用Bazel构建LLVM
我有一个正在使用CMake的项目，我想把它切换到Bazel。主要依赖项是LLVM，我使用它生成LLVM IR。环顾四周，似乎没有很多关于这方面的指导，因为只有TensorFlow似乎使用Bazel的LLVM (据我所知，自动生成它的配置)。我还发现了一个关于bazel的文章-讨论，它讨论了一个类似的问题，尽管我复制它的尝试失败了。
目前，我最好的运行方式必须是这个(fetcher.bzl)：
def _impl(ctx):
# Download LLVM master
ctx.download_and_extract(url = "https://github.com/llvm-mirror/llvm/archive/master.zip")
# Run `cmake llvm-master` to generate configuration.
ctx.execute(["cmake", "llvm-master"])
# The bazel-discuss thread says to delete llvm-master, but I've
# found that only generated files are pulled out of master, so all
# the non-generated ones get dropped if I delete this.
# ctx.execute(["rm", "-r", "llvm-master"])
# Generate a BUILD file for the LLVM dependency.
ctx.file('BUILD', """
# Build a library with all the LLVM code in it.
cc_library(
name = "lib",
srcs = glob(["**/*.cpp"]),
hdrs = glob(["**/*.h"]),
# Include the x86 target and all include files.
# Add those under llvm-master/... as well because only built files
# seem to appear under include/...
copts = [
"-Ilib/Target/X86",
"-Iinclude",
"-Illvm-master/lib/Target/X86",
"-Illvm-master/include",
],
# Include here as well, not sure whether this or copts is
# actually doing the work.
includes = [
"include",
"llvm-master/include",
],
visibility = ["//visibility:public"],
# Currently picking up some gtest targets, I have that dependency
# already, so just link it here until I filter those out.
deps = [
"@gtest//:gtest_main",
],
)
""")
# Generate an empty workspace file
ctx.file('WORKSPACE', '')
get_llvm = repository_rule(implementation = _impl)然后，我的WORKSPACE文件如下所示：
load(":fetcher.bzl", "get_llvm")
git_repository(
name = "gflags",
commit = "46f73f88b18aee341538c0dfc22b1710a6abedef", # 2.2.1
remote = "https://github.com/gflags/gflags.git",
)
new_http_archive(
name = "gtest",
url = "https://github.com/google/googletest/archive/release-1.8.0.zip",
sha256 = "f3ed3b58511efd272eb074a3a6d6fb79d7c2e6a0e374323d1e6bcbcc1ef141bf",
build_file = "gtest.BUILD",
strip_prefix = "googletest-release-1.8.0",
)
get_llvm(name = "llvm")然后，我将使用bazel build @llvm//:lib --verbose_failures运行这个程序。
我会不断地从丢失的头文件中得到错误。最后，我发现运行cmake llvm-master会将许多头文件生成到当前目录中，但似乎将非生成的头文件保留在llvm-master/中。我在llvm-master/下添加了相同的包含目录，这似乎捕获了很多文件。但是，目前看来tblgen没有运行，而且我仍然缺少编译所需的关键头。我目前的错误是：
In file included from external/llvm/llvm-master/include/llvm/CodeGen/MachineOperand.h:18:0,
from external/llvm/llvm-master/include/llvm/CodeGen/MachineInstr.h:24,
from external/llvm/llvm-master/include/llvm/CodeGen/MachineBasicBlock.h:22,
from external/llvm/llvm-master/include/llvm/CodeGen/GlobalISel/MachineIRBuilder.h:20,
from external/llvm/llvm-master/include/llvm/CodeGen/GlobalISel/ConstantFoldingMIRBuilder.h:13,
from external/llvm/llvm-master/unittests/CodeGen/GlobalISel/PatternMatchTest.cpp:10:
external/llvm/llvm-master/include/llvm/IR/Intrinsics.h:42:38: fatal error: llvm/IR/IntrinsicEnums.inc: No such file or directory特别是试图查找这个文件时，我没有看到任何IntrinsicEnums.inc、IntrinsicEnums.h或IntrinsicEnums.dt。我确实看到了很多Instrinsics*.td，所以也许其中一个会生成这个特定的文件？
似乎tblgen应该将*.td文件转换为*.h和*.cpp文件(如果我误解了，请纠正我)。然而，这似乎没有运行。我看到在Tensorflow的项目中，他们有一个gentbl()构建宏，尽管对我来说复制它是不实际的，因为它对Tensorflow的其他构建基础设施有太多的依赖。
在没有像Tensorflow这样庞大而复杂的系统的情况下，有没有办法做到这一点？
回答 1
Stack Overflow用户
发布于 2018-10-14 22:34:57
我在llvm dev邮件列表这里上发布了一些有趣的回复。LLVM显然不是为了支持Bazel而设计的，而且做得并不特别好。从理论上讲，通过使用Ninja输出所有编译命令，然后从Bazel中使用它们，这似乎是可能的。这可能非常困难，需要一个单独的工具来输出Skylark代码，由Bazel运行。
对于我正在进行的项目规模来说，这似乎相当复杂，所以我的解决办法是从releases.llvm.org下载预构建的二进制文件。这包括所有必要的头、库和工具二进制文件。我用Bazel语言为我的自定义编程语言制作了一个简单但功能强大的工具链。
简单示例(有限但重点突出)：https://github.com/dgp1130/llvm-bazel-foolang
完整示例(更复杂、更不集中)：https://github.com/dgp1130/sanity-lang
https://stackoverflow.com/questions/51585688
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