[asan] Unconditionally enable GC of globals on COFF.

This change restores pre-r301225 behavior, where linker GC compatible global
instrumentation was used on COFF targets disregarding -f(no-)data-sections and/or
/Gw flags.

This instrumentation puts each global in a COMDAT with an ASan descriptor for that global.
It effectively enables -fdata-sections, but limits it to ASan-instrumented globals.

llvm-svn: 301374

Author: eugenis

clang/lib/CodeGen/BackendUtil.cpp

@@ -196,9 +196,8 @@ static void addSanitizerCoveragePass(const PassManagerBuilder &Builder,
 static bool asanUseGlobalsGC(const Triple &T, const CodeGenOptions &CGOpts) {
   switch (T.getObjectFormat()) {
   case Triple::MachO:
-    return true;
   case Triple::COFF:
-    return CGOpts.DataSections;
+    return true;
   case Triple::ELF:
     return CGOpts.DataSections && !CGOpts.DisableIntegratedAS;
   default:

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

@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -fsanitize=address -emit-llvm -o - -triple x86_64-windows-msvc %s | FileCheck %s --check-prefix=WITHOUT-GC
+// RUN: %clang_cc1 -fsanitize=address -emit-llvm -o - -triple x86_64-windows-msvc %s | FileCheck %s --check-prefix=WITH-GC
 // RUN: %clang_cc1 -fsanitize=address -emit-llvm -o - -triple x86_64-windows-msvc -fdata-sections %s | FileCheck %s --check-prefix=WITH-GC
 
 int global;