[flang] [clang] [flang][driver] Remove Fortain_main static library from linking stages (PR #75816)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-clang-driver

@llvm/pr-subscribers-clang

Author: Michael Klemm (mjklemm)

<details>
<summary>Changes</summary>

At present, when building static or shared libraries, Flang adds `-lFortran_main.a` (or `/WHOLEARCHIVE:Fortran.*.lib` pon Windows) to the link line.  This leads to the problem that `_QQmain` and `_QQEnvironmentDefaults` (as of the time of this PR) are symbols marked as used, while `main` is being defined.  This should not happen and this PR fixes this by detecting if `-shared` or `-static` is used on the Flang command line and removing the static `Fortran_main` library.

---
Full diff: https://github.com/llvm/llvm-project/pull/75816.diff


2 Files Affected:

- (modified) clang/lib/Driver/ToolChains/CommonArgs.cpp (+20) 
- (modified) flang/test/Driver/dynamic-linker.f90 (+6-2) 


``````````diff
diff --git a/clang/lib/Driver/ToolChains/CommonArgs.cpp b/clang/lib/Driver/ToolChains/CommonArgs.cpp
index 45901ee7157f77..05ebd42829c95d 100644
--- a/clang/lib/Driver/ToolChains/CommonArgs.cpp
+++ b/clang/lib/Driver/ToolChains/CommonArgs.cpp
@@ -1133,6 +1133,16 @@ static bool isWholeArchivePresent(const ArgList &Args) {
   return WholeArchiveActive;
 }
 
+/// Determine if driver is invoked to create a shared object library (-static)
+static bool isSharedLinkage(const ArgList &Args) {
+  return Args.hasArg(options::OPT_shared);
+}
+
+/// Determine if driver is invoked to create a static object library (-shared)
+static bool isStaticLinkage(const ArgList &Args) {
+  return Args.hasArg(options::OPT_static);
+}
+
 /// Add Fortran runtime libs for MSVC
 static void addFortranRuntimeLibsMSVC(const ArgList &Args,
                                       llvm::opt::ArgStringList &CmdArgs) {
@@ -1164,6 +1174,16 @@ static void addFortranRuntimeLibsMSVC(const ArgList &Args,
 // Add FortranMain runtime lib
 static void addFortranMain(const ToolChain &TC, const ArgList &Args,
                            llvm::opt::ArgStringList &CmdArgs) {
+  // 0. Shared-library linkage
+  // If we are attempting to link a library, we should not add
+  // -lFortran_main.a to the link line, as the `main` symbol is not
+  // required for a library and should also be provided by one of
+  // the translation units of the code that this shared library
+  // will be linked against eventually.
+  if (isSharedLinkage(Args) || isStaticLinkage(Args)) {
+    return;
+  }
+
   // 1. MSVC
   if (TC.getTriple().isKnownWindowsMSVCEnvironment()) {
     addFortranRuntimeLibsMSVC(Args, CmdArgs);
diff --git a/flang/test/Driver/dynamic-linker.f90 b/flang/test/Driver/dynamic-linker.f90
index df119c22a2ea51..af07e2483f93fa 100644
--- a/flang/test/Driver/dynamic-linker.f90
+++ b/flang/test/Driver/dynamic-linker.f90
@@ -3,18 +3,22 @@
 
 ! RUN: %flang -### --target=x86_64-linux-gnu -rpath /path/to/dir -shared \
 ! RUN:     -static %s 2>&1 | FileCheck \
-! RUN:     --check-prefixes=GNU-LINKER-OPTIONS %s
+! RUN:     --check-prefixes=GNU-LINKER-OPTIONS \
+! RUN:     --implicit-check-not=GNU-LINKER-OPTIONS-NOT %s
 ! RUN: %flang -### --target=x86_64-windows-msvc -rpath /path/to/dir -shared \
 ! RUN:     -static %s 2>&1 | FileCheck \
-! RUN:     --check-prefixes=MSVC-LINKER-OPTIONS %s
+! RUN:     --check-prefixes=MSVC-LINKER-OPTIONS \
+! RUN:     --implicit-check-not=MSVC-LINKER-OPTIONS-NOT %s
 
 ! TODO: Could the linker have an extension or a suffix?
 ! GNU-LINKER-OPTIONS: "{{.*}}ld{{(.exe)?}}"
 ! GNU-LINKER-OPTIONS-SAME: "-shared"
 ! GNU-LINKER-OPTIONS-SAME: "-static"
 ! GNU-LINKER-OPTIONS-SAME: "-rpath" "/path/to/dir"
+! GNU-LINKER-OPTIONS-NOT: "-lFortran_main.a"
 
 ! For MSVC, adding -static does not add any additional linker options.
 ! MSVC-LINKER-OPTIONS: "{{.*}}link{{(.exe)?}}"
 ! MSVC-LINKER-OPTIONS-SAME: "-dll"
 ! MSVC-LINKER-OPTIONS-SAME: "-rpath" "/path/to/dir"
+! MSVC-LINKER-OPTIONS-NOT: "/WHOLEARCHIVE:Fortran_main"

``````````

</details>


https://github.com/llvm/llvm-project/pull/75816