[llvm] [llvm-objdump] Add triple support to `mcpu=help` (PR #165661)

[Ruoyu Qiu via llvm-commits]

https://github.com/cabbaken created https://github.com/llvm/llvm-project/pull/165661

Current `--mcpu=help` needs `-d` to work.
I specialise `--mcpu=help`, you can just use `--mcpu=help --triple ` without specify `-d` now.

Fixes: #150567

>From 9f37b38971c60fb2ab0f0f9b8005555f44007c9f Mon Sep 17 00:00:00 2001
From: Ruoyu Qiu <cabbaken at outlook.com>
Date: Thu, 30 Oct 2025 06:47:58 +0000
Subject: [PATCH] Add triple support to mcpu=help

Signed-off-by: Ruoyu Qiu <cabbaken at outlook.com>
---
 .../tools/llvm-objdump/mattr-mcpu-help.test     |  6 ++++++
 llvm/tools/llvm-objdump/llvm-objdump.cpp        | 17 +++++++++++++++++
 2 files changed, 23 insertions(+)

diff --git a/llvm/test/tools/llvm-objdump/mattr-mcpu-help.test b/llvm/test/tools/llvm-objdump/mattr-mcpu-help.test
index 65c426008fd6a..3475f0396d9b2 100644
--- a/llvm/test/tools/llvm-objdump/mattr-mcpu-help.test
+++ b/llvm/test/tools/llvm-objdump/mattr-mcpu-help.test
@@ -14,3 +14,9 @@ FileHeader:
   Data:            ELFDATA2LSB
   Type:            ET_EXEC
   Machine:         EM_X86_64
+
+# RUN: llvm-objdump --triple=x86_64 --mcpu=help 2>&1 \
+# RUN:   | FileCheck %s --check-prefix=CHECK-WITHOUT-DISASSEMBLING
+
+# CHECK-WITHOUT-DISASSEMBLING: Available CPUs for this target:
+# CHECK-WITHOUT-DISASSEMBLING: Available features for this target:
diff --git a/llvm/tools/llvm-objdump/llvm-objdump.cpp b/llvm/tools/llvm-objdump/llvm-objdump.cpp
index 3ec644a472bfc..5fe4420eb4f2d 100644
--- a/llvm/tools/llvm-objdump/llvm-objdump.cpp
+++ b/llvm/tools/llvm-objdump/llvm-objdump.cpp
@@ -3533,6 +3533,19 @@ commaSeparatedValues(const llvm::opt::InputArgList &InputArgs, int ID) {
   return Values;
 }
 
+static int MCPUHelp() {
+  if (!TripleName.empty()) {
+    std::string Error;
+    const Target *DummyTarget = TargetRegistry::lookupTarget(TripleName, Error);
+    if (!DummyTarget) {
+      outs() << Error << '\n';
+      return 2;
+    }
+    DummyTarget->createMCSubtargetInfo(TripleName, MCPU, "");
+  }
+  return 0;
+}
+
 static void parseOtoolOptions(const llvm::opt::InputArgList &InputArgs) {
   MachOOpt = true;
   FullLeadingAddr = true;
@@ -3826,6 +3839,10 @@ int llvm_objdump_main(int argc, char **argv, const llvm::ToolContext &) {
       !DisassembleSymbols.empty())
     Disassemble = true;
 
+  if (!Disassemble && MCPU == "help") {
+    return MCPUHelp();
+  }
+
   if (!ArchiveHeaders && !Disassemble && DwarfDumpType == DIDT_Null &&
       !DynamicRelocations && !FileHeaders && !PrivateHeaders && !RawClangAST &&
       !Relocations && !SectionHeaders && !SectionContents && !SymbolTable &&