Add an option to correct driver's fallback position

Author: pogo59

clang/include/clang/Driver/Options.td

@@ -5541,6 +5541,12 @@ def fno_rtlib_defaultlib : Flag<["-"], "fno-rtlib-defaultlib">,
                       Visibility<[ClangOption, CLOption]>,
                       Group<f_Group>,
                       HelpText<"On Windows, do not emit /defaultlib: directives to link compiler-rt libraries">;
+def frtlib_per_target :
+  Flag<["-"], "frtlib-per-target">, Visibility<[ClangOption, CLOption]>, Group<f_Group>,
+  HelpText<"Compiler-rt libraries are in per-target directories">;
+def fno_rtlib_per_target :
+  Flag<["-"], "fno-rtlib-per-target">, Visibility<[ClangOption, CLOption]>, Group<f_Group>,
+  HelpText<"Compiler-rt libraries are in one directory and have target-specific names">;
 def offload_add_rpath: Flag<["--"], "offload-add-rpath">,
   Flags<[NoArgumentUnused]>,
   Alias<frtlib_add_rpath>;

clang/lib/Driver/ToolChain.cpp

@@ -685,8 +685,10 @@ std::string ToolChain::getCompilerRT(const ArgList &Args, StringRef Component,
       Path = P;
   }
   // Some targets default to the old layout.
-  if (getTriple().isOSAIX() || getTriple().isPS() ||
-      getTriple().isWindowsMSVCEnvironment())
+  bool UseOldLayout =
+      getTriple().isOSAIX() || getTriple().isPS() || getTriple().isOSWindows();
+  if (!Args.hasFlag(options::OPT_frtlib_per_target,
+                    options::OPT_fno_rtlib_per_target, !UseOldLayout))
     Path.clear();
 
   // Check the filename for the old layout if the new one does not exist.

clang/lib/Driver/ToolChains/Clang.cpp

@@ -6225,6 +6225,10 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
     }
   }
 
+  // Don't warn about compiler-rt layout options.
+  Args.ClaimAllArgs(options::OPT_frtlib_per_target);
+  Args.ClaimAllArgs(options::OPT_fno_rtlib_per_target);
+
   // Warn about ignored options to clang.
   for (const Arg *A :
        Args.filtered(options::OPT_clang_ignored_gcc_optimization_f_Group)) {

clang/test/Driver/sanitizer-ld.c

@@ -798,6 +798,21 @@
 // CHECK-CFI-STATS-WIN64: "--dependent-lib=clang_rt.stats{{(-x86_64)?}}.lib"
 // CHECK-CFI-STATS-WIN64: "--linker-option=/include:__sanitizer_stats_register"
 
+// RUN: not %clang -fsanitize=cfi -fsanitize-stats -### %s 2>&1 \
+// RUN:     --target=x86_64-pc-windows \
+// RUN:     -resource-dir=%S/Inputs/resource_dir \
+// RUN:     --sysroot=%S/Inputs/basic_linux_tree \
+// RUN:     -frtlib-per-target \
+// RUN:   | FileCheck --check-prefix=CHECK-CFI-STATS-RTLIB %s -DSUFFIX=
+// RUN: not %clang -fsanitize=cfi -fsanitize-stats -### %s 2>&1 \
+// RUN:     --target=x86_64-pc-windows \
+// RUN:     -resource-dir=%S/Inputs/resource_dir \
+// RUN:     --sysroot=%S/Inputs/basic_linux_tree \
+// RUN:     -fno-rtlib-per-target \
+// RUN:   | FileCheck --check-prefix=CHECK-CFI-STATS-RTLIB %s -DSUFFIX=-x86_64
+// CHECK-CFI-STATS-RTLIB: "--dependent-lib=clang_rt.stats_client[[SUFFIX]].lib"
+// CHECK-CFI-STATS-RTLIB: "--dependent-lib=clang_rt.stats[[SUFFIX]].lib"
+
 // RUN: not %clang -fsanitize=cfi -fsanitize-stats -### %s 2>&1 \
 // RUN:     --target=i686-pc-windows \
 // RUN:     --sysroot=%S/Inputs/basic_linux_tree \