[flang] [clang] [flang][windows] Add option to link against specific MSVC CRT (PR #70833)

[David Truby via cfe-commits]

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@@ -976,12 +976,46 @@ bool tools::addOpenMPRuntime(ArgStringList &CmdArgs, const ToolChain &TC,
   return true;
 }
 
-void tools::addFortranRuntimeLibs(const ToolChain &TC,
+void tools::addFortranRuntimeLibs(const ToolChain &TC, const ArgList &Args,
                                   llvm::opt::ArgStringList &CmdArgs) {
   if (TC.getTriple().isKnownWindowsMSVCEnvironment()) {
-    CmdArgs.push_back("Fortran_main.lib");
-    CmdArgs.push_back("FortranRuntime.lib");
-    CmdArgs.push_back("FortranDecimal.lib");
+    CmdArgs.push_back(Args.MakeArgString(
+        "/DEFAULTLIB:" + TC.getCompilerRTBasename(Args, "builtins")));
+    unsigned RTOptionID = options::OPT__SLASH_MT;
+    if (auto *rtl = Args.getLastArg(options::OPT_fms_runtime_lib_EQ)) {
+      RTOptionID = llvm::StringSwitch<unsigned>(rtl->getValue())
+                       .Case("static", options::OPT__SLASH_MT)
+                       .Case("static_dbg", options::OPT__SLASH_MTd)
+                       .Case("dll", options::OPT__SLASH_MD)
+                       .Case("dll_dbg", options::OPT__SLASH_MDd)
+                       .Default(options::OPT__SLASH_MT);
+    }
+    switch (RTOptionID) {
+    case options::OPT__SLASH_MT:
+      CmdArgs.push_back("/DEFAULTLIB:libcmt");
+      CmdArgs.push_back("Fortran_main.static.lib");
+      CmdArgs.push_back("FortranRuntime.static.lib");
+      CmdArgs.push_back("FortranDecimal.static.lib");
+      break;
+    case options::OPT__SLASH_MTd:
+      CmdArgs.push_back("/DEFAULTLIB:libcmtd");
+      CmdArgs.push_back("Fortran_main.static_debug.lib");
+      CmdArgs.push_back("FortranRuntime.static_debug.lib");
+      CmdArgs.push_back("FortranDecimal.static_debug.lib");
+      break;
+    case options::OPT__SLASH_MD:
+      CmdArgs.push_back("/DEFAULTLIB:msvcrt");
+      CmdArgs.push_back("Fortran_main.dynamic.lib");
+      CmdArgs.push_back("FortranRuntime.dynamic.lib");
+      CmdArgs.push_back("FortranDecimal.dynamic.lib");
+      break;
----------------
DavidTruby wrote:

Is there a way to add defaultlib directives using a CLI tool, or do they _have_ to be added when the compiler creates the object file? The main issue is we have an MLIR step in between flang and LLVM IR and I don't believe MLIR supports the attributes for setting these defaultlib directives yet, so implimenting that might be quite a lot of work... It's not so much that we would have difficulty adding the specific defaultlib directive we need, as that we'd have an issue adding any of them.

https://github.com/llvm/llvm-project/pull/70833