[DWARF v4] Suppressing the __debug_ranges section when there are no ranges

[wolfgangp]

Summary

One of the clang tests in debuginfo-tests (apple-accel.cpp) insists on checking for the existence of the __debug_ranges section (it requires darwin) even for trivial code which doesn't need any range lists. My recent patch to implement DWARF v5 rnglists suppressed the section for trivial cases and broke the test. To pacify the bots I disabled the suppression for DWARF 4, restoring the original behavior.

This patch (actually 2, debuginfo-tests is a separate repo) fixes the test and re-enables the suppression of unneeded DWARF 4 (and earlier) range lists.

@aprantl , @JDevlieghere Could you please make sure the test change makes sense. I am not that well-versed with Mach-O. I'm just trying to force the compiler to emit ranges.

[aprantl]

apple-accel.cpp

11

A comment why this is necessary would be nice.

apple-accel.cpp

 // REQUIRES: system-darwin
 // Test that clang produces the __apple accelerator tables,
 // e.g., __apple_types, correctly.
 // These sections are going to be retired in DWARF 5, so we hardcode
 // the DWARF version in the tests.
 // RUN: %clang %s %target_itanium_abi_host_triple -gdwarf-2 -O0 -c -g -o %t-ex
 // RUN: llvm-objdump -section-headers %t-ex | FileCheck %s
 // RUN: %clang %s %target_itanium_abi_host_triple -gdwarf-4 -O0 -c -g -o %t-ex
 // RUN: llvm-objdump -section-headers %t-ex | FileCheck %s
 
+__attribute__((section("1,__text_foo"))) void foo() {}
 int main (int argc, char const *argv[]) { return argc; }
 
 // CHECK: __debug_str
 // CHECK-NEXT: __debug_abbrev
 // CHECK-NEXT: __debug_info
 // CHECK-NEXT: __debug_ranges
 // CHECK-NEXT: __debug_macinfo
 // CHECK-NEXT: __apple_names
 // CHECK-NEXT: __apple_objc
 // CHECK-NEXT: __apple_namespac
 // CHECK-NEXT: __apple_types

lib/CodeGen/AsmPrinter/DwarfDebug.cpp

return llvm::all_of(
         });
   };
 
   if (!useRangesSection()) {
     assert(NoRangesPresent() && "No debug ranges expected.");
     return;
   }
 
-  if (getDwarfVersion() >= 5 && NoRangesPresent())
+  if (NoRangesPresent())
     return;
 
   // Start the dwarf ranges section.
   MCSymbol *TableEnd = nullptr;
   if (getDwarfVersion() >= 5) {
     Asm->OutStreamer->SwitchSection(
         Asm->getObjFileLowering().getDwarfRnglistsSection());
     TableEnd = emitRnglistsTableHeader(Asm, useSplitDwarf() ? SkeletonHolder