[Clang][Driver] Fix read-after-free when using /clang:

[aganea]

Summary

As described in https://bugs.llvm.org/show_bug.cgi?id=42501

Fixes PR42501

[rnk]

lgtm

clang/lib/Driver/Driver.cpp

Compilation *Driver::BuildCompilation(ArrayRef<const char *> ArgList) {
   // All arguments, from both config file and command line.
   InputArgList Args = std::move(HasConfigFile ? std::move(*CfgOptions)
                                               : std::move(*CLOptions));
 
   // The args for config files or /clang: flags belong to different InputArgList
   // objects than Args. This copies an Arg from one of those other InputArgLists
   // to the ownership of Args.
   auto appendOneArg = [&Args](const Arg *Opt, const Arg *BaseArg) {
-      unsigned Index = Args.MakeIndex(Opt->getSpelling());
-      Arg *Copy = new llvm::opt::Arg(Opt->getOption(), Opt->getSpelling(),
-                                     Index, BaseArg);
-      Copy->getValues() = Opt->getValues();
-      if (Opt->isClaimed())
-        Copy->claim();
-      Args.append(Copy);
+    Arg *Copy = new llvm::opt::Arg(Opt->getOption(), Args.getArgString(Index),
+    Copy->setOwnsValues(Opt->getOwnsValues());
+    Opt->setOwnsValues(false);
   };
 
   if (HasConfigFile)
     for (auto *Opt : *CLOptions) {
       if (Opt->getOption().matches(options::OPT_config))
         continue;
       const Arg *BaseArg = &Opt->getBaseArg();
       if (BaseArg == Opt)

clang/test/Driver/cl-options.c

 // NOCLANG-NOT: "--dependent-lib=msvcrt"
 
 // RUN: %clang_cl -O2 -MD /clang:-fno-slp-vectorize /clang:-MD /clang:-MF /clang:my_dependency_file.dep -### -- %s 2>&1 | FileCheck -check-prefix=CLANG %s
 // CLANG: "--dependent-lib=msvcrt"
 // CLANG-SAME: "-dependency-file" "my_dependency_file.dep"
 // CLANG-NOT: "--dependent-lib=libcmt"
 // CLANG-NOT: "-vectorize-slp"
 
+// Cover PR42501: clang-cl /clang: pass-through causes read-after-free with aliased options.
+// RUN: %clang_cl /clang:-save-temps /clang:-Wl,test1,test2 -### -- %s 2>&1 | FileCheck -check-prefix=SAVETEMPS %s
+// SAVETEMPS: "-save-temps=cwd"
+// SAVETEMPS: "test1" "test2"
+
 // Validate that the default triple is used when run an empty tools dir is specified
 // RUN: %clang_cl -vctoolsdir "" -### -- %s 2>&1 | FileCheck %s --check-prefix VCTOOLSDIR
 // VCTOOLSDIR: "-triple" "{{[a-zA-Z0-9_-]*}}-pc-windows-msvc19.11.0"
 
 // Validate that built-in include paths are based on the supplied path
 // RUN: %clang_cl -vctoolsdir "/fake" -### -- %s 2>&1 | FileCheck %s --check-prefix FAKEDIR
 // FAKEDIR: "-internal-isystem" "/fake{{/|\\\\}}include"
 // FAKEDIR: "-internal-isystem" "/fake{{/|\\\\}}atlmfc{{/|\\\\}}include"
 
 void f() { }