[MC] Allow annotating custom sections as zerofill

[egorzhdan]

Summary

This is already possible for e.g. cstring_literals, but the entry for zerofill was unnamed.

rdar://90336380

[jroelofs]

LGTM

llvm/lib/MC/MCSectionMachO.cpp

 
 /// SectionTypeDescriptors - These are strings that describe the various section
 /// types.  This *must* be kept in order with and stay synchronized with the
 /// section type list.
 static constexpr struct {
   StringLiteral AssemblerName, EnumName;
 } SectionTypeDescriptors[MachO::LAST_KNOWN_SECTION_TYPE + 1] = {
     {StringLiteral("regular"), StringLiteral("S_REGULAR")}, // 0x00
-    {StringLiteral(""), StringLiteral("S_ZEROFILL")},       // 0x01
+    {StringLiteral("zerofill"), StringLiteral("S_ZEROFILL")}, // 0x01
     {StringLiteral("cstring_literals"),
      StringLiteral("S_CSTRING_LITERALS")}, // 0x02
     {StringLiteral("4byte_literals"),
      StringLiteral("S_4BYTE_LITERALS")}, // 0x03
     {StringLiteral("8byte_literals"),
      StringLiteral("S_8BYTE_LITERALS")}, // 0x04
     {StringLiteral("literal_pointers"),
      StringLiteral("S_LITERAL_POINTERS")}, // 0x05

llvm/test/CodeGen/AArch64/clang-section-macho.ll

 ;RUN: llc -mtriple=arm64-apple-ios %s -o - | FileCheck %s
 
 define dso_local void @foo() #0 {
 entry:
   ret void
 }
 
 attributes #0 = { "implicit-section-name"="__TEXT,__mytext" }
 
 ; CHECK:      .section  __TEXT,__mytext
 ; CHECK-NEXT: .globl  _foo
+
+
+define dso_local void @bar() #1 {
+entry:
+  ret void
+}
+
+attributes #1 = { "implicit-section-name"="__EDATA,zerofill" }
+
+; CHECK:      .section  __EDATA,zerofill
+; CHECK-NEXT: .globl  _bar