[AArch64] Restrict .variant_pcs directive to ELF targets (#138924)

Directive was implemented in c87bd2d to support lazy binding and is
emitted for vector PCS functions. It's specific to ELF but is currently
emitted for all binary formats and crashing on non-ELF targets.

Fixes #138260

---------

Co-authored-by: Cullen Rhodes <cullen.rhodes@arm.com>

Author: MacDue

llvm/lib/Target/AArch64/AArch64AsmPrinter.cpp

@@ -1344,19 +1344,20 @@ AArch64AsmPrinter::getCodeViewJumpTableInfo(int JTI,
 }
 
 void AArch64AsmPrinter::emitFunctionEntryLabel() {
-  if (MF->getFunction().getCallingConv() == CallingConv::AArch64_VectorCall ||
-      MF->getFunction().getCallingConv() ==
-          CallingConv::AArch64_SVE_VectorCall ||
-      MF->getInfo<AArch64FunctionInfo>()->isSVECC()) {
+  const Triple &TT = TM.getTargetTriple();
+  if (TT.isOSBinFormatELF() &&
+      (MF->getFunction().getCallingConv() == CallingConv::AArch64_VectorCall ||
+       MF->getFunction().getCallingConv() ==
+           CallingConv::AArch64_SVE_VectorCall ||
+       MF->getInfo<AArch64FunctionInfo>()->isSVECC())) {
     auto *TS =
         static_cast<AArch64TargetStreamer *>(OutStreamer->getTargetStreamer());
     TS->emitDirectiveVariantPCS(CurrentFnSym);
   }
 
   AsmPrinter::emitFunctionEntryLabel();
 
-  if (TM.getTargetTriple().isWindowsArm64EC() &&
-      !MF->getFunction().hasLocalLinkage()) {
+  if (TT.isWindowsArm64EC() && !MF->getFunction().hasLocalLinkage()) {
     // For ARM64EC targets, a function definition's name is mangled differently
     // from the normal symbol, emit required aliases here.
     auto emitFunctionAlias = [&](MCSymbol *Src, MCSymbol *Dst) {

llvm/test/CodeGen/AArch64/variant-pcs.ll

@@ -2,6 +2,9 @@
 ; RUN: llc -mtriple=aarch64-linux-gnu -mattr=+sve -filetype=obj -o - %s \
 ; RUN:   | llvm-readobj --symbols - | FileCheck %s --check-prefix=CHECK-OBJ
 
+; Check we don't crash when using a Mach-O object format.
+; RUN: llc -mtriple=arm64-apple-macosx15.0.0 -mattr=+sve -filetype=obj -o /dev/null %s
+
 define i32 @base_pcs() {
 ; CHECK-ASM-LABEL: base_pcs:
 ; CHECK-ASM-NOT: .variant_pcs