[clang] [clang][mingw] Try both native and ARM64EC triples when looking for a sysroot on the ARM64EC target (PR #210017)

[Jacek Caban via cfe-commits]

https://github.com/cjacek created https://github.com/llvm/llvm-project/pull/210017

Similarly to MSVC, a MinGW toolchain may provide support for both ARM64 and ARM64EC in a single sysroot. Structuring the toolchain this way has the additional advantage of seamlessly supporting linking ARM64X images.

Support this configuration in findClangRelativeSysroot.

>From 11c9f0b1d73b4084a93882c3733128ad49f6ac5b Mon Sep 17 00:00:00 2001
From: Jacek Caban <jacek at codeweavers.com>
Date: Wed, 15 Jul 2026 00:43:06 +0200
Subject: [PATCH] [clang][mingw] Try both native and ARM64EC triples when
 looking for a sysroot on the ARM64EC target

Similarly to MSVC, a MinGW toolchain may provide support for both ARM64 and ARM64EC
in a single sysroot. Structuring the toolchain this way has the additional advantage
of seamlessly supporting linking ARM64X images.

Support this configuration in findClangRelativeSysroot.
---
 clang/lib/Driver/ToolChains/MinGW.cpp | 15 +++++++++++++++
 clang/test/Driver/mingw-sysroot.cpp   | 14 ++++++++++++++
 2 files changed, 29 insertions(+)

diff --git a/clang/lib/Driver/ToolChains/MinGW.cpp b/clang/lib/Driver/ToolChains/MinGW.cpp
index 7fe5be92012ee..65120931d8181 100644
--- a/clang/lib/Driver/ToolChains/MinGW.cpp
+++ b/clang/lib/Driver/ToolChains/MinGW.cpp
@@ -476,11 +476,26 @@ findClangRelativeSysroot(const Driver &D, const llvm::Triple &LiteralTriple,
                          const llvm::Triple &T, std::string &SubdirName) {
   llvm::SmallVector<llvm::SmallString<32>, 4> Subdirs;
   Subdirs.emplace_back(LiteralTriple.str());
+  // On ARM64EC targets, also try native aarch64 sysroot, which may contain
+  // support for both targets.
+  if (LiteralTriple.isWindowsArm64EC()) {
+    llvm::Triple NativeTriple(LiteralTriple);
+    NativeTriple.setArchName("aarch64");
+    Subdirs.emplace_back(NativeTriple.str());
+  }
   Subdirs.emplace_back(T.str());
   Subdirs.emplace_back(T.getArchName());
   Subdirs.back() += "-w64-mingw32";
   Subdirs.emplace_back(T.getArchName());
   Subdirs.back() += "-w64-mingw32ucrt";
+  if (T.isWindowsArm64EC()) {
+    llvm::Triple NativeTriple(T);
+    NativeTriple.setArchName("aarch64");
+    Subdirs.emplace_back(NativeTriple.str());
+
+    Subdirs.emplace_back("aarch64-w64-mingw32");
+    Subdirs.emplace_back("aarch64-w64-mingw32ucrt");
+  }
   StringRef ClangRoot = llvm::sys::path::parent_path(D.Dir);
   StringRef Sep = llvm::sys::path::get_separator();
   for (StringRef CandidateSubdir : Subdirs) {
diff --git a/clang/test/Driver/mingw-sysroot.cpp b/clang/test/Driver/mingw-sysroot.cpp
index 8e46d23c1782d..3f21cadd033be 100644
--- a/clang/test/Driver/mingw-sysroot.cpp
+++ b/clang/test/Driver/mingw-sysroot.cpp
@@ -10,8 +10,11 @@
 // RUN: rm -rf %t.dir/testroot-clang
 // RUN: mkdir -p %t.dir/testroot-clang/bin
 // RUN: ln -s %clang %t.dir/testroot-clang/bin/x86_64-w64-mingw32-clang
+// RUN: ln -s %clang %t.dir/testroot-clang/bin/aarch64-w64-mingw32-clang
+// RUN: ln -s %clang %t.dir/testroot-clang/bin/arm64ec-w64-mingw32-clang
 // RUN: ln -s %S/Inputs/mingw_ubuntu_posix_tree/usr/x86_64-w64-mingw32 %t.dir/testroot-clang/x86_64-w64-mingw32
 // RUN: ln -s %S/Inputs/mingw_arch_tree/usr/i686-w64-mingw32 %t.dir/testroot-clang/i686-w64-mingw32
+// RUN: ln -s %S/Inputs/mingw_ubuntu_posix_tree/usr/x86_64-w64-mingw32 %t.dir/testroot-clang/aarch64-w64-mingw32
 
 // RUN: rm -rf %t.dir/testroot-clang-native
 // RUN: mkdir -p %t.dir/testroot-clang-native/bin
@@ -23,6 +26,7 @@
 // RUN: mkdir -p %t.dir/testroot-custom-triple/bin
 // RUN: ln -s %clang %t.dir/testroot-custom-triple/bin/clang
 // RUN: ln -s %S/Inputs/mingw_ubuntu_posix_tree/usr/x86_64-w64-mingw32 %t.dir/testroot-custom-triple/x86_64-w64-mingw32foo
+// RUN: ln -s %S/Inputs/mingw_ubuntu_posix_tree/usr/x86_64-w64-mingw32 %t.dir/testroot-custom-triple/aarch64-w64-mingw32foo
 
 // If we find a gcc in the path with the right triplet prefix, pick that as
 // sysroot:
@@ -103,3 +107,13 @@
 
 // RUN: %t.dir/testroot-custom-triple/bin/clang -no-canonical-prefixes --target=x86_64-w64-mingw32foo -rtlib=compiler-rt -stdlib=libstdc++ --sysroot="" -c -### %s 2>&1 | FileCheck -check-prefix=CHECK_TESTROOT_CUSTOM_TRIPLE %s
 // CHECK_TESTROOT_CUSTOM_TRIPLE: "{{[^"]+}}/testroot-custom-triple{{/|\\\\}}x86_64-w64-mingw32foo{{/|\\\\}}include"
+
+// Check that the arm64ec target uses the aarch64 sysroot if a separate arm64ec sysroot is not found.
+
+// RUN: %t.dir/testroot-clang/bin/aarch64-w64-mingw32-clang -no-canonical-prefixes --target=aarch64-w64-mingw32 -rtlib=compiler-rt -stdlib=libstdc++ --sysroot="" -c -### %s 2>&1 | FileCheck -check-prefix=CHECK_TESTROOT_CLANG_AARCH64 %s
+// RUN: %t.dir/testroot-clang/bin/arm64ec-w64-mingw32-clang -no-canonical-prefixes --target=arm64ec-w64-mingw32 -rtlib=compiler-rt -stdlib=libstdc++ --sysroot="" -c -### %s 2>&1 | FileCheck -check-prefix=CHECK_TESTROOT_CLANG_AARCH64 %s
+// CHECK_TESTROOT_CLANG_AARCH64: "{{[^"]+}}/testroot-clang{{/|\\\\}}aarch64-w64-mingw32{{/|\\\\}}include"
+
+// RUN: %t.dir/testroot-custom-triple/bin/clang -no-canonical-prefixes --target=aarch64-w64-mingw32foo -rtlib=compiler-rt -stdlib=libstdc++ --sysroot="" -c -### %s 2>&1 | FileCheck -check-prefix=CHECK_TESTROOT_CUSTOM_TRIPLE_AARCH64 %s
+// RUN: %t.dir/testroot-custom-triple/bin/clang -no-canonical-prefixes --target=arm64ec-w64-mingw32foo -rtlib=compiler-rt -stdlib=libstdc++ --sysroot="" -c -### %s 2>&1 | FileCheck -check-prefix=CHECK_TESTROOT_CUSTOM_TRIPLE_AARCH64 %s
+// CHECK_TESTROOT_CUSTOM_TRIPLE_AARCH64: "{{[^"]+}}/testroot-custom-triple{{/|\\\\}}aarch64-w64-mingw32foo{{/|\\\\}}include"