled_cmake_args.append('-DCMAKE_C_COMPILER=' + cc)
   if cxx is not None:
     threads_enabled_cmake_args.append('-DCMAKE_CXX_COMPILER=' + cxx)
+  if lld is not None:
+    threads_enabled_cmake_args.append('-DCMAKE_LINKER=' + lld)
 
   if args.lto_lld:
     # Build lld with LTO. That speeds up the linker by ~10%.
@@ -653,7 +658,7 @@ def main():
         '-DCMAKE_AR=' + ar,
         '-DCMAKE_RANLIB=' + ranlib,
         '-DLLVM_ENABLE_LTO=thin',
-        '-DLLVM_USE_LINKER=lld']
+        ]
 
   RunCommand(['cmake'] + threads_enabled_cmake_args +
              [os.path.join(LLVM_DIR, 'llvm')],
@@ -666,6 +671,7 @@ def main():
   chrome_tools = list(set(default_tools + args.extra_tools))
   if cc is not None:  base_cmake_args.append('-DCMAKE_C_COMPILER=' + cc)
   if cxx is not None: base_cmake_args.append('-DCMAKE_CXX_COMPILER=' + cxx)
+  if lld is not None: base_cmake_args.append('-DCMAKE_LINKER=' + lld)
   cmake_args = base_cmake_args + compiler_rt_args + [
       '-DLLVM_ENABLE_THREADS=OFF',
       '-DCMAKE_C_FLAGS=' + ' '.join(cflags),

tools/clang/scripts/update.py

@@ -39,7 +39,7 @@ import zipfile
 # Reverting problematic clang rolls is safe, though.
 CLANG_REVISION = 'd874c057bc2361da5157553e1e2178f43c3ade1a'
 CLANG_SVN_REVISION = '363790'
-CLANG_SUB_REVISION = 2
+CLANG_SUB_REVISION = 3
 
 PACKAGE_VERSION = '%s-%s-%s' % (CLANG_SVN_REVISION, CLANG_REVISION[:8],
                                 CLANG_SUB_REVISION)