Add ASan metadata globals to @llvm.compiler.used under COFF

[aeubanks]

Summary

This matches ELF.

This makes the number of ASan failures under the new pass manager on
Windows go from 18 to 1.

Under the old pass manager, the ASan module pass was one of the very
last things run, so these globals didn't get removed due to GlobalOpt.
But with the NPM the ASan module pass that adds these globals are run
much earlier in the pipeline and GlobalOpt ends up removing them.

[aeubanks]

As for tests, I think making these work under the NPM, which we hopefully switch to soon, counts as tests.

[hans]

In D81175#2074045, @aeubanks wrote:

As for tests, I think making these work under the NPM, which we hopefully switch to soon, counts as tests.

Adding checks for @llvm.compiler.used in llvm/test/Instrumentation/AddressSanitizer/global_metadata_windows.ll would probably be good too.

[hans]

+eugenis who wrote the corresponding code for ELF

[aeubanks]

Add test

[aeubanks]

In D81175#2074382, @hans wrote:

In D81175#2074045, @aeubanks wrote:

As for tests, I think making these work under the NPM, which we hopefully switch to soon, counts as tests.

Adding checks for @llvm.compiler.used in llvm/test/Instrumentation/AddressSanitizer/global_metadata_windows.ll would probably be good too.

Ah I didn't see those tests, I forgot that the instrumentation itself has tests.

llvm/lib/Transforms/Instrumentation/AddressSanitizer.cpp

 }
 
 void ModuleAddressSanitizer::InstrumentGlobalsCOFF(
     IRBuilder<> &IRB, Module &M, ArrayRef<GlobalVariable *> ExtendedGlobals,
     ArrayRef<Constant *> MetadataInitializers) {
   assert(ExtendedGlobals.size() == MetadataInitializers.size());
   auto &DL = M.getDataLayout();
 
+  SmallVector<GlobalValue *, 16> MetadataGlobals(ExtendedGlobals.size());
   for (size_t i = 0; i < ExtendedGlobals.size(); i++) {
     Constant *Initializer = MetadataInitializers[i];
     GlobalVariable *G = ExtendedGlobals[i];
     GlobalVariable *Metadata =
         CreateMetadataGlobal(M, Initializer, G->getName());
+    MDNode *MD = MDNode::get(M.getContext(), ValueAsMetadata::get(G));
+    Metadata->setMetadata(LLVMContext::MD_associated, MD);
+    MetadataGlobals[i] = Metadata;
 
     // The MSVC linker always inserts padding when linking incrementally. We
     // cope with that by aligning each struct to its size, which must be a power
     // of two.
     unsigned SizeOfGlobalStruct = DL.getTypeAllocSize(Initializer->getType());
     assert(isPowerOf2_32(SizeOfGlobalStruct) &&
            "global metadata will not be padded appropriately");
     Metadata->setAlignment(assumeAligned(SizeOfGlobalStruct));
 
     SetComdatForGlobalMetadata(G, Metadata, "");
   }
+
+  // Update llvm.compiler.used, adding the new metadata globals. This is
+  // needed so that during LTO these variables stay alive.
+  if (!MetadataGlobals.empty())
+    appendToCompilerUsed(M, MetadataGlobals);
 }
 
 void ModuleAddressSanitizer::InstrumentGlobalsELF(
     IRBuilder<> &IRB, Module &M, ArrayRef<GlobalVariable *> ExtendedGlobals,
     ArrayRef<Constant *> MetadataInitializers,
     const std::string &UniqueModuleId) {
   assert(ExtendedGlobals.size() == MetadataInitializers.size());
 

llvm/test/Instrumentation/AddressSanitizer/global_metadata_windows.ll

 $mystr = comdat any
 
 ; CHECK: $dead_global = comdat noduplicates
 ; CHECK: $private_str = comdat noduplicates
 
 ; CHECK: @dead_global = global { i32, [60 x i8] } { i32 42, [60 x i8] zeroinitializer }, comdat, align 32
 ; CHECK: @private_str = internal constant { [8 x i8], [56 x i8] } { [8 x i8] c"private\00", [56 x i8] zeroinitializer }, comdat, align 32
 
-; CHECK: @__asan_global_dead_global = private global { {{.*}} }, section ".ASAN$GL", comdat($dead_global), align 64
-; CHECK: @__asan_global_private_str = private global { {{.*}} }, section ".ASAN$GL", comdat($private_str), align 64
+; CHECK: @__asan_global_dead_global = private global { {{.*}} }, section ".ASAN$GL", comdat($dead_global), align 64, !associated
+; CHECK: @__asan_global_private_str = private global { {{.*}} }, section ".ASAN$GL", comdat($private_str), align 64, !associated
+
+; CHECK: @llvm.compiler.used {{.*}} @__asan_global_dead_global {{.*}} @__asan_global_private_str {{.*}} section "llvm.metadata"
 
 @dead_global = local_unnamed_addr global i32 42, align 4
 @mystr = linkonce_odr unnamed_addr constant [5 x i8] c"main\00", comdat, align 1
 
 ; Private globals will get upgraded to internal linkage.
 @private_str = private unnamed_addr constant [8 x i8] c"private\00", align 1
 
 ; Function Attrs: nounwind uwtable