Index: clang/lib/Driver/ToolChains/Arch/RISCV.h
===================================================================
--- clang/lib/Driver/ToolChains/Arch/RISCV.h
+++ clang/lib/Driver/ToolChains/Arch/RISCV.h
@@ -26,6 +26,17 @@
                       const llvm::Triple &Triple);
 StringRef getRISCVArch(const llvm::opt::ArgList &Args,
                        const llvm::Triple &Triple);
+void findRISCVBareMetalMultilibs(const Driver &D,
+                                 const llvm::Triple &TargetTriple,
+                                 StringRef Path, const llvm::opt::ArgList &Args,
+                                 MultilibSet &Multilibs,
+                                 Multilib &SelectedMultilib,
+                                 bool ShouldFilterNonExistent);
+void findRISCVMultilibs(const Driver &D,
+                        const llvm::Triple &TargetTriple, StringRef Path,
+                        const llvm::opt::ArgList &Args,
+                        MultilibSet &Multilibs, Multilib &SelectedMultilib,
+                        bool ShouldFilterNonExistent);
 } // end namespace riscv
 } // namespace tools
 } // end namespace driver
Index: clang/lib/Driver/ToolChains/Arch/RISCV.cpp
===================================================================
--- clang/lib/Driver/ToolChains/Arch/RISCV.cpp
+++ clang/lib/Driver/ToolChains/Arch/RISCV.cpp
@@ -14,6 +14,7 @@
 #include "llvm/Option/ArgList.h"
 #include "llvm/ADT/Optional.h"
 #include "llvm/Support/TargetParser.h"
+#include "llvm/Support/VirtualFileSystem.h"
 #include "llvm/Support/raw_ostream.h"
 #include "ToolChains/CommonArgs.h"
 
@@ -28,6 +29,19 @@
   StringRef Major;
   StringRef Minor;
 };
+
+// Filter to remove Multilibs that don't exist as a suffix to Path
+class FilterNonExistent {
+  StringRef Base, File;
+  llvm::vfs::FileSystem &VFS;
+
+public:
+  FilterNonExistent(StringRef Base, StringRef File, llvm::vfs::FileSystem &VFS)
+      : Base(Base), File(File), VFS(VFS) {}
+  bool operator()(const Multilib &M) {
+    return !VFS.exists(Base + M.gccSuffix() + File);
+  }
+};
 } // end anonymous namespace
 
 static StringRef getExtensionTypeDesc(StringRef Ext) {
@@ -655,3 +669,113 @@
       return "rv64imafdc";
   }
 }
+
+static Multilib makeMultilib(StringRef commonSuffix) {
+  return Multilib(commonSuffix, commonSuffix, commonSuffix);
+}
+
+void riscv::findRISCVBareMetalMultilibs(const Driver &D,
+                                        const llvm::Triple &TargetTriple,
+                                        StringRef Path,
+                                        const llvm::opt::ArgList &Args,
+                                        MultilibSet &Multilibs,
+                                        Multilib &SelectedMultilib,
+                                        bool ShouldFilterNonExistent) {
+  FilterNonExistent NonExistent(Path, "/crtbegin.o", D.getVFS());
+  struct RiscvMultilib {
+    StringRef march;
+    StringRef mabi;
+  };
+  // currently only support the set of multilibs like riscv-gnu-toolchain does.
+  // TODO: support MULTILIB_REUSE
+  constexpr RiscvMultilib RISCVMultilibSet[] = {
+      {"rv32i", "ilp32"},     {"rv32im", "ilp32"},     {"rv32iac", "ilp32"},
+      {"rv32imac", "ilp32"},  {"rv32imafc", "ilp32f"}, {"rv64imac", "lp64"},
+      {"rv64imafdc", "lp64d"}};
+
+  std::vector<Multilib> Ms;
+  for (auto Element : RISCVMultilibSet) {
+    // multilib path rule is ${march}/${mabi}
+    Ms.emplace_back(
+        makeMultilib((Twine(Element.march) + "/" + Twine(Element.mabi)).str())
+            .flag(Twine("+march=", Element.march).str())
+            .flag(Twine("+mabi=", Element.mabi).str()));
+  }
+  MultilibSet RISCVMultilibs =
+      MultilibSet()
+          .Either(ArrayRef<Multilib>(Ms));
+
+  if (ShouldFilterNonExistent)
+    RISCVMultilibs.FilterOut(NonExistent);
+
+  RISCVMultilibs.setFilePathsCallback([](const Multilib &M) {
+    return std::vector<std::string>(
+        {M.gccSuffix(),
+         "/../../../../riscv64-unknown-elf/lib" + M.gccSuffix(),
+         "/../../../../riscv32-unknown-elf/lib" + M.gccSuffix(),
+         // For clang
+         "/../../../riscv64-unknown-elf/lib" + M.gccSuffix(),
+         "/../../../riscv32-unknown-elf/lib" + M.gccSuffix()});
+  });
+
+  Multilib::flags_list Flags;
+  llvm::StringSet<> Added_ABIs;
+  StringRef ABIName = tools::riscv::getRISCVABI(Args, TargetTriple);
+  StringRef MArch = tools::riscv::getRISCVArch(Args, TargetTriple);
+  for (auto Element : RISCVMultilibSet) {
+    addMultilibFlag(MArch == Element.march,
+                    Twine("march=", Element.march).str().c_str(), Flags);
+    if (!Added_ABIs.count(Element.mabi)) {
+      Added_ABIs.insert(Element.mabi);
+      addMultilibFlag(ABIName == Element.mabi,
+                      Twine("mabi=", Element.mabi).str().c_str(), Flags);
+    }
+  }
+
+  if (RISCVMultilibs.select(Flags, SelectedMultilib))
+    Multilibs = RISCVMultilibs;
+}
+
+void riscv::findRISCVMultilibs(const Driver &D,
+                               const llvm::Triple &TargetTriple, StringRef Path,
+                               const llvm::opt::ArgList &Args,
+                               MultilibSet &Multilibs,
+                               Multilib &SelectedMultilib,
+                               bool ShouldFilterNonExistent) {
+  if (TargetTriple.getOS() == llvm::Triple::UnknownOS)
+    return findRISCVBareMetalMultilibs(D, TargetTriple, Path, Args, Multilibs,
+                                       SelectedMultilib,
+                                       ShouldFilterNonExistent);
+
+  FilterNonExistent NonExistent(Path, "/crtbegin.o", D.getVFS());
+  Multilib Ilp32 = makeMultilib("lib32/ilp32").flag("+m32").flag("+mabi=ilp32");
+  Multilib Ilp32f =
+      makeMultilib("lib32/ilp32f").flag("+m32").flag("+mabi=ilp32f");
+  Multilib Ilp32d =
+      makeMultilib("lib32/ilp32d").flag("+m32").flag("+mabi=ilp32d");
+  Multilib Lp64 = makeMultilib("lib64/lp64").flag("+m64").flag("+mabi=lp64");
+  Multilib Lp64f = makeMultilib("lib64/lp64f").flag("+m64").flag("+mabi=lp64f");
+  Multilib Lp64d = makeMultilib("lib64/lp64d").flag("+m64").flag("+mabi=lp64d");
+  MultilibSet RISCVMultilibs =
+      MultilibSet()
+          .Either({Ilp32, Ilp32f, Ilp32d, Lp64, Lp64f, Lp64d});
+
+  if (ShouldFilterNonExistent)
+    RISCVMultilibs.FilterOut(NonExistent);
+
+  Multilib::flags_list Flags;
+  bool IsRV64 = TargetTriple.getArch() == llvm::Triple::riscv64;
+  StringRef ABIName = tools::riscv::getRISCVABI(Args, TargetTriple);
+
+  addMultilibFlag(!IsRV64, "m32", Flags);
+  addMultilibFlag(IsRV64, "m64", Flags);
+  addMultilibFlag(ABIName == "ilp32", "mabi=ilp32", Flags);
+  addMultilibFlag(ABIName == "ilp32f", "mabi=ilp32f", Flags);
+  addMultilibFlag(ABIName == "ilp32d", "mabi=ilp32d", Flags);
+  addMultilibFlag(ABIName == "lp64", "mabi=lp64", Flags);
+  addMultilibFlag(ABIName == "lp64f", "mabi=lp64f", Flags);
+  addMultilibFlag(ABIName == "lp64d", "mabi=lp64d", Flags);
+
+  if (RISCVMultilibs.select(Flags, SelectedMultilib))
+    Multilibs = RISCVMultilibs;
+}
Index: clang/lib/Driver/ToolChains/Gnu.cpp
===================================================================
--- clang/lib/Driver/ToolChains/Gnu.cpp
+++ clang/lib/Driver/ToolChains/Gnu.cpp
@@ -1521,97 +1521,6 @@
   return false;
 }
 
-static void findRISCVBareMetalMultilibs(const Driver &D,
-                                        const llvm::Triple &TargetTriple,
-                                        StringRef Path, const ArgList &Args,
-                                        DetectedMultilibs &Result) {
-  FilterNonExistent NonExistent(Path, "/crtbegin.o", D.getVFS());
-  struct RiscvMultilib {
-    StringRef march;
-    StringRef mabi;
-  };
-  // currently only support the set of multilibs like riscv-gnu-toolchain does.
-  // TODO: support MULTILIB_REUSE
-  constexpr RiscvMultilib RISCVMultilibSet[] = {
-      {"rv32i", "ilp32"},     {"rv32im", "ilp32"},     {"rv32iac", "ilp32"},
-      {"rv32imac", "ilp32"},  {"rv32imafc", "ilp32f"}, {"rv64imac", "lp64"},
-      {"rv64imafdc", "lp64d"}};
-
-  std::vector<Multilib> Ms;
-  for (auto Element : RISCVMultilibSet) {
-    // multilib path rule is ${march}/${mabi}
-    Ms.emplace_back(
-        makeMultilib((Twine(Element.march) + "/" + Twine(Element.mabi)).str())
-            .flag(Twine("+march=", Element.march).str())
-            .flag(Twine("+mabi=", Element.mabi).str()));
-  }
-  MultilibSet RISCVMultilibs =
-      MultilibSet()
-          .Either(ArrayRef<Multilib>(Ms))
-          .FilterOut(NonExistent)
-          .setFilePathsCallback([](const Multilib &M) {
-            return std::vector<std::string>(
-                {M.gccSuffix(),
-                 "/../../../../riscv64-unknown-elf/lib" + M.gccSuffix(),
-                 "/../../../../riscv32-unknown-elf/lib" + M.gccSuffix()});
-          });
-
-
-  Multilib::flags_list Flags;
-  llvm::StringSet<> Added_ABIs;
-  StringRef ABIName = tools::riscv::getRISCVABI(Args, TargetTriple);
-  StringRef MArch = tools::riscv::getRISCVArch(Args, TargetTriple);
-  for (auto Element : RISCVMultilibSet) {
-    addMultilibFlag(MArch == Element.march,
-                    Twine("march=", Element.march).str().c_str(), Flags);
-    if (!Added_ABIs.count(Element.mabi)) {
-      Added_ABIs.insert(Element.mabi);
-      addMultilibFlag(ABIName == Element.mabi,
-                      Twine("mabi=", Element.mabi).str().c_str(), Flags);
-    }
-  }
-
-  if (RISCVMultilibs.select(Flags, Result.SelectedMultilib))
-    Result.Multilibs = RISCVMultilibs;
-}
-
-static void findRISCVMultilibs(const Driver &D,
-                               const llvm::Triple &TargetTriple, StringRef Path,
-                               const ArgList &Args, DetectedMultilibs &Result) {
-  if (TargetTriple.getOS() == llvm::Triple::UnknownOS)
-    return findRISCVBareMetalMultilibs(D, TargetTriple, Path, Args, Result);
-
-  FilterNonExistent NonExistent(Path, "/crtbegin.o", D.getVFS());
-  Multilib Ilp32 = makeMultilib("lib32/ilp32").flag("+m32").flag("+mabi=ilp32");
-  Multilib Ilp32f =
-      makeMultilib("lib32/ilp32f").flag("+m32").flag("+mabi=ilp32f");
-  Multilib Ilp32d =
-      makeMultilib("lib32/ilp32d").flag("+m32").flag("+mabi=ilp32d");
-  Multilib Lp64 = makeMultilib("lib64/lp64").flag("+m64").flag("+mabi=lp64");
-  Multilib Lp64f = makeMultilib("lib64/lp64f").flag("+m64").flag("+mabi=lp64f");
-  Multilib Lp64d = makeMultilib("lib64/lp64d").flag("+m64").flag("+mabi=lp64d");
-  MultilibSet RISCVMultilibs =
-      MultilibSet()
-          .Either({Ilp32, Ilp32f, Ilp32d, Lp64, Lp64f, Lp64d})
-          .FilterOut(NonExistent);
-
-  Multilib::flags_list Flags;
-  bool IsRV64 = TargetTriple.getArch() == llvm::Triple::riscv64;
-  StringRef ABIName = tools::riscv::getRISCVABI(Args, TargetTriple);
-
-  addMultilibFlag(!IsRV64, "m32", Flags);
-  addMultilibFlag(IsRV64, "m64", Flags);
-  addMultilibFlag(ABIName == "ilp32", "mabi=ilp32", Flags);
-  addMultilibFlag(ABIName == "ilp32f", "mabi=ilp32f", Flags);
-  addMultilibFlag(ABIName == "ilp32d", "mabi=ilp32d", Flags);
-  addMultilibFlag(ABIName == "lp64", "mabi=lp64", Flags);
-  addMultilibFlag(ABIName == "lp64f", "mabi=lp64f", Flags);
-  addMultilibFlag(ABIName == "lp64d", "mabi=lp64d", Flags);
-
-  if (RISCVMultilibs.select(Flags, Result.SelectedMultilib))
-    Result.Multilibs = RISCVMultilibs;
-}
-
 static bool findBiarchMultilibs(const Driver &D,
                                 const llvm::Triple &TargetTriple,
                                 StringRef Path, const ArgList &Args,
@@ -2389,7 +2298,10 @@
     if (!findMIPSMultilibs(D, TargetTriple, Path, Args, Detected))
       return false;
   } else if (TargetTriple.isRISCV()) {
-    findRISCVMultilibs(D, TargetTriple, Path, Args, Detected);
+    tools::riscv::findRISCVMultilibs(D, TargetTriple, Path, Args,
+                                     Detected.Multilibs,
+                                     Detected.SelectedMultilib,
+                                     /*ShouldFilterNonExistent*/true);
   } else if (isMSP430(TargetArch)) {
     findMSP430Multilibs(D, TargetTriple, Path, Args, Detected);
   } else if (TargetArch == llvm::Triple::avr) {
Index: clang/lib/Driver/ToolChains/RISCVToolchain.h
===================================================================
--- clang/lib/Driver/ToolChains/RISCVToolchain.h
+++ clang/lib/Driver/ToolChains/RISCVToolchain.h
@@ -35,6 +35,10 @@
   addLibStdCxxIncludePaths(const llvm::opt::ArgList &DriverArgs,
                            llvm::opt::ArgStringList &CC1Args) const override;
 
+  std::string getCompilerRT(const llvm::opt::ArgList &Args,
+                            StringRef Component,
+                            FileType Type) const override;
+
 protected:
   Tool *buildLinker() const override;
 
Index: clang/lib/Driver/ToolChains/RISCVToolchain.cpp
===================================================================
--- clang/lib/Driver/ToolChains/RISCVToolchain.cpp
+++ clang/lib/Driver/ToolChains/RISCVToolchain.cpp
@@ -9,11 +9,13 @@
 #include "RISCVToolchain.h"
 #include "CommonArgs.h"
 #include "InputInfo.h"
+#include "Arch/RISCV.h"
 #include "clang/Driver/Compilation.h"
 #include "clang/Driver/Options.h"
 #include "llvm/Option/ArgList.h"
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/Path.h"
+#include "llvm/Support/VirtualFileSystem.h"
 #include "llvm/Support/raw_ostream.h"
 
 using namespace clang::driver;
@@ -52,6 +54,20 @@
                          .str());
     PPaths.push_back((GCCInstallation.getParentLibPath() + "/../bin").str());
   } else {
+    riscv::findRISCVMultilibs(D, Triple, D.Dir, Args, Multilibs,
+                              SelectedMultilib,
+                              /*ShouldFilterNonExistent*/false);
+
+    // Add toolchain/multilib specific file paths.
+    path_list &FilePaths = getFilePaths();
+    addMultilibsFilePaths(D, Multilibs, SelectedMultilib, D.ResourceDir,
+                          FilePaths);
+    // Also add to the library path. This is necessary as the library paths
+    // are used when searching for compiler-rt and crtbegin/crtend.
+    path_list &LibPaths = getLibraryPaths();
+    addMultilibsFilePaths(D, Multilibs, SelectedMultilib, D.ResourceDir,
+                          LibPaths);
+
     getProgramPaths().push_back(D.Dir);
   }
   getFilePaths().push_back(computeSysRoot() + "/lib");
@@ -112,8 +128,31 @@
   } else {
     // Use the triple as provided to the driver. Unlike the parsed triple
     // this has not been normalized to always contain every field.
-    llvm::sys::path::append(SysRootDir, getDriver().Dir, "..",
-                            getDriver().getTargetTriple());
+    std::string TargetTriple = getDriver().getTargetTriple();
+
+    SmallString<32> BiarchVariantTriple;
+    SmallVector<StringRef, 2> TripleParts;
+    StringRef(TargetTriple).split(TripleParts, '-', 1);
+    if (TripleParts[0] == "riscv32") {
+      BiarchVariantTriple = "riscv64";
+    } else {
+      assert (TripleParts[0] == "riscv64");
+      BiarchVariantTriple = "riscv32";
+    }
+    if (TripleParts.size() > 1) {
+      BiarchVariantTriple += '-';
+      BiarchVariantTriple += TripleParts[1];
+    }
+
+    // First try the triple, if that doesn't exist then try the
+    // biarch variant - this matches the behaviour of the GCC install
+    // detector.
+    llvm::sys::path::append(SysRootDir, getDriver().Dir, "..", TargetTriple);
+    if (!llvm::sys::fs::exists(SysRootDir)) {
+      SysRootDir.clear();
+      llvm::sys::path::append(SysRootDir, getDriver().Dir, "..",
+                              BiarchVariantTriple);
+    }
   }
 
   if (!llvm::sys::fs::exists(SysRootDir))
@@ -122,6 +161,23 @@
   return std::string(SysRootDir.str());
 }
 
+std::string RISCVToolChain::getCompilerRT(const ArgList &Args,
+                                          StringRef Component,
+                                          FileType Type) const {
+  std::string CRTBasename =
+      getCompilerRTBasename(Args, Component, Type, /*AddArch=*/true);
+  for (const auto &LibPath : getLibraryPaths()) {
+    SmallString<128> P(LibPath);
+    llvm::sys::path::append(P, CRTBasename);
+    if (getVFS().exists(P))
+      return std::string(P.str());
+  }
+
+  SmallString<128> Path(getCompilerRTPath());
+  llvm::sys::path::append(Path, CRTBasename);
+  return std::string(Path.str());
+}
+
 void RISCV::Linker::ConstructJob(Compilation &C, const JobAction &JA,
                                  const InputInfo &Output,
                                  const InputInfoList &Inputs,
@@ -150,8 +206,8 @@
   const char *crtbegin, *crtend;
   auto RuntimeLib = ToolChain.GetRuntimeLibType(Args);
   if (RuntimeLib == ToolChain::RLT_Libgcc) {
-    crtbegin = "crtbegin.o";
-    crtend = "crtend.o";
+    crtbegin = Args.MakeArgString(ToolChain.GetFilePath("crtbegin.o"));
+    crtend = Args.MakeArgString(ToolChain.GetFilePath("crtend.o"));
   } else {
     assert (RuntimeLib == ToolChain::RLT_CompilerRT);
     crtbegin = ToolChain.getCompilerRTArgString(Args, "crtbegin",
@@ -162,7 +218,7 @@
 
   if (WantCRTs) {
     CmdArgs.push_back(Args.MakeArgString(ToolChain.GetFilePath("crt0.o")));
-    CmdArgs.push_back(Args.MakeArgString(ToolChain.GetFilePath(crtbegin)));
+    CmdArgs.push_back(crtbegin);
   }
 
   Args.AddAllArgs(CmdArgs, options::OPT_L);
@@ -187,7 +243,7 @@
   }
 
   if (WantCRTs)
-    CmdArgs.push_back(Args.MakeArgString(ToolChain.GetFilePath(crtend)));
+    CmdArgs.push_back(crtend);
 
   CmdArgs.push_back("-o");
   CmdArgs.push_back(Output.getFilename());
Index: clang/test/Driver/Inputs/multilib_riscv_elf_nogcc_tree/bin/riscv32-unknown-elf-ld
===================================================================
--- /dev/null
+++ clang/test/Driver/Inputs/multilib_riscv_elf_nogcc_tree/bin/riscv32-unknown-elf-ld
@@ -0,0 +1 @@
+#!/bin/true
Index: clang/test/Driver/Inputs/multilib_riscv_elf_nogcc_tree/bin/riscv64-unknown-elf-ld
===================================================================
--- /dev/null
+++ clang/test/Driver/Inputs/multilib_riscv_elf_nogcc_tree/bin/riscv64-unknown-elf-ld
@@ -0,0 +1 @@
+#!/bin/true
Index: clang/test/Driver/riscv32-toolchain-extra.c
===================================================================
--- clang/test/Driver/riscv32-toolchain-extra.c
+++ clang/test/Driver/riscv32-toolchain-extra.c
@@ -30,3 +30,101 @@
 // C-RV32-BAREMETAL-ILP32-NOGCC: "--start-group" "-lc" "-lgloss" "--end-group"
 // C-RV32-BAREMETAL-ILP32-NOGCC: "{{.*}}Output/testroot-riscv32-baremetal-nogcc/{{.*}}/lib/libclang_rt.builtins-riscv32.a"
 // C-RV32-BAREMETAL-ILP32-NOGCC: "{{.*}}Output/testroot-riscv32-baremetal-nogcc/{{.*}}/lib/clang_rt.crtend-riscv32.o"
+
+// Setup the directory tree for baremetal multilib with no detected GCC install
+// RUN: rm -rf %T/testroot-multilib-riscv32-elf-nogcc
+// RUN: mkdir -p %T/testroot-multilib-riscv32-elf-nogcc/bin
+// RUN: ln -s %clang %T/testroot-multilib-riscv32-elf-nogcc/bin/clang
+// RUN: ln -s %S/Inputs/multilib_riscv_elf_nogcc_tree/bin/riscv32-unknown-elf-ld %T/testroot-multilib-riscv32-elf-nogcc/bin/riscv32-unknown-elf-ld
+// RUN: ln -s %S/Inputs/multilib_riscv_elf_nogcc_tree/riscv64-unknown-elf %T/testroot-multilib-riscv32-elf-nogcc/riscv64-unknown-elf
+// RUN: ln -s %S/Inputs/multilib_riscv_elf_nogcc_tree/lib %T/testroot-multilib-riscv32-elf-nogcc/lib
+
+// RUN: %T/testroot-multilib-riscv32-elf-nogcc/bin/clang %s -### -no-canonical-prefixes \
+// RUN:   -target riscv32-unknown-elf --rtlib=platform \
+// RUN:   -march=rv32i -mabi=ilp32 \
+// RUN:   --gcc-toolchain=%T/testroot-multilib-riscv32-elf-nogcc/invalid 2>&1 \
+// RUN:   | FileCheck -check-prefix=C-RV32I-BAREMETAL-MULTI-ILP32-NOGCC %s
+
+// C-RV32I-BAREMETAL-MULTI-ILP32-NOGCC: "-internal-isystem" "{{.*}}Output/testroot-multilib-riscv32-elf-nogcc/bin/../riscv64-unknown-elf/include"
+// C-RV32I-BAREMETAL-MULTI-ILP32-NOGCC: "{{.*}}/Output/testroot-multilib-riscv32-elf-nogcc/bin/riscv32-unknown-elf-ld"
+// C-RV32I-BAREMETAL-MULTI-ILP32-NOGCC: "-m" "elf32lriscv"
+// C-RV32I-BAREMETAL-MULTI-ILP32-NOGCC: "{{.*}}/Output/testroot-multilib-riscv32-elf-nogcc/lib/clang/11.0.0/../..{{/|\\\\}}..{{/|\\\\}}riscv64-unknown-elf/lib/rv32i/ilp32{{/|\\\\}}crt0.o"
+// C-RV32I-BAREMETAL-MULTI-ILP32-NOGCC: "{{.*}}/Output/testroot-multilib-riscv32-elf-nogcc/lib/clang/11.0.0/rv32i/ilp32{{/|\\\\}}clang_rt.crtbegin-riscv32.o"
+// C-RV32I-BAREMETAL-MULTI-ILP32-NOGCC: "-L{{.*}}/Output/testroot-multilib-riscv32-elf-nogcc/lib/clang/11.0.0/rv32i/ilp32"
+// C-RV32I-BAREMETAL-MULTI-ILP32-NOGCC: "-L{{.*}}/Output/testroot-multilib-riscv32-elf-nogcc/lib/clang/11.0.0/../..{{/|\\\\}}..{{/|\\\\}}riscv64-unknown-elf/lib/rv32i/ilp32"
+// C-RV32I-BAREMETAL-MULTI-ILP32-NOGCC: "-L{{.*}}/Output/testroot-multilib-riscv32-elf-nogcc/bin/../riscv64-unknown-elf/lib"
+// C-RV32I-BAREMETAL-MULTI-ILP32-NOGCC: "--start-group" "-lc" "-lgloss" "--end-group"
+// C-RV32I-BAREMETAL-MULTI-ILP32-NOGCC: "{{.*}}/Output/testroot-multilib-riscv32-elf-nogcc/lib/clang/11.0.0/rv32i/ilp32{{/|\\\\}}libclang_rt.builtins-riscv32.a"
+// C-RV32I-BAREMETAL-MULTI-ILP32-NOGCC: "{{.*}}/Output/testroot-multilib-riscv32-elf-nogcc/lib/clang/11.0.0/rv32i/ilp32{{/|\\\\}}clang_rt.crtend-riscv32.o"
+
+// RUN: %T/testroot-multilib-riscv32-elf-nogcc/bin/clang %s -### -no-canonical-prefixes \
+// RUN:   -target riscv32-unknown-elf --rtlib=platform \
+// RUN:   -march=rv32iac -mabi=ilp32 \
+// RUN:   --gcc-toolchain=%T/testroot-multilib-riscv32-elf-nogcc/invalid 2>&1 \
+// RUN:   | FileCheck -check-prefix=C-RV32IAC-BAREMETAL-MULTI-ILP32-NOGCC %s
+
+// C-RV32IAC-BAREMETAL-MULTI-ILP32-NOGCC: "-internal-isystem" "{{.*}}Output/testroot-multilib-riscv32-elf-nogcc/bin/../riscv64-unknown-elf/include"
+// C-RV32IAC-BAREMETAL-MULTI-ILP32-NOGCC: "{{.*}}/Output/testroot-multilib-riscv32-elf-nogcc/bin/riscv32-unknown-elf-ld"
+// C-RV32IAC-BAREMETAL-MULTI-ILP32-NOGCC: "-m" "elf32lriscv"
+// C-RV32IAC-BAREMETAL-MULTI-ILP32-NOGCC: "{{.*}}/Output/testroot-multilib-riscv32-elf-nogcc/lib/clang/11.0.0/../..{{/|\\\\}}..{{/|\\\\}}riscv64-unknown-elf/lib/rv32iac/ilp32{{/|\\\\}}crt0.o"
+// C-RV32IAC-BAREMETAL-MULTI-ILP32-NOGCC: "{{.*}}/Output/testroot-multilib-riscv32-elf-nogcc/lib/clang/11.0.0/rv32iac/ilp32{{/|\\\\}}clang_rt.crtbegin-riscv32.o"
+// C-RV32IAC-BAREMETAL-MULTI-ILP32-NOGCC: "-L{{.*}}/Output/testroot-multilib-riscv32-elf-nogcc/lib/clang/11.0.0/rv32iac/ilp32"
+// C-RV32IAC-BAREMETAL-MULTI-ILP32-NOGCC: "-L{{.*}}/Output/testroot-multilib-riscv32-elf-nogcc/lib/clang/11.0.0/../..{{/|\\\\}}..{{/|\\\\}}riscv64-unknown-elf/lib/rv32iac/ilp32"
+// C-RV32IAC-BAREMETAL-MULTI-ILP32-NOGCC: "-L{{.*}}/Output/testroot-multilib-riscv32-elf-nogcc/bin/../riscv64-unknown-elf/lib"
+// C-RV32IAC-BAREMETAL-MULTI-ILP32-NOGCC: "--start-group" "-lc" "-lgloss" "--end-group"
+// C-RV32IAC-BAREMETAL-MULTI-ILP32-NOGCC: "{{.*}}/Output/testroot-multilib-riscv32-elf-nogcc/lib/clang/11.0.0/rv32iac/ilp32{{/|\\\\}}libclang_rt.builtins-riscv32.a"
+// C-RV32IAC-BAREMETAL-MULTI-ILP32-NOGCC: "{{.*}}/Output/testroot-multilib-riscv32-elf-nogcc/lib/clang/11.0.0/rv32iac/ilp32{{/|\\\\}}clang_rt.crtend-riscv32.o"
+
+// RUN: %T/testroot-multilib-riscv32-elf-nogcc/bin/clang %s -### -no-canonical-prefixes \
+// RUN:   -target riscv32-unknown-elf --rtlib=platform \
+// RUN:   -march=rv32im -mabi=ilp32 \
+// RUN:   --gcc-toolchain=%T/testroot-multilib-riscv32-elf-nogcc/invalid 2>&1 \
+// RUN:   | FileCheck -check-prefix=C-RV32IM-BAREMETAL-MULTI-ILP32-NOGCC %s
+
+// C-RV32IM-BAREMETAL-MULTI-ILP32-NOGCC: "-internal-isystem" "{{.*}}Output/testroot-multilib-riscv32-elf-nogcc/bin/../riscv64-unknown-elf/include"
+// C-RV32IM-BAREMETAL-MULTI-ILP32-NOGCC: "{{.*}}/Output/testroot-multilib-riscv32-elf-nogcc/bin/riscv32-unknown-elf-ld"
+// C-RV32IM-BAREMETAL-MULTI-ILP32-NOGCC: "-m" "elf32lriscv"
+// C-RV32IM-BAREMETAL-MULTI-ILP32-NOGCC: "{{.*}}/Output/testroot-multilib-riscv32-elf-nogcc/lib/clang/11.0.0/../..{{/|\\\\}}..{{/|\\\\}}riscv64-unknown-elf/lib/rv32im/ilp32{{/|\\\\}}crt0.o"
+// C-RV32IM-BAREMETAL-MULTI-ILP32-NOGCC: "{{.*}}/Output/testroot-multilib-riscv32-elf-nogcc/lib/clang/11.0.0/rv32im/ilp32{{/|\\\\}}clang_rt.crtbegin-riscv32.o"
+// C-RV32IM-BAREMETAL-MULTI-ILP32-NOGCC: "-L{{.*}}/Output/testroot-multilib-riscv32-elf-nogcc/lib/clang/11.0.0/rv32im/ilp32"
+// C-RV32IM-BAREMETAL-MULTI-ILP32-NOGCC: "-L{{.*}}/Output/testroot-multilib-riscv32-elf-nogcc/lib/clang/11.0.0/../..{{/|\\\\}}..{{/|\\\\}}riscv64-unknown-elf/lib/rv32im/ilp32"
+// C-RV32IM-BAREMETAL-MULTI-ILP32-NOGCC: "-L{{.*}}/Output/testroot-multilib-riscv32-elf-nogcc/bin/../riscv64-unknown-elf/lib"
+// C-RV32IM-BAREMETAL-MULTI-ILP32-NOGCC: "--start-group" "-lc" "-lgloss" "--end-group"
+// C-RV32IM-BAREMETAL-MULTI-ILP32-NOGCC: "{{.*}}/Output/testroot-multilib-riscv32-elf-nogcc/lib/clang/11.0.0/rv32im/ilp32{{/|\\\\}}libclang_rt.builtins-riscv32.a"
+// C-RV32IM-BAREMETAL-MULTI-ILP32-NOGCC: "{{.*}}/Output/testroot-multilib-riscv32-elf-nogcc/lib/clang/11.0.0/rv32im/ilp32{{/|\\\\}}clang_rt.crtend-riscv32.o"
+
+// RUN: %T/testroot-multilib-riscv32-elf-nogcc/bin/clang %s -### -no-canonical-prefixes \
+// RUN:   -target riscv32-unknown-elf --rtlib=platform \
+// RUN:   -march=rv32imac -mabi=ilp32 \
+// RUN:   --gcc-toolchain=%T/testroot-multilib-riscv32-elf-nogcc/invalid 2>&1 \
+// RUN:   | FileCheck -check-prefix=C-RV32IMAC-BAREMETAL-MULTI-ILP32-NOGCC %s
+
+// C-RV32IMAC-BAREMETAL-MULTI-ILP32-NOGCC: "-internal-isystem" "{{.*}}Output/testroot-multilib-riscv32-elf-nogcc/bin/../riscv64-unknown-elf/include"
+// C-RV32IMAC-BAREMETAL-MULTI-ILP32-NOGCC: "{{.*}}/Output/testroot-multilib-riscv32-elf-nogcc/bin/riscv32-unknown-elf-ld"
+// C-RV32IMAC-BAREMETAL-MULTI-ILP32-NOGCC: "-m" "elf32lriscv"
+// C-RV32IMAC-BAREMETAL-MULTI-ILP32-NOGCC: "{{.*}}/Output/testroot-multilib-riscv32-elf-nogcc/lib/clang/11.0.0/../..{{/|\\\\}}..{{/|\\\\}}riscv64-unknown-elf/lib/rv32imac/ilp32{{/|\\\\}}crt0.o"
+// C-RV32IMAC-BAREMETAL-MULTI-ILP32-NOGCC: "{{.*}}/Output/testroot-multilib-riscv32-elf-nogcc/lib/clang/11.0.0/rv32imac/ilp32{{/|\\\\}}clang_rt.crtbegin-riscv32.o"
+// C-RV32IMAC-BAREMETAL-MULTI-ILP32-NOGCC: "-L{{.*}}/Output/testroot-multilib-riscv32-elf-nogcc/lib/clang/11.0.0/rv32imac/ilp32"
+// C-RV32IMAC-BAREMETAL-MULTI-ILP32-NOGCC: "-L{{.*}}/Output/testroot-multilib-riscv32-elf-nogcc/lib/clang/11.0.0/../..{{/|\\\\}}..{{/|\\\\}}riscv64-unknown-elf/lib/rv32imac/ilp32"
+// C-RV32IMAC-BAREMETAL-MULTI-ILP32-NOGCC: "-L{{.*}}/Output/testroot-multilib-riscv32-elf-nogcc/bin/../riscv64-unknown-elf/lib"
+// C-RV32IMAC-BAREMETAL-MULTI-ILP32-NOGCC: "--start-group" "-lc" "-lgloss" "--end-group"
+// C-RV32IMAC-BAREMETAL-MULTI-ILP32-NOGCC: "{{.*}}/Output/testroot-multilib-riscv32-elf-nogcc/lib/clang/11.0.0/rv32imac/ilp32{{/|\\\\}}libclang_rt.builtins-riscv32.a"
+// C-RV32IMAC-BAREMETAL-MULTI-ILP32-NOGCC: "{{.*}}/Output/testroot-multilib-riscv32-elf-nogcc/lib/clang/11.0.0/rv32imac/ilp32{{/|\\\\}}clang_rt.crtend-riscv32.o"
+
+// RUN: %T/testroot-multilib-riscv32-elf-nogcc/bin/clang %s -### -no-canonical-prefixes \
+// RUN:   -target riscv32-unknown-elf --rtlib=platform \
+// RUN:   -march=rv32imafc -mabi=ilp32f \
+// RUN:   --gcc-toolchain=%T/testroot-multilib-riscv32-elf-nogcc/invalid 2>&1 \
+// RUN:   | FileCheck -check-prefix=C-RV32IMAFC-BAREMETAL-MULTI-ILP32F-NOGCC %s
+
+// C-RV32IMAFC-BAREMETAL-MULTI-ILP32F-NOGCC: "-internal-isystem" "{{.*}}Output/testroot-multilib-riscv32-elf-nogcc/bin/../riscv64-unknown-elf/include"
+// C-RV32IMAFC-BAREMETAL-MULTI-ILP32F-NOGCC: "{{.*}}/Output/testroot-multilib-riscv32-elf-nogcc/bin/riscv32-unknown-elf-ld"
+// C-RV32IMAFC-BAREMETAL-MULTI-ILP32F-NOGCC: "-m" "elf32lriscv"
+// C-RV32IMAFC-BAREMETAL-MULTI-ILP32F-NOGCC: "{{.*}}/Output/testroot-multilib-riscv32-elf-nogcc/lib/clang/11.0.0/../..{{/|\\\\}}..{{/|\\\\}}riscv64-unknown-elf/lib/rv32imafc/ilp32f{{/|\\\\}}crt0.o"
+// C-RV32IMAFC-BAREMETAL-MULTI-ILP32F-NOGCC: "{{.*}}/Output/testroot-multilib-riscv32-elf-nogcc/lib/clang/11.0.0/rv32imafc/ilp32f{{/|\\\\}}clang_rt.crtbegin-riscv32.o"
+// C-RV32IMAFC-BAREMETAL-MULTI-ILP32F-NOGCC: "-L{{.*}}/Output/testroot-multilib-riscv32-elf-nogcc/lib/clang/11.0.0/rv32imafc/ilp32f"
+// C-RV32IMAFC-BAREMETAL-MULTI-ILP32F-NOGCC: "-L{{.*}}/Output/testroot-multilib-riscv32-elf-nogcc/lib/clang/11.0.0/../..{{/|\\\\}}..{{/|\\\\}}riscv64-unknown-elf/lib/rv32imafc/ilp32f"
+// C-RV32IMAFC-BAREMETAL-MULTI-ILP32F-NOGCC: "-L{{.*}}/Output/testroot-multilib-riscv32-elf-nogcc/bin/../riscv64-unknown-elf/lib"
+// C-RV32IMAFC-BAREMETAL-MULTI-ILP32F-NOGCC: "--start-group" "-lc" "-lgloss" "--end-group"
+// C-RV32IMAFC-BAREMETAL-MULTI-ILP32F-NOGCC: "{{.*}}/Output/testroot-multilib-riscv32-elf-nogcc/lib/clang/11.0.0/rv32imafc/ilp32f{{/|\\\\}}libclang_rt.builtins-riscv32.a"
+// C-RV32IMAFC-BAREMETAL-MULTI-ILP32F-NOGCC: "{{.*}}/Output/testroot-multilib-riscv32-elf-nogcc/lib/clang/11.0.0/rv32imafc/ilp32f{{/|\\\\}}clang_rt.crtend-riscv32.o"
Index: clang/test/Driver/riscv64-toolchain-extra.c
===================================================================
--- clang/test/Driver/riscv64-toolchain-extra.c
+++ clang/test/Driver/riscv64-toolchain-extra.c
@@ -30,3 +30,47 @@
 // C-RV64-BAREMETAL-LP64-NOGCC: "--start-group" "-lc" "-lgloss" "--end-group"
 // C-RV64-BAREMETAL-LP64-NOGCC: "{{.*}}Output/testroot-riscv64-baremetal-nogcc/{{.*}}/lib/libclang_rt.builtins-riscv64.a"
 // C-RV64-BAREMETAL-LP64-NOGCC: "{{.*}}Output/testroot-riscv64-baremetal-nogcc/{{.*}}/lib/clang_rt.crtend-riscv64.o"
+
+// Setup the directory tree for baremetal multilib with no detected GCC install
+// RUN: rm -rf %T/testroot-multilib-riscv64-elf-nogcc
+// RUN: mkdir -p %T/testroot-multilib-riscv64-elf-nogcc/bin
+// RUN: ln -s %clang %T/testroot-multilib-riscv64-elf-nogcc/bin/clang
+// RUN: ln -s %S/Inputs/multilib_riscv_elf_nogcc_tree/bin/riscv64-unknown-elf-ld %T/testroot-multilib-riscv64-elf-nogcc/bin/riscv64-unknown-elf-ld
+// RUN: ln -s %S/Inputs/multilib_riscv_elf_nogcc_tree/riscv64-unknown-elf %T/testroot-multilib-riscv64-elf-nogcc/riscv64-unknown-elf
+// RUN: ln -s %S/Inputs/multilib_riscv_elf_nogcc_tree/lib %T/testroot-multilib-riscv64-elf-nogcc/lib
+
+// RUN: %T/testroot-multilib-riscv64-elf-nogcc/bin/clang %s -### -no-canonical-prefixes \
+// RUN:   -target riscv64-unknown-elf --rtlib=platform \
+// RUN:   -march=rv64imac -mabi=lp64 \
+// RUN:   --gcc-toolchain=%T/testroot-multilib-riscv64-elf-nogcc/invalid 2>&1 \
+// RUN:   | FileCheck -check-prefix=C-RV64IMAC-BAREMETAL-MULTI-LP64-NOGCC %s
+
+// C-RV64IMAC-BAREMETAL-MULTI-LP64-NOGCC: "-internal-isystem" "{{.*}}Output/testroot-multilib-riscv64-elf-nogcc/bin/../riscv64-unknown-elf/include"
+// C-RV64IMAC-BAREMETAL-MULTI-LP64-NOGCC: "{{.*}}/Output/testroot-multilib-riscv64-elf-nogcc/bin/riscv64-unknown-elf-ld"
+// C-RV64IMAC-BAREMETAL-MULTI-LP64-NOGCC: "-m" "elf64lriscv"
+// C-RV64IMAC-BAREMETAL-MULTI-LP64-NOGCC: "{{.*}}/Output/testroot-multilib-riscv64-elf-nogcc/lib/clang/11.0.0/../..{{/|\\\\}}..{{/|\\\\}}riscv64-unknown-elf/lib/rv64imac/lp64{{/|\\\\}}crt0.o"
+// C-RV64IMAC-BAREMETAL-MULTI-LP64-NOGCC: "{{.*}}/Output/testroot-multilib-riscv64-elf-nogcc/lib/clang/11.0.0/rv64imac/lp64{{/|\\\\}}clang_rt.crtbegin-riscv64.o"
+// C-RV64IMAC-BAREMETAL-MULTI-LP64-NOGCC: "-L{{.*}}/Output/testroot-multilib-riscv64-elf-nogcc/lib/clang/11.0.0/rv64imac/lp64"
+// C-RV64IMAC-BAREMETAL-MULTI-LP64-NOGCC: "-L{{.*}}/Output/testroot-multilib-riscv64-elf-nogcc/lib/clang/11.0.0/../..{{/|\\\\}}..{{/|\\\\}}riscv64-unknown-elf/lib/rv64imac/lp64"
+// C-RV64IMAC-BAREMETAL-MULTI-LP64-NOGCC: "-L{{.*}}/Output/testroot-multilib-riscv64-elf-nogcc/bin/../riscv64-unknown-elf/lib"
+// C-RV64IMAC-BAREMETAL-MULTI-LP64-NOGCC: "--start-group" "-lc" "-lgloss" "--end-group"
+// C-RV64IMAC-BAREMETAL-MULTI-LP64-NOGCC: "{{.*}}/Output/testroot-multilib-riscv64-elf-nogcc/lib/clang/11.0.0/rv64imac/lp64{{/|\\\\}}libclang_rt.builtins-riscv64.a"
+// C-RV64IMAC-BAREMETAL-MULTI-LP64-NOGCC: "{{.*}}/Output/testroot-multilib-riscv64-elf-nogcc/lib/clang/11.0.0/rv64imac/lp64{{/|\\\\}}clang_rt.crtend-riscv64.o"
+
+// RUN: %T/testroot-multilib-riscv64-elf-nogcc/bin/clang %s -### -no-canonical-prefixes \
+// RUN:   -target riscv64-unknown-elf --rtlib=platform \
+// RUN:   -march=rv64imafdc -mabi=lp64d \
+// RUN:   --gcc-toolchain=%T/testroot-multilib-riscv64-elf-nogcc/invalid 2>&1 \
+// RUN:   | FileCheck -check-prefix=C-RV64IMAFDC-BAREMETAL-MULTI-LP64D-NOGCC %s
+
+// C-RV64IMAFDC-BAREMETAL-MULTI-LP64D-NOGCC: "-internal-isystem" "{{.*}}Output/testroot-multilib-riscv64-elf-nogcc/bin/../riscv64-unknown-elf/include"
+// C-RV64IMAFDC-BAREMETAL-MULTI-LP64D-NOGCC: "{{.*}}/Output/testroot-multilib-riscv64-elf-nogcc/bin/riscv64-unknown-elf-ld"
+// C-RV64IMAFDC-BAREMETAL-MULTI-LP64D-NOGCC: "-m" "elf64lriscv"
+// C-RV64IMAFDC-BAREMETAL-MULTI-LP64D-NOGCC: "{{.*}}/Output/testroot-multilib-riscv64-elf-nogcc/lib/clang/11.0.0/../..{{/|\\\\}}..{{/|\\\\}}riscv64-unknown-elf/lib/rv64imafdc/lp64d{{/|\\\\}}crt0.o"
+// C-RV64IMAFDC-BAREMETAL-MULTI-LP64D-NOGCC: "{{.*}}/Output/testroot-multilib-riscv64-elf-nogcc/lib/clang/11.0.0/rv64imafdc/lp64d{{/|\\\\}}clang_rt.crtbegin-riscv64.o"
+// C-RV64IMAFDC-BAREMETAL-MULTI-LP64D-NOGCC: "-L{{.*}}/Output/testroot-multilib-riscv64-elf-nogcc/lib/clang/11.0.0/rv64imafdc/lp64d"
+// C-RV64IMAFDC-BAREMETAL-MULTI-LP64D-NOGCC: "-L{{.*}}/Output/testroot-multilib-riscv64-elf-nogcc/lib/clang/11.0.0/../..{{/|\\\\}}..{{/|\\\\}}riscv64-unknown-elf/lib/rv64imafdc/lp64d"
+// C-RV64IMAFDC-BAREMETAL-MULTI-LP64D-NOGCC: "-L{{.*}}/Output/testroot-multilib-riscv64-elf-nogcc/bin/../riscv64-unknown-elf/lib"
+// C-RV64IMAFDC-BAREMETAL-MULTI-LP64D-NOGCC: "--start-group" "-lc" "-lgloss" "--end-group"
+// C-RV64IMAFDC-BAREMETAL-MULTI-LP64D-NOGCC: "{{.*}}/Output/testroot-multilib-riscv64-elf-nogcc/lib/clang/11.0.0/rv64imafdc/lp64d{{/|\\\\}}libclang_rt.builtins-riscv64.a"
+// C-RV64IMAFDC-BAREMETAL-MULTI-LP64D-NOGCC: "{{.*}}/Output/testroot-multilib-riscv64-elf-nogcc/lib/clang/11.0.0/rv64imafdc/lp64d{{/|\\\\}}clang_rt.crtend-riscv64.o"