[RISCV] Use compiler-rt if no GCC installation detected

If a GCC installation is not detected, then this attempts to
use compiler-rt and the compiler-rt crtbegin/crtend
implementations as a fallback.

Differential Revision: https://reviews.llvm.org/D68407

Author: edward-jones

clang/lib/Driver/ToolChains/RISCVToolchain.cpp

@@ -41,6 +41,16 @@ Tool *RISCVToolChain::buildLinker() const {
   return new tools::RISCV::Linker(*this);
 }
 
+ToolChain::RuntimeLibType RISCVToolChain::GetDefaultRuntimeLibType() const {
+  return GCCInstallation.isValid() ?
+    ToolChain::RLT_Libgcc : ToolChain::RLT_CompilerRT;
+}
+
+ToolChain::UnwindLibType
+RISCVToolChain::GetUnwindLibType(const llvm::opt::ArgList &Args) const {
+  return ToolChain::UNW_None;
+}
+
 void RISCVToolChain::addClangTargetOptions(
     const llvm::opt::ArgList &DriverArgs,
     llvm::opt::ArgStringList &CC1Args,
@@ -110,9 +120,22 @@ void RISCV::Linker::ConstructJob(Compilation &C, const JobAction &JA,
   bool WantCRTs =
       !Args.hasArg(options::OPT_nostdlib, options::OPT_nostartfiles);
 
+  const char *crtbegin, *crtend;
+  auto RuntimeLib = ToolChain.GetRuntimeLibType(Args);
+  if (RuntimeLib == ToolChain::RLT_Libgcc) {
+    crtbegin = "crtbegin.o";
+    crtend = "crtend.o";
+  } else {
+    assert (RuntimeLib == ToolChain::RLT_CompilerRT);
+    crtbegin = ToolChain.getCompilerRTArgString(Args, "crtbegin",
+                                                ToolChain::FT_Object);
+    crtend = ToolChain.getCompilerRTArgString(Args, "crtend",
+                                              ToolChain::FT_Object);
+  }
+
   if (WantCRTs) {
     CmdArgs.push_back(Args.MakeArgString(ToolChain.GetFilePath("crt0.o")));
-    CmdArgs.push_back(Args.MakeArgString(ToolChain.GetFilePath("crtbegin.o")));
+    CmdArgs.push_back(Args.MakeArgString(ToolChain.GetFilePath(crtbegin)));
   }
 
   Args.AddAllArgs(CmdArgs, options::OPT_L);
@@ -133,11 +156,11 @@ void RISCV::Linker::ConstructJob(Compilation &C, const JobAction &JA,
     CmdArgs.push_back("-lc");
     CmdArgs.push_back("-lgloss");
     CmdArgs.push_back("--end-group");
-    CmdArgs.push_back("-lgcc");
+    AddRunTimeLibs(ToolChain, ToolChain.getDriver(), CmdArgs, Args);
   }
 
   if (WantCRTs)
-    CmdArgs.push_back(Args.MakeArgString(ToolChain.GetFilePath("crtend.o")));
+    CmdArgs.push_back(Args.MakeArgString(ToolChain.GetFilePath(crtend)));
 
   CmdArgs.push_back("-o");
   CmdArgs.push_back(Output.getFilename());

clang/lib/Driver/ToolChains/RISCVToolchain.h

@@ -25,6 +25,9 @@ class LLVM_LIBRARY_VISIBILITY RISCVToolChain : public Generic_ELF {
   void addClangTargetOptions(const llvm::opt::ArgList &DriverArgs,
                              llvm::opt::ArgStringList &CC1Args,
                              Action::OffloadKind) const override;
+  RuntimeLibType GetDefaultRuntimeLibType() const override;
+  UnwindLibType
+  GetUnwindLibType(const llvm::opt::ArgList &Args) const override;
   void
   AddClangSystemIncludeArgs(const llvm::opt::ArgList &DriverArgs,
                             llvm::opt::ArgStringList &CC1Args) const override;

clang/test/Driver/Inputs/basic_riscv32_nogcc_tree/riscv32-unknown-elf/lib/crtbegin.o

@@ -22,12 +22,12 @@
 // RUN:    -target riscv32-unknown-elf 2>&1 \
 // RUN:    | FileCheck -check-prefix=C-RV32-BAREMETAL-ILP32-NOGCC %s
 
-// C-RV32-BAREMETAL-ILP32-NOGCC: InstalledDir: [[DRIVERDIR:.*]]
 // C-RV32-BAREMETAL-ILP32-NOGCC: "-fuse-init-array"
-// C-RV32-BAREMETAL-ILP32-NOGCC: "-internal-isystem" "[[DRIVERDIR]]/../riscv32-unknown-elf/include"
-// C-RV32-BAREMETAL-ILP32-NOGCC: "[[DRIVERDIR]]/riscv32-unknown-elf-ld"
-// C-RV32-BAREMETAL-ILP32-NOGCC: "[[DRIVERDIR]]/../riscv32-unknown-elf/lib/crt0.o"
-// C-RV32-BAREMETAL-ILP32-NOGCC: "[[DRIVERDIR]]/../riscv32-unknown-elf/lib/crtbegin.o"
-// C-RV32-BAREMETAL-ILP32-NOGCC: "-L[[DRIVERDIR]]/../riscv32-unknown-elf/lib"
-// C-RV32-BAREMETAL-ILP32-NOGCC: "--start-group" "-lc" "-lgloss" "--end-group" "-lgcc"
-// C-RV32-BAREMETAL-ILP32-NOGCC: "[[DRIVERDIR]]/../riscv32-unknown-elf/lib/crtend.o"
+// C-RV32-BAREMETAL-ILP32-NOGCC: "-internal-isystem" "{{.*}}Output/testroot-riscv32-baremetal-nogcc/bin/../riscv32-unknown-elf/include"
+// C-RV32-BAREMETAL-ILP32-NOGCC: "{{.*}}Output/testroot-riscv32-baremetal-nogcc/bin/riscv32-unknown-elf-ld"
+// C-RV32-BAREMETAL-ILP32-NOGCC: "{{.*}}Output/testroot-riscv32-baremetal-nogcc/bin/../riscv32-unknown-elf/lib/crt0.o"
+// C-RV32-BAREMETAL-ILP32-NOGCC: "{{.*}}Output/testroot-riscv32-baremetal-nogcc/lib/clang/{{[0-9.]*}}/lib/clang_rt.crtbegin-riscv32.o"
+// C-RV32-BAREMETAL-ILP32-NOGCC: "{{.*}}Output/testroot-riscv32-baremetal-nogcc/bin/../riscv32-unknown-elf/lib"
+// C-RV32-BAREMETAL-ILP32-NOGCC: "--start-group" "-lc" "-lgloss" "--end-group"
+// C-RV32-BAREMETAL-ILP32-NOGCC: "{{.*}}Output/testroot-riscv32-baremetal-nogcc/lib/clang/{{[0-9.]*}}/lib/libclang_rt.builtins-riscv32.a"
+// C-RV32-BAREMETAL-ILP32-NOGCC: "{{.*}}Output/testroot-riscv32-baremetal-nogcc/lib/clang/{{[0-9.]*}}/lib/clang_rt.crtend-riscv32.o"

clang/test/Driver/Inputs/basic_riscv32_nogcc_tree/riscv32-unknown-elf/lib/crtend.o

@@ -22,12 +22,12 @@
 // RUN:    -target riscv64-unknown-elf 2>&1 \
 // RUN:    | FileCheck -check-prefix=C-RV64-BAREMETAL-LP64-NOGCC %s
 
-// C-RV64-BAREMETAL-LP64-NOGCC: InstalledDir: [[DRIVERDIR:.*]]
 // C-RV64-BAREMETAL-LP64-NOGCC: "-fuse-init-array"
-// C-RV64-BAREMETAL-LP64-NOGCC: "-internal-isystem" "[[DRIVERDIR]]/../riscv64-unknown-elf/include"
-// C-RV64-BAREMETAL-LP64-NOGCC: "[[DRIVERDIR]]/riscv64-unknown-elf-ld"
-// C-RV64-BAREMETAL-LP64-NOGCC: "[[DRIVERDIR]]/../riscv64-unknown-elf/lib/crt0.o"
-// C-RV64-BAREMETAL-LP64-NOGCC: "[[DRIVERDIR]]/../riscv64-unknown-elf/lib/crtbegin.o"
-// C-RV64-BAREMETAL-LP64-NOGCC: "-L[[DRIVERDIR]]/../riscv64-unknown-elf/lib"
-// C-RV64-BAREMETAL-LP64-NOGCC: "--start-group" "-lc" "-lgloss" "--end-group" "-lgcc"
-// C-RV64-BAREMETAL-LP64-NOGCC: "[[DRIVERDIR]]/../riscv64-unknown-elf/lib/crtend.o"
+// C-RV64-BAREMETAL-LP64-NOGCC: "-internal-isystem" "{{.*}}Output/testroot-riscv64-baremetal-nogcc/bin/../riscv64-unknown-elf/include"
+// C-RV64-BAREMETAL-LP64-NOGCC: "{{.*}}Output/testroot-riscv64-baremetal-nogcc/bin/riscv64-unknown-elf-ld"
+// C-RV64-BAREMETAL-LP64-NOGCC: "{{.*}}Output/testroot-riscv64-baremetal-nogcc/bin/../riscv64-unknown-elf/lib/crt0.o"
+// C-RV64-BAREMETAL-LP64-NOGCC: "{{.*}}Output/testroot-riscv64-baremetal-nogcc/lib/clang/{{[0-9.]*}}/lib/clang_rt.crtbegin-riscv64.o"
+// C-RV64-BAREMETAL-LP64-NOGCC: "{{.*}}Output/testroot-riscv64-baremetal-nogcc/bin/../riscv64-unknown-elf/lib"
+// C-RV64-BAREMETAL-LP64-NOGCC: "--start-group" "-lc" "-lgloss" "--end-group"
+// C-RV64-BAREMETAL-LP64-NOGCC: "{{.*}}Output/testroot-riscv64-baremetal-nogcc/lib/clang/{{[0-9.]*}}/lib/libclang_rt.builtins-riscv64.a"
+// C-RV64-BAREMETAL-LP64-NOGCC: "{{.*}}Output/testroot-riscv64-baremetal-nogcc/lib/clang/{{[0-9.]*}}/lib/clang_rt.crtend-riscv64.o"