[Clang][LoongArch] Pass "f" and "d" features to cc1 to enable hard float

On LoongArch, currently neither of "f" and "d" feature is passed from
clang driver to cc1 by default. This means the backend generates code
for soft float.

In order to run programs in current LoongArch machines (hard float
environment) this patch temporarily enables "f" and "d" features.

In future, we should conditionally turn on these features depend on
various clang options, e.g. -mdouble-float, -msingle-float,
-msoft-float and -mfpu.

clang/lib/Driver/ToolChains/Arch/LoongArch.cpp

@@ -26,3 +26,14 @@ StringRef loongarch::getLoongArchABI(const ArgList &Args,
   // TODO: select appropiate ABI.
   return Triple.getArch() == llvm::Triple::loongarch32 ? "ilp32d" : "lp64d";
 }
+
+void loongarch::getLoongArchTargetFeatures(const Driver &D,
+                                           const llvm::Triple &Triple,
+                                           const ArgList &Args,
+                                           std::vector<StringRef> &Features) {
+  // FIXME: hornor various clang options that may affect target features, e.g.
+  // -march/-mtune/-mdouble-float/-msingle-float/-msoft-float/-mfpu. See:
+  // https://loongson.github.io/LoongArch-Documentation/LoongArch-toolchain-conventions-EN.html
+  Features.push_back("+f");
+  Features.push_back("+d");
+}

clang/lib/Driver/ToolChains/Arch/LoongArch.h

@@ -19,6 +19,10 @@ namespace tools {
 namespace loongarch {
 StringRef getLoongArchABI(const llvm::opt::ArgList &Args,
                           const llvm::Triple &Triple);
+
+void getLoongArchTargetFeatures(const Driver &D, const llvm::Triple &Triple,
+                                const llvm::opt::ArgList &Args,
+                                std::vector<llvm::StringRef> &Features);
 } // end namespace loongarch
 } // end namespace tools
 } // end namespace driver

clang/lib/Driver/ToolChains/Clang.cpp

@@ -372,6 +372,10 @@ static void getTargetFeatures(const Driver &D, const llvm::Triple &Triple,
   case llvm::Triple::csky:
     csky::getCSKYTargetFeatures(D, Triple, Args, CmdArgs, Features);
     break;
+  case llvm::Triple::loongarch32:
+  case llvm::Triple::loongarch64:
+    loongarch::getLoongArchTargetFeatures(D, Triple, Args, Features);
+    break;
   }
 
   for (auto Feature : unifyTargetFeatures(Features)) {

clang/test/Driver/loongarch-default-features.c

@@ -0,0 +1,10 @@
+// RUN: %clang --target=loongarch32 -S -emit-llvm %s -o - | FileCheck %s --check-prefix=LA32
+// RUN: %clang --target=loongarch64 -S -emit-llvm %s -o - | FileCheck %s --check-prefix=LA64
+
+// LA32: "target-features"="+d,+f"
+// LA64: "target-features"="+d,+f"
+
+/// Dummy function
+int foo(void) {
+  return  3;
+}