[AArch64][SME] Remove Darwin compile error for ABI support routine calls.

These are allowed for Darwin and use the same ABI.

Author: aemerson

llvm/lib/Target/AArch64/AArch64RegisterInfo.cpp

@@ -233,13 +233,9 @@ AArch64RegisterInfo::getDarwinCallPreservedMask(const MachineFunction &MF,
     report_fatal_error(
         "Calling convention SVE_VectorCall is unsupported on Darwin.");
   if (CC == CallingConv::AArch64_SME_ABI_Support_Routines_PreserveMost_From_X0)
-    report_fatal_error(
-        "Calling convention AArch64_SME_ABI_Support_Routines_PreserveMost_From_X0 is "
-        "unsupported on Darwin.");
+    return CSR_AArch64_SME_ABI_Support_Routines_PreserveMost_From_X0_RegMask;
   if (CC == CallingConv::AArch64_SME_ABI_Support_Routines_PreserveMost_From_X2)
-    report_fatal_error(
-        "Calling convention AArch64_SME_ABI_Support_Routines_PreserveMost_From_X2 is "
-        "unsupported on Darwin.");
+    return CSR_AArch64_SME_ABI_Support_Routines_PreserveMost_From_X2_RegMask;
   if (CC == CallingConv::CFGuard_Check)
     report_fatal_error(
         "Calling convention CFGuard_Check is unsupported on Darwin.");

llvm/test/CodeGen/AArch64/sme-support-routines-calling-convention.ll

@@ -1,5 +1,7 @@
 ; RUN: llc -mtriple=aarch64-linux-gnu -mattr=+sme -verify-machineinstrs < %s | FileCheck %s
+; RUN: llc -mtriple=aarch64-apple-darwin -mattr=+sme -verify-machineinstrs < %s | FileCheck %s --check-prefix=DARWIN
 ; RUN: llc -mtriple=aarch64-linux-gnu -mattr=+sme -verify-machineinstrs -stop-after=finalize-isel < %s | FileCheck %s --check-prefix=CHECK-CSRMASK
+; RUN: llc -mtriple=aarch64-apple-darwin -mattr=+sme -verify-machineinstrs -stop-after=finalize-isel < %s | FileCheck %s --check-prefix=CHECK-CSRMASK
 
 ; Test that the PCS attribute is accepted and uses the correct register mask.
 ;
@@ -11,6 +13,11 @@ define void @test_sme_calling_convention_x0() nounwind {
 ; CHECK-NEXT:    bl __arm_tpidr2_save
 ; CHECK-NEXT:    ldr x30, [sp], #16 // 8-byte Folded Reload
 ; CHECK-NEXT:    ret
+; DARWIN-LABEL: test_sme_calling_convention_x0:
+; DARWIN:    stp	x29, x30, [sp, #-16]!
+; DARWIN:    bl ___arm_tpidr2_save
+; DARWIN:    ldp	x29, x30, [sp], #16
+; DARWIN:    ret
 ;
 ; CHECK-CSRMASK-LABEL: name: test_sme_calling_convention_x0
 ; CHECK-CSRMASK: BL @__arm_tpidr2_save, csr_aarch64_sme_abi_support_routines_preservemost_from_x0
@@ -25,6 +32,11 @@ define i64 @test_sme_calling_convention_x2() nounwind {
 ; CHECK-NEXT:    bl __arm_sme_state
 ; CHECK-NEXT:    ldr x30, [sp], #16 // 8-byte Folded Reload
 ; CHECK-NEXT:    ret
+; DARWIN-LABEL: test_sme_calling_convention_x2:
+; DARWIN:    stp	x29, x30, [sp, #-16]!
+; DARWIN:    bl ___arm_sme_state
+; DARWIN:    ldp	x29, x30, [sp], #16
+; DARWIN:    ret
 ;
 ; CHECK-CSRMASK-LABEL: name: test_sme_calling_convention_x2
 ; CHECK-CSRMASK: BL @__arm_sme_state, csr_aarch64_sme_abi_support_routines_preservemost_from_x2