[RISCV] Remove duplicated logic when determining the target ABI

We were calculating twice ilp32/lp64. Do this in one place instead.

Differential Revision: https://reviews.llvm.org/D48357

llvm-svn: 368128
diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
index bac6cff..ed557a6 100644
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -1848,21 +1848,11 @@
 
 void Clang::AddRISCVTargetArgs(const ArgList &Args,
                                ArgStringList &CmdArgs) const {
-  // FIXME: currently defaults to the soft-float ABIs. Will need to be
-  // expanded to select ilp32f, ilp32d, lp64f, lp64d when appropriate.
-  const char *ABIName = nullptr;
   const llvm::Triple &Triple = getToolChain().getTriple();
-  if (Arg *A = Args.getLastArg(options::OPT_mabi_EQ))
-    ABIName = A->getValue();
-  else if (Triple.getArch() == llvm::Triple::riscv32)
-    ABIName = "ilp32";
-  else if (Triple.getArch() == llvm::Triple::riscv64)
-    ABIName = "lp64";
-  else
-    llvm_unreachable("Unexpected triple!");
+  StringRef ABIName = riscv::getRISCVABI(Args, Triple);
 
   CmdArgs.push_back("-target-abi");
-  CmdArgs.push_back(ABIName);
+  CmdArgs.push_back(ABIName.data());
 }
 
 void Clang::AddSparcTargetArgs(const ArgList &Args,