[clang] [Driver] Add the --gcc-triple option (PR #73214)

[Tom Stellard via cfe-commits]

https://github.com/tstellar created https://github.com/llvm/llvm-project/pull/73214

When --gcc-triple is used, the driver will search for the 'best' gcc installation that has the given triple.  This is useful for distributions that want clang to use a specific gcc triple, but do not want to pin to a specific version as would be required by using --gcc-install-dir.  Having clang linked to a specific gcc version can cause clang to stop working when the version of gcc installed on the system gets updated.

>From 72f6f3a611f237f71ce02cfb79620257a9e2d827 Mon Sep 17 00:00:00 2001
From: Tom Stellard <tstellar at redhat.com>
Date: Thu, 16 Nov 2023 05:11:04 +0000
Subject: [PATCH] [Driver] Add the --gcc-triple option

When --gcc-triple is used, the driver will search for the 'best' gcc
installation that has the given triple.  This is useful for
distributions that want clang to use a specific gcc triple, but do
not want to pin to a specific version as would be required by
using --gcc-install-dir.  Having clang linked to a specific gcc version
can cause clang to stop working when the version of gcc installed on
the system gets updated.
---
 clang/include/clang/Driver/Options.td                     | 2 ++
 clang/lib/Driver/ToolChains/Gnu.cpp                       | 8 ++++++++
 .../usr/lib/gcc/x86_64-linux-gnu/13/crtbegin.o            | 0
 .../usr/lib/gcc/x86_64-linux-gnu/13/crtend.o              | 0
 .../fedora_39_tree/usr/lib/gcc/x86_64-linux-gnu/13/crti.o | 0
 .../fedora_39_tree/usr/lib/gcc/x86_64-linux-gnu/13/crtn.o | 0
 .../usr/lib/gcc/x86_64-redhat-linux/13/crtbegin.o         | 0
 .../usr/lib/gcc/x86_64-redhat-linux/13/crtend.o           | 0
 .../usr/lib/gcc/x86_64-redhat-linux/13/crti.o             | 0
 .../usr/lib/gcc/x86_64-redhat-linux/13/crtn.o             | 0
 clang/test/Driver/gcc-prefix.cpp                          | 8 ++++++++
 11 files changed, 18 insertions(+)
 create mode 100644 clang/test/Driver/Inputs/fedora_39_tree/usr/lib/gcc/x86_64-linux-gnu/13/crtbegin.o
 create mode 100644 clang/test/Driver/Inputs/fedora_39_tree/usr/lib/gcc/x86_64-linux-gnu/13/crtend.o
 create mode 100644 clang/test/Driver/Inputs/fedora_39_tree/usr/lib/gcc/x86_64-linux-gnu/13/crti.o
 create mode 100644 clang/test/Driver/Inputs/fedora_39_tree/usr/lib/gcc/x86_64-linux-gnu/13/crtn.o
 create mode 100644 clang/test/Driver/Inputs/fedora_39_tree/usr/lib/gcc/x86_64-redhat-linux/13/crtbegin.o
 create mode 100644 clang/test/Driver/Inputs/fedora_39_tree/usr/lib/gcc/x86_64-redhat-linux/13/crtend.o
 create mode 100644 clang/test/Driver/Inputs/fedora_39_tree/usr/lib/gcc/x86_64-redhat-linux/13/crti.o
 create mode 100644 clang/test/Driver/Inputs/fedora_39_tree/usr/lib/gcc/x86_64-redhat-linux/13/crtn.o
 create mode 100644 clang/test/Driver/gcc-prefix.cpp

diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td
index b2f2bcb6ac37910..79ced47150b455d 100644
--- a/clang/include/clang/Driver/Options.td
+++ b/clang/include/clang/Driver/Options.td
@@ -773,6 +773,8 @@ def gcc_install_dir_EQ : Joined<["--"], "gcc-install-dir=">,
 def gcc_toolchain : Joined<["--"], "gcc-toolchain=">, Flags<[NoXarchOption]>,
   HelpText<"Specify a directory where Clang can find 'include' and 'lib{,32,64}/gcc{,-cross}/$triple/$version'. "
   "Clang will use the GCC installation with the largest version">;
+def gcc_triple_EQ : Joined<["--"], "gcc-triple=">,
+  HelpText<"Search for the GCC installation with the specified triple.">;
 def CC : Flag<["-"], "CC">, Visibility<[ClangOption, CC1Option]>,
   Group<Preprocessor_Group>,
     HelpText<"Include comments from within macros in preprocessed output">,
diff --git a/clang/lib/Driver/ToolChains/Gnu.cpp b/clang/lib/Driver/ToolChains/Gnu.cpp
index 9fb99145d3b909e..44b92a879a3a8c1 100644
--- a/clang/lib/Driver/ToolChains/Gnu.cpp
+++ b/clang/lib/Driver/ToolChains/Gnu.cpp
@@ -2130,6 +2130,14 @@ void Generic_GCC::GCCInstallationDetector::init(
     return;
   }
 
+  // If --gcc-triple is specified use this instead of trying to
+  // auto-detect a triple.
+  if (const Arg *A = Args.getLastArg(clang::driver::options::OPT_gcc_triple_EQ)) {
+    StringRef GCCTriple = A->getValue();
+    CandidateTripleAliases.clear();
+    CandidateTripleAliases.push_back(GCCTriple);
+  }
+
   // Compute the set of prefixes for our search.
   SmallVector<std::string, 8> Prefixes;
   StringRef GCCToolchainDir = getGCCToolchainDir(Args, D.SysRoot);
diff --git a/clang/test/Driver/Inputs/fedora_39_tree/usr/lib/gcc/x86_64-linux-gnu/13/crtbegin.o b/clang/test/Driver/Inputs/fedora_39_tree/usr/lib/gcc/x86_64-linux-gnu/13/crtbegin.o
new file mode 100644
index 000000000000000..e69de29bb2d1d64
diff --git a/clang/test/Driver/Inputs/fedora_39_tree/usr/lib/gcc/x86_64-linux-gnu/13/crtend.o b/clang/test/Driver/Inputs/fedora_39_tree/usr/lib/gcc/x86_64-linux-gnu/13/crtend.o
new file mode 100644
index 000000000000000..e69de29bb2d1d64
diff --git a/clang/test/Driver/Inputs/fedora_39_tree/usr/lib/gcc/x86_64-linux-gnu/13/crti.o b/clang/test/Driver/Inputs/fedora_39_tree/usr/lib/gcc/x86_64-linux-gnu/13/crti.o
new file mode 100644
index 000000000000000..e69de29bb2d1d64
diff --git a/clang/test/Driver/Inputs/fedora_39_tree/usr/lib/gcc/x86_64-linux-gnu/13/crtn.o b/clang/test/Driver/Inputs/fedora_39_tree/usr/lib/gcc/x86_64-linux-gnu/13/crtn.o
new file mode 100644
index 000000000000000..e69de29bb2d1d64
diff --git a/clang/test/Driver/Inputs/fedora_39_tree/usr/lib/gcc/x86_64-redhat-linux/13/crtbegin.o b/clang/test/Driver/Inputs/fedora_39_tree/usr/lib/gcc/x86_64-redhat-linux/13/crtbegin.o
new file mode 100644
index 000000000000000..e69de29bb2d1d64
diff --git a/clang/test/Driver/Inputs/fedora_39_tree/usr/lib/gcc/x86_64-redhat-linux/13/crtend.o b/clang/test/Driver/Inputs/fedora_39_tree/usr/lib/gcc/x86_64-redhat-linux/13/crtend.o
new file mode 100644
index 000000000000000..e69de29bb2d1d64
diff --git a/clang/test/Driver/Inputs/fedora_39_tree/usr/lib/gcc/x86_64-redhat-linux/13/crti.o b/clang/test/Driver/Inputs/fedora_39_tree/usr/lib/gcc/x86_64-redhat-linux/13/crti.o
new file mode 100644
index 000000000000000..e69de29bb2d1d64
diff --git a/clang/test/Driver/Inputs/fedora_39_tree/usr/lib/gcc/x86_64-redhat-linux/13/crtn.o b/clang/test/Driver/Inputs/fedora_39_tree/usr/lib/gcc/x86_64-redhat-linux/13/crtn.o
new file mode 100644
index 000000000000000..e69de29bb2d1d64
diff --git a/clang/test/Driver/gcc-prefix.cpp b/clang/test/Driver/gcc-prefix.cpp
new file mode 100644
index 000000000000000..ce1146dc1ded21d
--- /dev/null
+++ b/clang/test/Driver/gcc-prefix.cpp
@@ -0,0 +1,8 @@
+// UNSUPPORTED: system-windows
+//
+// RUN: %clang --target=x86_64-redhat-linux-gnu \
+// RUN: --sysroot=%S/Inputs/fedora_39_tree --gcc-triple=x86_64-redhat-linux -v 2>&1 | \
+// RUN: FileCheck %s
+//
+// CHECK: {{^}}Selected GCC installation:
+// CHECK: fedora_39_tree/usr/lib/gcc/x86_64-redhat-linux/13{{$}}