[Driver] Use paths explicitly provided by the -L option before default paths

[atanasyan]

Summary

User should be able to override default search paths using the -L option.

[davide]

LGTM

[atanasyan]

Thanks for review.

Closed by commit rL230679.

lib/Driver/GnuLdDriver.cpp

bool GnuLdDriver::parse(int argc, const char *argv[],
   for (auto unknownArg : parsedArgs->filtered(OPT_UNKNOWN))
     diag << "warning: ignoring unknown argument: "
          << unknownArg->getValue() << "\n";
 
   // Set sys root path.
   if (auto *arg = parsedArgs->getLastArg(OPT_sysroot))
     ctx->setSysroot(arg->getValue());
 
-  // Add the default search directory specific to the target.
-  if (!parsedArgs->hasArg(OPT_nostdlib))
-    addPlatformSearchDirs(*ctx, triple, baseTriple);
-
   // Handle --demangle option(For compatibility)
   if (parsedArgs->hasArg(OPT_demangle))
     ctx->setDemangleSymbols(true);
 
   // Handle --no-demangle option.
   if (parsedArgs->hasArg(OPT_no_demangle))
     ctx->setDemangleSymbols(false);
 
if (auto *arg = parsedArgs->getLastArg(OPT_fini))
     ctx->setFiniFunction(arg->getValue());
 
   if (auto *arg = parsedArgs->getLastArg(OPT_output_filetype))
     ctx->setOutputFileType(arg->getValue());
 
   for (auto *arg : parsedArgs->filtered(OPT_L))
     ctx->addSearchPath(arg->getValue());
 
+  // Add the default search directory specific to the target.
+  if (!parsedArgs->hasArg(OPT_nostdlib))
+    addPlatformSearchDirs(*ctx, triple, baseTriple);
+
   for (auto *arg : parsedArgs->filtered(OPT_u))
     ctx->addInitialUndefinedSymbol(arg->getValue());
 
   for (auto *arg : parsedArgs->filtered(OPT_defsym)) {
     StringRef sym, target;
     uint64_t addr;
     if (parseDefsymAsAbsolute(arg->getValue(), sym, addr)) {
       ctx->addInitialAbsoluteSymbol(sym, addr);

test/Driver/Inputs/libtest.a

+!<arch>

test/Driver/def-lib-search.test

+# Check that search paths explicitly provided by the -L option
+# are used in search before default paths. 
+
+RUN: not lld -flavor gnu -target x86_64 -t -ltest \
+RUN:         --sysroot=%p/Inputs -L%p/Inputs 2> %t
+RUN: FileCheck %s < %t
+
+CHECK: {{[^ ]+}}{{[\\/]}}Inputs{{[\\/]}}libtest.a