[RISCV] Print a better error message when a rv32 CPU is used on rv64 and vice versa.

[craig.topper]

Summary

Instead of rejecting the CPU out right with no information, try
to diagnose that it doesn't match the triple.

[craig.topper]

Upload the whole patch

[asb]

LGTM.

clang/include/clang/Basic/DiagnosticDriverKinds.td

def err_drv_unknown_stdin_type : Error<
   "-E or -x required when input is from standard input">;
 def err_drv_unknown_stdin_type_clang_cl : Error<
   "use /Tc or /Tp to set input type for standard input">;
 def err_drv_unknown_language : Error<"language not recognized: '%0'">;
 def err_drv_invalid_arch_name : Error<
   "invalid arch name '%0'">;
 def err_drv_invalid_riscv_arch_name : Error<
   "invalid arch name '%0', %1">;
+def err_drv_invalid_riscv_cpu_name_for_target : Error<
+  "cpu '%0' does not support rv%select{32|64}1">;
 def warn_drv_invalid_arch_name_with_suggestion : Warning<
   "ignoring invalid /arch: argument '%0'; for %select{64|32}1-bit expected one of %2">,
   InGroup<UnusedCommandLineArgument>;
 def warn_drv_avr_mcu_not_specified : Warning<
   "no target microcontroller specified on command line, cannot "
   "link standard libraries, please pass -mmcu=<mcu name>">,
   InGroup<AVRRtlibLinkingQuirks>;
 def warn_drv_avr_libc_not_found: Warning<

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

static bool getArchFeatures(const Driver &D, StringRef Arch,
 
   (*ISAInfo)->toFeatures(
       Features, [&Args](const Twine &Str) { return Args.MakeArgString(Str); },
       /*AddAllExtensions=*/true);
   return true;
 }
 
 // Get features except standard extension feature
-static bool getRISCFeaturesFromMcpu(const llvm::Triple &Triple, StringRef Mcpu,
+static void getRISCFeaturesFromMcpu(const Driver &D, const Arg *A,
+                                    const llvm::Triple &Triple,
+                                    StringRef Mcpu,
                                     std::vector<StringRef> &Features) {
   bool Is64Bit = Triple.isRISCV64();
   llvm::RISCV::CPUKind CPUKind = llvm::RISCV::parseCPUKind(Mcpu);
-  return llvm::RISCV::checkCPUKind(CPUKind, Is64Bit);
+  if (!llvm::RISCV::checkCPUKind(CPUKind, Is64Bit)) {
+    // Try inverting Is64Bit in case the CPU is valid, but for the wrong target.
+    if (llvm::RISCV::checkCPUKind(CPUKind, !Is64Bit))
+      D.Diag(clang::diag::err_drv_invalid_riscv_cpu_name_for_target) << Mcpu << Is64Bit;
+    else
+      D.Diag(clang::diag::err_drv_unsupported_option_argument)
+          << A->getSpelling() << Mcpu;
+  }
 }
 
 void riscv::getRISCVTargetFeatures(const Driver &D, const llvm::Triple &Triple,
                                    const ArgList &Args,
                                    std::vector<StringRef> &Features) {
   StringRef MArch = getRISCVArch(Args, Triple);
 
   if (!getArchFeatures(D, MArch, Features, Args))
     return;
 
   // If users give march and mcpu, get std extension feature from MArch
   // and other features (ex. mirco architecture feature) from mcpu
   if (Arg *A = Args.getLastArg(options::OPT_mcpu_EQ)) {
     StringRef CPU = A->getValue();
     if (CPU == "native")
       CPU = llvm::sys::getHostCPUName();
-    if (!getRISCFeaturesFromMcpu(Triple, CPU, Features))
-      D.Diag(clang::diag::err_drv_unsupported_option_argument)
-          << A->getSpelling() << CPU;
+
+    getRISCFeaturesFromMcpu(D, A, Triple, CPU, Features);
   }
 
   // Handle features corresponding to "-ffixed-X" options
   if (Args.hasArg(options::OPT_ffixed_x1))
     Features.push_back("+reserve-x1");
   if (Args.hasArg(options::OPT_ffixed_x2))
     Features.push_back("+reserve-x2");
   if (Args.hasArg(options::OPT_ffixed_x3))

clang/test/Driver/riscv-cpus.c

 // MTUNE-E31-MCPU-E76-SAME: "-tune-cpu" "sifive-e76"
 
 // Check failed cases
 
 // RUN: %clang --target=riscv32 -### -c %s 2>&1 -mcpu=generic-rv321 | FileCheck -check-prefix=FAIL-MCPU-NAME %s
 // FAIL-MCPU-NAME: error: unsupported argument 'generic-rv321' to option '-mcpu='
 
 // RUN: %clang --target=riscv32 -### -c %s 2>&1 -mcpu=generic-rv32 -march=rv64i | FileCheck -check-prefix=MISMATCH-ARCH %s
-// MISMATCH-ARCH: error: unsupported argument 'generic-rv32' to option '-mcpu='
+// MISMATCH-ARCH: cpu 'generic-rv32' does not support rv64
 
 // RUN: %clang --target=riscv32 -### -c %s 2>&1 -mcpu=generic-rv64 | FileCheck -check-prefix=MISMATCH-MCPU %s
-// MISMATCH-MCPU: error: unsupported argument 'generic-rv64' to option '-mcpu='
+// MISMATCH-MCPU: error: cpu 'generic-rv64' does not support rv32