Add support for Bazel builds on Windows with `clang-cl`.

[chandlerc]

Summary

Adds basic --config=clang-cl to set up the basic options needed, and
then fix a number of issues that surface in Windows builds for me.

With these fixes, //llvm/... builds cleanly. One unittest still fails,
but its just due to running out of stack space due to creating a large
number of short-lived stack variables. The test should probably be
decomposed into a set of tests (LegalizerInfoTest::RuleSets), but that
seemed like too invasive of a change here and with everything building
cleanly this isn't disrupting me experimenting with Windows builds.

[chandlerc]

Add at least one obvious fix needed in Clang's build rules as well.

[GMNGeoffrey]

utils/bazel/llvm-project-overlay/clang/BUILD.bazel

31–32

Is it actually these files that need dl? Previously we decided it was better to add it the root library that used it. We're already setting it in llvm:Support, which this depends on, so I don't think this should be necessary (https://github.com/llvm/llvm-project/blob/0eed292fbae22a8856682b07e1cb968424b49941/utils/bazel/llvm-project-overlay/llvm/BUILD.bazel#L211)

utils/bazel/llvm-project-overlay/llvm/unittests/BUILD.bazel

115

Hmmm unfortunate that these have to increase specifically for windows. Do windows tests take longer overall? We could change the actual timeouts corresponding to the timeout names instead.

[chandlerc]

Update based on review...

[chandlerc]

Updated, PTAL

utils/bazel/llvm-project-overlay/llvm/unittests/BUILD.bazel

115

Tests aren't generally slower, just certain *kinds* of tests. =/

Specifically, GoogleTest's "death tests" are both much slower and have much higher variability on Windows AFAICT.

I can defer these if you want and try to get statistics on how important they are, and where. I just added these when during testing I got some timeouts.

[GMNGeoffrey]

utils/bazel/llvm-project-overlay/llvm/unittests/BUILD.bazel

115

Bleh. Seems like no good solution. This is fine.

utils/bazel/.bazelrc

 build:generic_gcc --cxxopt=-Wno-class-memaccess --host_cxxopt=-Wno-class-memaccess
 build:generic_gcc --copt=-Wno-maybe-uninitialized --host_copt=-Wno-maybe-uninitialized
 build:generic_gcc --copt=-Wno-misleading-indentation --host_copt=-Wno-misleading-indentation
 
 # Use `-Werror` for GCC to make sure warnings don't slip past.
 build:generic_gcc --copt=-Werror --host_copt=-Werror
 
 ###############################################################################
-# Windows specific flags for building with VC.
+# Generic Windows flags common to both MSVC and Clang.
 ###############################################################################
 
+# Yay for security warnings. Boo for non-standard.
+build:windows --copt=/D_CRT_SECURE_NO_WARNINGS --host_copt=/D_CRT_SECURE_NO_WARNINGS
+
+###############################################################################
+# Windows specific flags for building with MSVC.
+###############################################################################
+
+build:msvc --config=windows
+
 build:msvc --copt=/WX --host_copt=/WX    # Treat warnings as errors...
 # ...but disable the ones that are violated
 build:msvc --copt=/wd4141 --host_copt=/wd4141 # inline used more than once
 build:msvc --copt=/wd4244 --host_copt=/wd4244 # conversion type -> type
 build:msvc --copt=/wd4267 --host_copt=/wd4267 # conversion size_t -> type
 build:msvc --copt=/wd4273 --host_copt=/wd4273 # multiple definitions with different dllimport
 build:msvc --copt=/wd4319 --host_copt=/wd4319 # zero-extending after complement
 build:msvc --copt=/wd4624 --host_copt=/wd4624 # destructor was implicitly defined as deleted
 build:msvc --copt=/wd4804 --host_copt=/wd4804 # comparisons between bool and int
 build:msvc --copt=/wd4805 --host_copt=/wd4805 # comparisons between bool and int
 
 build:msvc --linkopt=/WX --host_linkopt=/WX # Treat warnings as errors...
 # ...but disable the ones that are violated.
 build:msvc --linkopt=/IGNORE:4001 --host_linkopt=/IGNORE:4001 # no object files
 
-# Yay for security warnings. Boo for non-standard.
-build:msvc --copt=/D_CRT_SECURE_NO_WARNINGS --host_copt=/D_CRT_SECURE_NO_WARNINGS
+###############################################################################
+# Options for Windows `clang-cl` builds.
+###############################################################################
+
+# We just start with the baseline Windows config as `clang-cl` doesn't accept
+# some of the generic Clang flags.
+build:clang-cl --config=windows
+
+# Switch from MSVC to the `clang-cl` compiler.
+build:clang-cl --compiler=clang-cl
+
+# C++14 standard version is required.
+build:clang-cl --cxxopt=/std:c++14 --host_cxxopt=/std:c++14
+
+# Use Clang's internal warning flags instead of the ones that sometimes map
+# through to MSVC's flags.
+build:clang-cl --copt=/clang:-Wall --host_copt=/clang:-Wall
+build:clang-cl --copt=/clang:-Werror --host_copt=/clang:-Werror
+
+# This doesn't appear to be enforced by any upstream bot.
+build:clang-cl --copt=/clang:-Wno-unused --host_copt=/clang:-Wno-unused
+
+# There appears to be an unused constant in GoogleTest on Windows.
+build:clang-cl --copt=/clang:-Wno-unused-const-variable --host_copt=/clang:-Wno-unused-const-variable
 
 ###############################################################################
 
 ###############################################################################
 # Configuration for building remotely using Remote Build Execution (RBE)
 # Based on https://github.com/bazelbuild/bazel-toolchains/blob/master/bazelrc/bazel-1.0.0.bazelrc
 ###############################################################################
 

utils/bazel/llvm-project-overlay/clang/BUILD.bazel

 cc_binary(
     name = "clang-tblgen",
     srcs = glob([
         "utils/TableGen/*.cpp",
         "utils/TableGen/*.h",
     ]),
     copts = [
         "$(STACK_FRAME_UNLIMITED)",
     ],
-    linkopts = ["-ldl"],
     stamp = 0,
     deps = [
         "//llvm:Support",
         "//llvm:TableGen",
         "//llvm:config",
     ],
 )
 
 gentbl(

utils/bazel/llvm-project-overlay/llvm/BUILD.bazel

deps = [
         ":Support",
     ],
 )
 
 cc_binary(
     name = "llvm-mca",
     srcs = glob([
         "tools/llvm-mca/*.cpp",
+        "tools/llvm-mca/*.h",
         "tools/llvm-mca/Views/*.cpp",
+        "tools/llvm-mca/Views/*.h",
     ]),
     copts = llvm_copts,
     stamp = 0,
     deps = [
         ":AllTargetsAsmParsers",
         ":AllTargetsCodeGens",
         ":AllTargetsDisassemblers",
         ":AllTargetsMCAs",

utils/bazel/llvm-project-overlay/llvm/config.bzl

 
 posix_defines = [
     "LLVM_ON_UNIX=1",
     "HAVE_BACKTRACE=1",
     "BACKTRACE_HEADER=<execinfo.h>",
     r'LTDL_SHLIB_EXT=\".so\"',
     r'LLVM_PLUGIN_EXT=\".so\"',
     "LLVM_ENABLE_THREADS=1",
-    "HAVE_SYSEXITS_H=1",
-    "HAVE_UNISTD_H=1",
-    "HAVE_STRERROR_R=1",
+    "HAVE_DEREGISTER_FRAME=1",
     "HAVE_LIBPTHREAD=1",
     "HAVE_PTHREAD_GETNAME_NP=1",
-    "HAVE_PTHREAD_SETNAME_NP=1",
     "HAVE_PTHREAD_GETSPECIFIC=1",
+    "HAVE_PTHREAD_H=1",
+    "HAVE_PTHREAD_SETNAME_NP=1",
     "HAVE_REGISTER_FRAME=1",
-    "HAVE_DEREGISTER_FRAME=1",
+    "HAVE_SETENV_R=1",
+    "HAVE_STRERROR_R=1",
+    "HAVE_SYSEXITS_H=1",
+    "HAVE_UNISTD_H=1",
 ]
 
 linux_defines = posix_defines + [
     "_GNU_SOURCE",
     "HAVE_LINK_H=1",
     "HAVE_LSEEK64=1",
     "HAVE_MALLINFO=1",
     "HAVE_POSIX_FALLOCATE=1",

utils/bazel/llvm-project-overlay/llvm/include/llvm/Config/config.h

 
 /* Define to 1 if you have the `pread' function. */
 #define HAVE_PREAD 1
 
 /* Have pthread_getspecific */
 #define HAVE_PTHREAD_GETSPECIFIC 1
 
 /* Define to 1 if you have the <pthread.h> header file. */
-#define HAVE_PTHREAD_H 1
+/* HAVE_PTHREAD_H defined in Bazel */
 
 /* Have pthread_mutex_lock */
 #define HAVE_PTHREAD_MUTEX_LOCK 1
 
 /* Have pthread_rwlock_init */
 #define HAVE_PTHREAD_RWLOCK_INIT 1
 
 /* Define to 1 if you have the `sbrk' function. */
 /* HAVE_SBRK defined in Bazel */
 
 /* Define to 1 if you have the `setenv' function. */
-#define HAVE_SETENV 1
+/* HAVE_SETENV defined in Bazel */
 
 /* Define to 1 if you have the `setrlimit' function. */
 #define HAVE_SETRLIMIT 1
 
 /* Define to 1 if you have the `sigaltstack' function. */
 #define HAVE_SIGALTSTACK 1
 
 /* Define to 1 if you have the <signal.h> header file. */

utils/bazel/llvm-project-overlay/llvm/unittests/BUILD.bazel

cc_library(
     textual_hdrs = glob(
         ["CodeGen/*.inc"],
         allow_empty = False,
     ),
 )
 
 cc_test(
     name = "codegen_tests",
-    size = "small",
+    size = "medium",
     srcs = glob(
         [
             "CodeGen/*.cpp",
             "CodeGen/*.h",
         ],
         allow_empty = False,
     ),
     deps = [
deps = [
         "//llvm:Target",
         "//llvm:gtest",
         "//llvm:gtest_main",
     ],
 )
 
 cc_test(
     name = "debuginfo_tests",
-    size = "small",
+    size = "medium",
     srcs = glob(
         [
             "DebugInfo/DWARF/*.cpp",
             "DebugInfo/DWARF/*.h",
             # TODO: Re-enable these when they stop crashing.
             #"DebugInfo/PDB/*.cpp",
             #"DebugInfo/PDB/*.h",
         ],
deps = [
         "//llvm:Support",
         "//llvm:gtest",
         "//llvm:gtest_main",
     ],
 )
 
 cc_test(
     name = "execution_engine_mcjit_tests",
-    size = "small",
+    size = "medium",
     srcs = glob(
         [
             "ExecutionEngine/MCJIT/*.cpp",
             "ExecutionEngine/MCJIT/*.h",
         ],
         allow_empty = False,
     ),
     copts = [
deps = [
         "//llvm:Support",
         "//llvm:gtest",
         "//llvm:gtest_main",
     ],
 )
 
 cc_test(
     name = "execution_engine_orc_tests",
-    size = "small",
+    size = "medium",
     srcs = glob(
         [
             "ExecutionEngine/Orc/*.cpp",
             "ExecutionEngine/Orc/*.h",
         ],
         allow_empty = False,
     ),
     args = ["--gtest_filter=-ObjectLinkingLayerTest.TestSetProcessAllSections"],
deps = [
         "//llvm:Support",
         "//llvm:gtest",
         "//llvm:gtest_main",
     ],
 )
 
 cc_test(
     name = "mi_tests",
-    size = "small",
+    size = "medium",
     srcs = glob(
         ["MI/*.cpp"],
         allow_empty = False,
     ),
     deps = [
         "//llvm:AllTargetsAsmParsers",
         "//llvm:AllTargetsCodeGens",
         "//llvm:CodeGen",
deps = [
         "//llvm:ProfileData",
         "//llvm:Support",
         "//llvm:TestingSupport",
         "//llvm:gtest",
         "//llvm:gtest_main",
     ],
 )
 
+# Note that the name of this test is important as it is used in the test itself.
 cc_test(
-    name = "support_tests",
-    size = "small",
+    name = "SupportTests",
+    size = "medium",
     srcs = glob(
         [
             "Support/*.cpp",
             "Support/*.h",
         ],
         allow_empty = False,
         exclude = [
             "Support/ParallelTest.cpp",