[asan] Allow -fsanitize-address-globals-dead-stripping with -fno-data-sections for ELF

[MaskRay]

Summary

-fdata-sections decides whether global variables go into different sections.
This is orthogonal to whether we place their metadata (.data or asan_globals) into different sections.

With -fno-data-sections, -fsanitize-address-globals-dead-stripping can still:

• deduplicate COMDAT asan.module_ctor and asan.module_dtor
• (with ld --gc-sections): for a data section (e.g. .data), if all global variables defined relative to it are unreferenced, discard them and associated asan_globals sections (rare but no need to exclude this case)

Similar to c7b90947bd0179d914fea56b52be545c8f60f20a for PE/COFF.

[kstoimenov]

LGTM

clang/lib/CodeGen/BackendUtil.cpp

 static bool asanUseGlobalsGC(const Triple &T, const CodeGenOptions &CGOpts) {
   if (!CGOpts.SanitizeAddressGlobalsDeadStripping)
     return false;
   switch (T.getObjectFormat()) {
   case Triple::MachO:
   case Triple::COFF:
     return true;
   case Triple::ELF:
-    return CGOpts.DataSections && !CGOpts.DisableIntegratedAS;
+    return !CGOpts.DisableIntegratedAS;
   case Triple::GOFF:
     llvm::report_fatal_error("ASan not implemented for GOFF");
   case Triple::XCOFF:
     llvm::report_fatal_error("ASan not implemented for XCOFF.");
   case Triple::Wasm:
   case Triple::UnknownObjectFormat:
     break;
   }

clang/test/CodeGen/asan-globals-gc.cpp

-// RUN: %clang_cc1 -fsanitize=address -fsanitize-address-globals-dead-stripping -emit-llvm -o - -triple x86_64-linux %s | FileCheck %s --check-prefix=WITHOUT-GC
+// RUN: %clang_cc1 -fsanitize=address -fsanitize-address-globals-dead-stripping -emit-llvm -o - -triple x86_64-linux %s | FileCheck %s --check-prefix=WITH-GC
 // RUN: %clang_cc1 -fsanitize=address -fsanitize-address-globals-dead-stripping -fdata-sections -emit-llvm -o - -triple x86_64-linux %s | FileCheck %s --check-prefix=WITH-GC
-// RUN: %clang_cc1 -fsanitize=address -fsanitize-address-globals-dead-stripping -fno-integrated-as -fdata-sections -emit-llvm -o - -triple x86_64-linux %s | FileCheck %s --check-prefix=WITHOUT-GC
 // RUN: %clang_cc1 -fsanitize=address -fsanitize-address-globals-dead-stripping -fno-integrated-as -emit-llvm -o - -triple x86_64-linux %s | FileCheck %s --check-prefix=WITHOUT-GC
 // RUN: %clang_cc1 -fsanitize=address -fdata-sections -emit-llvm -o - -triple x86_64-linux %s | FileCheck %s --check-prefix=WITHOUT-GC
 
 // RUN: %clang_cc1 -fsanitize=address -fsanitize-address-globals-dead-stripping -emit-llvm -o - -triple x86_64-windows-msvc %s | FileCheck %s --check-prefix=WITH-GC
 // RUN: %clang_cc1 -fsanitize=address -fsanitize-address-globals-dead-stripping -fdata-sections -emit-llvm -o - -triple x86_64-windows-msvc %s | FileCheck %s --check-prefix=WITH-GC
 // RUN: %clang_cc1 -fsanitize=address -fdata-sections -emit-llvm -o - -triple x86_64-windows-msvc %s | FileCheck %s --check-prefix=WITHOUT-GC
 
 // RUN: %clang_cc1 -fsanitize=address -fsanitize-address-globals-dead-stripping -emit-llvm -o - -triple x86_64-apple-macosx11 %s | FileCheck %s --check-prefix=WITH-GC
 // RUN: %clang_cc1 -fsanitize=address -fsanitize-address-globals-dead-stripping -fdata-sections -emit-llvm -o - -triple x86_64-apple-macosx11 %s | FileCheck %s --check-prefix=WITH-GC
 // RUN: %clang_cc1 -fsanitize=address -fdata-sections -emit-llvm -o - -triple x86_64-apple-macosx11 %s | FileCheck %s --check-prefix=WITHOUT-GC
 
 int global;
 
 // WITH-GC-NOT: call void @__asan_register_globals
 // WITHOUT-GC: call void @__asan_register_globals

clang/test/CodeGen/asan-no-globals-no-comdat.cpp

 // Test that on Linux asan constructor is placed in a comdat iff globals-gc is on.
 // Even if there are no globals in the module.
 
-// RUN: %clang_cc1 -fsanitize=address -fsanitize-address-globals-dead-stripping -emit-llvm -o - -triple x86_64-linux %s | FileCheck %s --check-prefix=WITHOUT-GC
-// RUN: %clang_cc1 -fsanitize=address -fsanitize-address-globals-dead-stripping -fdata-sections -emit-llvm -o - -triple x86_64-linux %s | FileCheck %s --check-prefix=WITH-GC
-// RUN: %clang_cc1 -fsanitize=address -fsanitize-address-globals-dead-stripping -fno-integrated-as -fdata-sections -emit-llvm -o - -triple x86_64-linux %s | FileCheck %s --check-prefix=WITHOUT-GC
+// RUN: %clang_cc1 -fsanitize=address -fsanitize-address-globals-dead-stripping -emit-llvm -o - -triple x86_64-linux %s | FileCheck %s --check-prefix=WITH-GC
 // RUN: %clang_cc1 -fsanitize=address -fsanitize-address-globals-dead-stripping -fno-integrated-as -emit-llvm -o - -triple x86_64-linux %s | FileCheck %s --check-prefix=WITHOUT-GC
 // RUN: %clang_cc1 -fsanitize=address -fdata-sections -emit-llvm -o - -triple x86_64-linux %s | FileCheck %s --check-prefix=WITHOUT-GC
 
 // WITH-GC: define internal void @asan.module_ctor() #[[#]] comdat {
 // WITHOUT-GC: define internal void @asan.module_ctor() #[[#]] {