[clang][ARM] Enable --print-supported-extensions for ARM (#66083)

```
$ ./bin/clang --target=arm-linux-gnueabihf --print-supported-extensions
<...>
All available -march extensions for ARM

        crc
        crypto
        sha2
        aes
        dotprod
<...>
```

This follows the format set by RISC-V and AArch64. As for AArch64, ARM
doesn't have versioned extensions like RISC-V does. So there is only 1
column, which contains the name.

Any extension without a "feature" is hidden as these cannot be used with
-march.

clang/include/clang/Driver/Options.td

@@ -5271,7 +5271,7 @@ def print_supported_cpus : Flag<["-", "--"], "print-supported-cpus">,
   MarshallingInfoFlag<FrontendOpts<"PrintSupportedCPUs">>;
 def print_supported_extensions : Flag<["-", "--"], "print-supported-extensions">,
   Visibility<[ClangOption, CC1Option, CLOption]>,
-  HelpText<"Print supported -march extensions (RISC-V and AArch64 only)">,
+  HelpText<"Print supported -march extensions (RISC-V, AArch64 and ARM only)">,
   MarshallingInfoFlag<FrontendOpts<"PrintSupportedExtensions">>;
 def : Flag<["-"], "mcpu=help">, Alias<print_supported_cpus>;
 def : Flag<["-"], "mtune=help">, Alias<print_supported_cpus>;

clang/lib/Driver/Driver.cpp

@@ -4285,7 +4285,8 @@ void Driver::BuildActions(Compilation &C, DerivedArgList &Args,
     if (Arg *A = Args.getLastArg(Opt)) {
       if (Opt == options::OPT_print_supported_extensions &&
           !C.getDefaultToolChain().getTriple().isRISCV() &&
-          !C.getDefaultToolChain().getTriple().isAArch64()) {
+          !C.getDefaultToolChain().getTriple().isAArch64() &&
+          !C.getDefaultToolChain().getTriple().isARM()) {
         C.getDriver().Diag(diag::err_opt_not_valid_on_target)
             << "--print-supported-extensions";
         return;

clang/test/Driver/print-supported-extensions.c

@@ -9,6 +9,10 @@
 // RUN:   --print-supported-extensions 2>&1 | FileCheck %s --check-prefix RISCV %}
 // RISCV: All available -march extensions for RISC-V
 
+// RUN: %if arm-registered-target %{ %clang --target=arm-linux-gnu \
+// RUN:   --print-supported-extensions 2>&1 | FileCheck %s --check-prefix ARM %}
+// ARM: All available -march extensions for ARM
+
 // RUN: %if x86-registered-target %{ not %clang --target=x86_64-linux-gnu \
 // RUN:   --print-supported-extensions 2>&1 | FileCheck %s --check-prefix X86 %}
 // X86: error: option '--print-supported-extensions' cannot be specified on this target

clang/tools/driver/cc1_main.cpp

@@ -46,6 +46,7 @@
 #include "llvm/Support/raw_ostream.h"
 #include "llvm/Target/TargetMachine.h"
 #include "llvm/TargetParser/AArch64TargetParser.h"
+#include "llvm/TargetParser/ARMTargetParser.h"
 #include <cstdio>
 
 #ifdef CLANG_HAVE_RLIMITS
@@ -202,6 +203,8 @@ static int PrintSupportedExtensions(std::string TargetStr) {
     llvm::riscvExtensionsHelp();
   else if (MachineTriple.isAArch64())
     llvm::AArch64::PrintSupportedExtensions();
+  else if (MachineTriple.isARM())
+    llvm::ARM::PrintSupportedExtensions();
   else {
     // The option was already checked in Driver::HandleImmediateArgs,
     // so we do not expect to get here if we are not a supported architecture.

llvm/include/llvm/TargetParser/ARMTargetParser.h

@@ -259,6 +259,8 @@ StringRef computeDefaultTargetABI(const Triple &TT, StringRef CPU);
 /// string then the triple's arch name is used.
 StringRef getARMCPUForArch(const llvm::Triple &Triple, StringRef MArch = {});
 
+void PrintSupportedExtensions();
+
 } // namespace ARM
 } // namespace llvm
 

llvm/lib/TargetParser/ARMTargetParser.cpp

@@ -13,6 +13,7 @@
 
 #include "llvm/TargetParser/ARMTargetParser.h"
 #include "llvm/ADT/StringSwitch.h"
+#include "llvm/Support/raw_ostream.h"
 #include "llvm/TargetParser/ARMTargetParserCommon.h"
 #include "llvm/TargetParser/Triple.h"
 #include <cctype>
@@ -598,3 +599,12 @@ StringRef ARM::getARMCPUForArch(const llvm::Triple &Triple, StringRef MArch) {
 
   llvm_unreachable("invalid arch name");
 }
+
+void ARM::PrintSupportedExtensions() {
+  outs() << "All available -march extensions for ARM\n\n";
+  for (const auto &Ext : ARCHExtNames) {
+    // Extensions without a feature cannot be used with -march.
+    if (!Ext.Feature.empty())
+      outs() << '\t' << Ext.Name << "\n";
+  }
+}

llvm/unittests/TargetParser/TargetParserTest.cpp

@@ -1010,6 +1010,29 @@ TEST(TargetParserTest, getARMCPUForArch) {
   }
 }
 
+TEST(TargetParserTest, ARMPrintSupportedExtensions) {
+  std::string expected = "All available -march extensions for ARM\n\n"
+                         "\tcrc\n\tcrypto\n\tsha2";
+
+  outs().flush();
+  testing::internal::CaptureStdout();
+  ARM::PrintSupportedExtensions();
+  outs().flush();
+  std::string captured = testing::internal::GetCapturedStdout();
+
+  // Check that the start of the output is as expected.
+  EXPECT_EQ(0ULL, captured.find(expected));
+
+  // Should not include "none" or "invalid".
+  EXPECT_EQ(std::string::npos, captured.find("none"));
+  EXPECT_EQ(std::string::npos, captured.find("invalid"));
+  // Should not include anything that lacks a feature name. Checking a few here
+  // but not all as if one is hidden correctly the rest should be.
+  EXPECT_EQ(std::string::npos, captured.find("simd"));
+  EXPECT_EQ(std::string::npos, captured.find("maverick"));
+  EXPECT_EQ(std::string::npos, captured.find("xscale"));
+}
+
 class AArch64CPUTestFixture
     : public ::testing::TestWithParam<
           ARMCPUTestParams<AArch64::ExtensionBitset>> {};