Add -mscrtlib cmdline option and support -static on Windows (#2041)

The default MS C runtime library doesn't depend on the `LINK_WITH_MSVCRT`
CMake variable anymore.

The user can freely choose among the 4 variants libcmt[d] / msvcrt[d] via
-mscrtlib or choose between static/dynamic release variant via -static.

LDC keeps on defaulting to the static release C runtime, so
`-static=false` or `-mscrtlib=msvcrt[d]` must be used explicitly in order
to link against the runtime DLLs.

driver/ldmd.cpp

@@ -210,11 +210,9 @@ Where:\n\
 "  -map             generate linker .map file\n"
 #endif
 "  -mcpu=<id>       generate instructions for architecture identified by 'id'\n\
-  -mcpu=?          list all architecture options\n"
-#if 0
-"  -mscrtlib=<name> MS C runtime library to reference from main/WinMain/DllMain\n"
-#endif
-"  -mv=<package.module>=<filespec>  use <filespec> as source file for <package.module>\n\
+  -mcpu=?          list all architecture options\n\
+  -mscrtlib=<name> MS C runtime library to reference from main/WinMain/DllMain\n\
+  -mv=<package.module>=<filespec>  use <filespec> as source file for <package.module>\n\
   -noboundscheck   no array bounds checking (deprecated, use -boundscheck=off)\n\
   -O               optimize\n\
   -o-              do not write object file\n\
@@ -421,9 +419,10 @@ void translateArgs(size_t originalArgc, char **originalArgv,
        */
       else if (strcmp(p + 1, "m32mscoff") == 0) {
         ldcArgs.push_back("-m32");
-      } else if (strncmp(p + 1, "mscrtlib=", 9) == 0) {
-        goto Lnot_in_ldc;
-      } else if (strcmp(p + 1, "profile") == 0) {
+      }
+      /* -mscrtlib
+       */
+      else if (strcmp(p + 1, "profile") == 0) {
         goto Lnot_in_ldc;
       }
       /* -v

driver/linker.cpp

@@ -39,6 +39,12 @@ static llvm::cl::opt<bool> staticFlag(
         "Create a statically linked binary, including all system dependencies"),
     llvm::cl::ZeroOrMore);
 
+static llvm::cl::opt<std::string> mscrtlib(
+    "mscrtlib",
+    llvm::cl::desc(
+        "MS C runtime library to link against (libcmt[d] / msvcrt[d])"),
+    llvm::cl::value_desc("name"), llvm::cl::ZeroOrMore);
+
 static llvm::cl::opt<std::string>
     ltoLibrary("flto-binary",
                llvm::cl::desc("Set the linker LTO plugin library file (e.g. "
@@ -280,7 +286,7 @@ static void appendObjectFiles(std::vector<std::string> &args) {
 
 static std::string gExePath;
 
-static int linkObjToBinaryGcc(bool sharedLib, bool fullyStatic) {
+static int linkObjToBinaryGcc(bool sharedLib) {
   Logger::println("*** Linking executable ***");
 
   // find gcc for linking
@@ -317,7 +323,7 @@ static int linkObjToBinaryGcc(bool sharedLib, bool fullyStatic) {
     args.push_back("-shared");
   }
 
-  if (fullyStatic) {
+  if (staticFlag) {
     args.push_back("-static");
   }
 
@@ -489,6 +495,26 @@ static int linkObjToBinaryGcc(bool sharedLib, bool fullyStatic) {
 
 //////////////////////////////////////////////////////////////////////////////
 
+static void addMscrtLibs(std::vector<std::string> &args) {
+  llvm::StringRef mscrtlibName = mscrtlib;
+  if (mscrtlibName.empty()) {
+    // default to static release variant
+    mscrtlibName =
+        staticFlag || staticFlag.getNumOccurrences() == 0 ? "libcmt" : "msvcrt";
+  }
+
+  args.push_back(("/DEFAULTLIB:" + mscrtlibName).str());
+
+  const bool isStatic = mscrtlibName.startswith_lower("libcmt");
+  const bool isDebug =
+      mscrtlibName.endswith_lower("d") || mscrtlibName.endswith_lower("d.lib");
+
+  const llvm::StringRef prefix = isStatic ? "lib" : "";
+  const llvm::StringRef suffix = isDebug ? "d" : "";
+
+  args.push_back(("/DEFAULTLIB:" + prefix + "vcruntime" + suffix).str());
+}
+
 static int linkObjToBinaryMSVC(bool sharedLib) {
   Logger::println("*** Linking executable ***");
 
@@ -528,6 +554,9 @@ static int linkObjToBinaryMSVC(bool sharedLib) {
     args.push_back("/OPT:ICF");
   }
 
+  // add C runtime libs
+  addMscrtLibs(args);
+
   // specify creation of DLL
   if (sharedLib) {
     args.push_back("/DLL");
@@ -604,11 +633,10 @@ static int linkObjToBinaryMSVC(bool sharedLib) {
 
 int linkObjToBinary() {
   if (global.params.targetTriple->isWindowsMSVCEnvironment()) {
-    // TODO: Choose dynamic/static MSVCRT version based on staticFlag?
     return linkObjToBinaryMSVC(global.params.dll);
   }
 
-  return linkObjToBinaryGcc(global.params.dll, staticFlag);
+  return linkObjToBinaryGcc(global.params.dll);
 }
 
 //////////////////////////////////////////////////////////////////////////////

runtime/CMakeLists.txt

@@ -15,9 +15,6 @@ set(BUILD_SHARED_LIBS     AUTO                                      CACHE STRING
 set(D_FLAGS               -w                                        CACHE STRING  "Runtime build flags, separated by ;")
 set(D_FLAGS_DEBUG         -g;-link-debuglib                         CACHE STRING  "Runtime build flags (debug libraries), separated by ;")
 set(D_FLAGS_RELEASE       -O3;-release                              CACHE STRING  "Runtime build flags (release libraries), separated by ;")
-if(MSVC)
-    set(LINK_WITH_MSVCRT  OFF                                       CACHE BOOL    "Link with MSVCRT.lib (DLL) instead of LIBCMT.lib (static)")
-endif()
 
 set(CMAKE_INSTALL_LIBDIR ${CMAKE_INSTALL_PREFIX}/lib${LIB_SUFFIX})
 
@@ -246,17 +243,10 @@ endforeach()
 # of what the user chose for LDC itself.
 # 1) Set up CMAKE_C_FLAGS_RELEASE
 if(MSVC)
-    if(NOT LINK_WITH_MSVCRT)
-        string(REGEX REPLACE "(^| )[/-]MD( |$)" "\\2" CMAKE_C_FLAGS_RELEASE "${CMAKE_C_FLAGS_RELEASE}")
-        if(NOT CMAKE_C_FLAGS_RELEASE MATCHES "(^| )[/-]MT( |$)")
-            append("/MT" CMAKE_C_FLAGS_RELEASE)
-        endif()
-    else()
-        string(REGEX REPLACE "(^| )[/-]MT( |$)" "\\2" CMAKE_C_FLAGS_RELEASE "${CMAKE_C_FLAGS_RELEASE}")
-        if(NOT CMAKE_C_FLAGS_RELEASE MATCHES "(^| )[/-]MD( |$)")
-            append("/MD" CMAKE_C_FLAGS_RELEASE)
-        endif()
-    endif()
+    # Omit all references to the default C runtime libs.
+    # We want to be able to link against all 4 C runtime variants (libcmt[d] / msvcrt[d]).
+    string(REGEX REPLACE "(^| )[/-]M[TD]d?( |$)" "\\2" CMAKE_C_FLAGS_RELEASE "${CMAKE_C_FLAGS_RELEASE}")
+    append("/MT /Zl" CMAKE_C_FLAGS_RELEASE)
     # warning C4996: zlib uses 'deprecated' POSIX names
     append("/wd4996" CMAKE_C_FLAGS_RELEASE)
 endif()

runtime/druntime

@@ -1 +1 @@
-Subproject commit d91c32d44def323910a5e22d9a9739997f80b893
+Subproject commit 8414f932691e01dc6c174b88f67ffd6e21ba7fcc