Use LLD when building with downloaded GPU toolchain
This improves build times when using the downloaded clang toolchain.
Additionally, remove '-B/usr/bin' flags from the cuda CROSSTOOL when using
the downloaded toolchain.
It was forcing 'clang' to first search for the linker in '/usr/bin',
preventing downloaded LLD from being selected.
PiperOrigin-RevId: 211430374
diff --git a/configure.py b/configure.py
index 7edab53..361bd47 100644
--- a/configure.py
+++ b/configure.py
@@ -1543,6 +1543,10 @@
if environ_cp.get('TF_DOWNLOAD_CLANG') != '1':
# Set up which clang we should use as the cuda / host compiler.
set_clang_cuda_compiler_path(environ_cp)
+ else:
+ # Use downloaded LLD for linking.
+ write_to_bazelrc('build:cuda_clang --config=download_clang_use_lld')
+ write_to_bazelrc('test:cuda_clang --config=download_clang_use_lld')
else:
# Set up which gcc nvcc should use as the host compiler
# No need to set this on Windows
diff --git a/third_party/gpus/crosstool/CROSSTOOL.tpl b/third_party/gpus/crosstool/CROSSTOOL.tpl
index 3972c96..3189cf8 100644
--- a/third_party/gpus/crosstool/CROSSTOOL.tpl
+++ b/third_party/gpus/crosstool/CROSSTOOL.tpl
@@ -208,7 +208,7 @@
action: "c++-link-dynamic-library"
action: "c++-link-nodeps-dynamic-library"
flag_group {
- flag: "-B/usr/bin/"
+ %{linker_bin_path_flag}
}
}
}
@@ -446,7 +446,7 @@
action: "c++-link-dynamic-library"
action: "c++-link-nodeps-dynamic-library"
flag_group {
- flag: "-B/usr/bin/"
+ %{linker_bin_path_flag}
}
}
}
diff --git a/third_party/gpus/cuda_configure.bzl b/third_party/gpus/cuda_configure.bzl
index f6a39ae..5648b15 100644
--- a/third_party/gpus/cuda_configure.bzl
+++ b/third_party/gpus/cuda_configure.bzl
@@ -1303,6 +1303,19 @@
host_compiler_includes = _host_compiler_includes(repository_ctx, cc_fullpath)
cuda_defines = {}
+ # Bazel sets '-B/usr/bin' flag to workaround build errors on RHEL (see
+ # https://github.com/bazelbuild/bazel/issues/760).
+ # However, this stops our custom clang toolchain from picking the provided
+ # LLD linker, so we're only adding '-B/usr/bin' when using non-downloaded
+ # toolchain.
+ # TODO: when bazel stops adding '-B/usr/bin' by default, remove this
+ # flag from the CROSSTOOL completely (see
+ # https://github.com/bazelbuild/bazel/issues/5634)
+ if should_download_clang:
+ cuda_defines["%{linker_bin_path_flag}"] = ""
+ else:
+ cuda_defines["%{linker_bin_path_flag}"] = 'flag: "-B/usr/bin"'
+
if is_cuda_clang:
cuda_defines["%{host_compiler_path}"] = str(cc)
cuda_defines["%{host_compiler_warnings}"] = """
diff --git a/tools/bazel.rc b/tools/bazel.rc
index 660e3d3..601e07f 100644
--- a/tools/bazel.rc
+++ b/tools/bazel.rc
@@ -33,6 +33,11 @@
build:download_clang --crosstool_top=@local_config_download_clang//:toolchain
build:download_clang --define=using_clang=true
+# Instruct clang to use LLD for linking.
+# This only works with GPU builds currently, since Bazel sets -B/usr/bin in
+# auto-generated CPU crosstool, forcing /usr/bin/ld.lld to be preferred over
+# the downloaded one.
+build:download_clang_use_lld --linkopt='-fuse-ld=lld'
build:cuda --crosstool_top=@local_config_cuda//crosstool:toolchain
build:cuda --define=using_cuda=true --define=using_cuda_nvcc=true