tianshilei1992 created this revision.
Herald added a project: clang.
Herald added a subscriber: cfe-commits.
tianshilei1992 requested review of this revision.
Herald added a reviewer: jdoerfert.
Herald added a subscriber: sstefan1.
Currently, GCC toolchain can only be set via the option `--gcc-toolchain`. On
many HPC clusters, like Summit, because of its old system, the default GCC is
4.8.5. Users usually use `module load gcc/$(version)` to load another GCC.
However, the module package manager can only set some environment variables like
`PATH`, it cannot control Clang's GCC toolchain. As a result, no matter which
GCC users are using, it always ends up with the system version. What's more,
sometimes it's not easy to pass the option to the build system.
I did talk to some LLVM users about this problem. Some of them thought LLVM
works purely w/o GCC, and many thought Clang can select the right GCC they are
setting. I also saw an "issue" on GitHub about failing to compile OpenMP source
code using LLVM after a patch that set default C++ version to C++14, and it is
actually because the user compiled LLVM with GCC 6.4.0, and then set `clang` and
`clang++` as the default compiler to compile OpenMP. Since the user was using a
cluster with CentOS 7 whose default GCC is 4.8.5, and GCC 4.8.5 does not fully
support C++14, the problem occurred.
This patch added the support for setting GCC toolchain via an environment
variable `GCC_TOOLCHAIN`. It will be read if `--gcc-toolchain` is not set. In
this way, as long as those package managers set the environment variable when
loading different versions of GCC, Clang can also pick up the right version.
Repository:
rG LLVM Github Monorepo
https://reviews.llvm.org/D91107
Files:
clang/lib/Driver/ToolChains/Gnu.cpp
Index: clang/lib/Driver/ToolChains/Gnu.cpp
===================================================================
--- clang/lib/Driver/ToolChains/Gnu.cpp
+++ clang/lib/Driver/ToolChains/Gnu.cpp
@@ -1856,6 +1856,12 @@
if (A)
return A->getValue();
+ // If --gcc-toochain is not set, we then check the environment variable
+ // GCC_TOOLCHAIN because sometimes it is not easy to pass the option to the
+ // driver.
+ if (const char *GCCToolchainEnv = ::getenv("GCC_TOOLCHAIN"))
+ return GCCToolchainEnv;
+
// If we have a SysRoot, ignore GCC_INSTALL_PREFIX.
// GCC_INSTALL_PREFIX specifies the gcc installation for the default
// sysroot and is likely not valid with a different sysroot.
Index: clang/lib/Driver/ToolChains/Gnu.cpp
===================================================================
--- clang/lib/Driver/ToolChains/Gnu.cpp
+++ clang/lib/Driver/ToolChains/Gnu.cpp
@@ -1856,6 +1856,12 @@
if (A)
return A->getValue();
+ // If --gcc-toochain is not set, we then check the environment variable
+ // GCC_TOOLCHAIN because sometimes it is not easy to pass the option to the
+ // driver.
+ if (const char *GCCToolchainEnv = ::getenv("GCC_TOOLCHAIN"))
+ return GCCToolchainEnv;
+
// If we have a SysRoot, ignore GCC_INSTALL_PREFIX.
// GCC_INSTALL_PREFIX specifies the gcc installation for the default
// sysroot and is likely not valid with a different sysroot.
_______________________________________________
cfe-commits mailing list
cfe-commits@lists.llvm.org
https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
