[LLD][MinGW] Implement --dll-search-prefix option

Author: mati865

lld/MinGW/Driver.cpp

@@ -139,8 +139,9 @@ static std::optional<std::string> findFile(StringRef path1,
 }
 
 // This is for -lfoo. We'll look for libfoo.dll.a or libfoo.a from search paths.
-static std::string
-searchLibrary(StringRef name, ArrayRef<StringRef> searchPaths, bool bStatic) {
+static std::string searchLibrary(StringRef name,
+                                 ArrayRef<StringRef> searchPaths, bool bStatic,
+                                 StringRef dllPrefix = "") {
   if (name.starts_with(":")) {
     for (StringRef dir : searchPaths)
       if (std::optional<std::string> s = findFile(dir, name.substr(1)))
@@ -161,6 +162,11 @@ searchLibrary(StringRef name, ArrayRef<StringRef> searchPaths, bool bStatic) {
     if (std::optional<std::string> s = findFile(dir, name + ".lib"))
       return *s;
     if (!bStatic) {
+      if (!dllPrefix.empty()) {
+        if (std::optional<std::string> s =
+                findFile(dir, dllPrefix + name + ".dll"))
+          return *s;
+      }
       if (std::optional<std::string> s = findFile(dir, "lib" + name + ".dll"))
         return *s;
       if (std::optional<std::string> s = findFile(dir, name + ".dll"))
@@ -545,6 +551,10 @@ bool link(ArrayRef<const char *> argsArr, llvm::raw_ostream &stdoutOS,
     add("-libpath:" + StringRef(a->getValue()));
   }
 
+  StringRef dllPrefix;
+  if (auto *a = args.getLastArg(OPT_dll_search_prefix))
+    dllPrefix = a->getValue();
+
   StringRef prefix = "";
   bool isStatic = false;
   for (auto *a : args) {
@@ -556,7 +566,8 @@ bool link(ArrayRef<const char *> argsArr, llvm::raw_ostream &stdoutOS,
         add(prefix + StringRef(a->getValue()));
       break;
     case OPT_l:
-      add(prefix + searchLibrary(a->getValue(), searchPaths, isStatic));
+      add(prefix +
+          searchLibrary(a->getValue(), searchPaths, isStatic, dllPrefix));
       break;
     case OPT_whole_archive:
       prefix = "-wholearchive:";

lld/MinGW/Options.td

@@ -65,6 +65,8 @@ def disable_runtime_pseudo_reloc: F<"disable-runtime-pseudo-reloc">,
     HelpText<"Don't do automatic imports that require runtime fixups">;
 def disable_stdcall_fixup: F<"disable-stdcall-fixup">,
     HelpText<"Don't resolve stdcall/fastcall/vectorcall to undecorated symbols">;
+defm dll_search_prefix: EEq<"dll-search-prefix",
+    "Prefer DLL with this prefix if importlib is missing">;
 defm dynamicbase: B_disable<"dynamicbase", "Enable ASLR", "Disable ASLR">;
 def enable_auto_import: F<"enable-auto-import">,
     HelpText<"Automatically import data symbols from other DLLs where needed">;