[clang] [llvm] [Flang] Search flang_rt in clang_rt path (PR #151954)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Michael Kruse (Meinersbur)

<details>
<summary>Changes</summary>

clang_rt has two separate systems for find its location (simplified):

 * `getRuntimePath()`, e.g. `../lib/clang/22/lib/x86_64-pc-windows-msvc`, used with `LLVM_ENABLE_PER_TARGET_RUNTIME_DIR=1`
 * `getCompilerRTPath()`,  e.g. `../lib/clang/22/lib/windows`, used with `LLVM_ENABLE_PER_TARGET_RUNTIME_DIR=0`

To simplify the search path, Flang-RT normally assumes only `getRuntimePath()`, i.e. ignoring `LLVM_ENABLE_PER_TARGET_RUNTIME_DIR`. There is an exception for Apple Darwin where `getRuntimePath()` returns nothing. We fall back to `getCompilerRTPath()` instead since LLVM_ENABLE_PER_TARGET_RUNTIME_DIR is also ignored in the flang-rt/compiler-rt CMake code. Since only `getRuntimePath()` is automatically added to the linker command line, we add the path explicitly when linking flang_rt.

Fixes #<!-- -->151031 

---
Full diff: https://github.com/llvm/llvm-project/pull/151954.diff


1 Files Affected:

- (modified) clang/lib/Driver/ToolChain.cpp (+21-8) 


``````````diff
diff --git a/clang/lib/Driver/ToolChain.cpp b/clang/lib/Driver/ToolChain.cpp
index 25c6b5a486fd5..7667dbddb0ca2 100644
--- a/clang/lib/Driver/ToolChain.cpp
+++ b/clang/lib/Driver/ToolChain.cpp
@@ -855,17 +855,30 @@ void ToolChain::addFortranRuntimeLibs(const ArgList &Args,
 
 void ToolChain::addFortranRuntimeLibraryPath(const llvm::opt::ArgList &Args,
                                              ArgStringList &CmdArgs) const {
-  // Default to the <driver-path>/../lib directory. This works fine on the
-  // platforms that we have tested so far. We will probably have to re-fine
-  // this in the future. In particular, on some platforms, we may need to use
-  // lib64 instead of lib.
+  auto AddLibSearchPathIfExists = [&](const Twine &Path) {
+    // Linker may emit warnings about non-existing directories
+    if (!llvm::sys::fs::is_directory(Path))
+      return;
+
+    if (getTriple().isKnownWindowsMSVCEnvironment())
+      CmdArgs.push_back(Args.MakeArgString("-libpath:" + Path));
+    else
+      CmdArgs.push_back(Args.MakeArgString("-L" + Path));
+  };
+
+  // Search for flang_rt.* at the same location as clang_rt.* with
+  // LLVM_ENABLE_PER_TARGET_RUNTIME_DIR=0. On most platforms, flang_rt is
+  // located at the path returned by getRuntimePath() which is already added to
+  // the library search path. This exception is for Apple-Darwin.
+  AddLibSearchPathIfExists(getCompilerRTPath());
+
+  // Fall back to the non-resource directory <driver-path>/../lib. We will
+  // probably have to refine this in the future. In particular, on some
+  // platforms, we may need to use lib64 instead of lib.
   SmallString<256> DefaultLibPath =
       llvm::sys::path::parent_path(getDriver().Dir);
   llvm::sys::path::append(DefaultLibPath, "lib");
-  if (getTriple().isKnownWindowsMSVCEnvironment())
-    CmdArgs.push_back(Args.MakeArgString("-libpath:" + DefaultLibPath));
-  else
-    CmdArgs.push_back(Args.MakeArgString("-L" + DefaultLibPath));
+  AddLibSearchPathIfExists(DefaultLibPath);
 }
 
 void ToolChain::addFlangRTLibPath(const ArgList &Args,

``````````

</details>


https://github.com/llvm/llvm-project/pull/151954