hwasan: Move ctor into a comdat.

[eugenis]

LGTM

llvm/trunk/lib/Transforms/Instrumentation/HWAddressSanitizer.cpp

bool HWAddressSanitizer::doInitialization(Module &M) {
 
   HwasanCtorFunction = nullptr;
   if (!CompileKernel) {
     std::tie(HwasanCtorFunction, std::ignore) =
         createSanitizerCtorAndInitFunctions(M, kHwasanModuleCtorName,
                                             kHwasanInitName,
                                             /*InitArgTypes=*/{},
                                             /*InitArgs=*/{});
-    appendToGlobalCtors(M, HwasanCtorFunction, 0);
-  }
+    Comdat *CtorComdat = M.getOrInsertComdat(kHwasanModuleCtorName);
+    HwasanCtorFunction->setComdat(CtorComdat);
+    appendToGlobalCtors(M, HwasanCtorFunction, 0, HwasanCtorFunction);
+
+    // Create a zero-length global in __hwasan_frame so that the linker will
+    // always create start and stop symbols.
+    //
+    // N.B. If we ever start creating associated metadata in this pass this
+    // global will need to be associated with the ctor.
+    Type *Int8Arr0Ty = ArrayType::get(Int8Ty, 0);
+    auto GV =
+        new GlobalVariable(M, Int8Arr0Ty, /*isConstantGlobal*/ true,
+                           GlobalVariable::PrivateLinkage,
+                           Constant::getNullValue(Int8Arr0Ty), "__hwasan");
+    GV->setSection(getFrameSection());
+    GV->setComdat(CtorComdat);
+    appendToCompilerUsed(M, GV);
 
-  // Create a call to __hwasan_init_frames.
-  if (HwasanCtorFunction) {
-    // Create a dummy frame description for the CTOR function.
-    // W/o it we would have to create the call to __hwasan_init_frames after
-    // all functions are instrumented (i.e. need to have a ModulePass).
-    createFrameGlobal(*HwasanCtorFunction, "");
     IRBuilder<> IRBCtor(HwasanCtorFunction->getEntryBlock().getTerminator());
     IRBCtor.CreateCall(
         declareSanitizerInitFunction(M, "__hwasan_init_frames",
                                      {Int8PtrTy, Int8PtrTy}),
         {createFrameSectionBound(M, Int8Ty, getFrameSectionBeg()),
          createFrameSectionBound(M, Int8Ty, getFrameSectionEnd())});
   }
 
void HWAddressSanitizer::createFrameGlobal(Function &F,
   auto PtrPairTy = StructType::get(F.getType(), DescrGV->getType());
   auto GV = new GlobalVariable(
       M, PtrPairTy, /*isConstantGlobal*/ true, GlobalVariable::PrivateLinkage,
       ConstantStruct::get(PtrPairTy, (Constant *)&F, (Constant *)DescrGV),
       "__hwasan");
   GV->setSection(getFrameSection());
   appendToCompilerUsed(M, GV);
   // Put GV into the F's Comadat so that if F is deleted GV can be deleted too.
-  if (&F != HwasanCtorFunction)
-    if (auto Comdat =
-            GetOrCreateFunctionComdat(F, TargetTriple, CurModuleUniqueId))
-      GV->setComdat(Comdat);
 }
 
 Value *HWAddressSanitizer::emitPrologue(IRBuilder<> &IRB,
                                         bool WithFrameRecord) {
   if (!Mapping.InTls)
     return getDynamicShadowNonTls(IRB);
 
   Value *SlotPtr = getHwasanThreadSlotPtr(IRB, IntptrTy);

llvm/trunk/test/Instrumentation/HWAddressSanitizer/basic.ll

 ; Test basic address sanitizer instrumentation.
 ;
 ; RUN: opt < %s -hwasan -hwasan-recover=0 -hwasan-with-ifunc=1 -hwasan-with-tls=0 -S | FileCheck %s --check-prefixes=CHECK,ABORT,DYNAMIC-SHADOW
 ; RUN: opt < %s -hwasan -hwasan-recover=1 -hwasan-with-ifunc=1 -hwasan-with-tls=0 -S | FileCheck %s --check-prefixes=CHECK,RECOVER,DYNAMIC-SHADOW
 ; RUN: opt < %s -hwasan -hwasan-recover=0 -hwasan-mapping-offset=0 -S | FileCheck %s --check-prefixes=CHECK,ABORT,ZERO-BASED-SHADOW
 ; RUN: opt < %s -hwasan -hwasan-recover=1 -hwasan-mapping-offset=0 -S | FileCheck %s --check-prefixes=CHECK,RECOVER,ZERO-BASED-SHADOW
 
+; CHECK: @llvm.global_ctors = appending global [1 x { i32, void ()*, i8* }] [{ i32, void ()*, i8* } { i32 0, void ()* @hwasan.module_ctor, i8* bitcast (void ()* @hwasan.module_ctor to i8*) }]
+; CHECK: @__hwasan = private constant [0 x i8] zeroinitializer, section "__hwasan_frames", comdat($hwasan.module_ctor)
+
 target datalayout = "e-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128"
 target triple = "aarch64--linux-android"
 
 define i8 @test_load8(i8* %a) sanitize_hwaddress {
 ; CHECK-LABEL: @test_load8(
 ; CHECK: %[[A:[^ ]*]] = ptrtoint i8* %a to i64
 ; CHECK: %[[B:[^ ]*]] = lshr i64 %[[A]], 56
 ; CHECK: %[[PTRTAG:[^ ]*]] = trunc i64 %[[B]] to i8

 
 entry:
   %b = load i8, i8 addrspace(256)* %a, align 4
   ret i8 %b
 }
 
 ; CHECK: declare void @__hwasan_init()
 
-; CHECK:      define internal void @hwasan.module_ctor() {
+; CHECK:      define internal void @hwasan.module_ctor() comdat {
 ; CHECK-NEXT:   call void @__hwasan_init()
 ; CHECK-NEXT:   call void @__hwasan_init_frames(
 ; CHECK-NEXT:   ret void
 ; CHECK-NEXT: }

llvm/trunk/test/Instrumentation/HWAddressSanitizer/with-calls.ll

 
 entry:
   %b = load i8, i8 addrspace(256)* %a, align 4
   ret i8 %b
 }
 
 ; CHECK: declare void @__hwasan_init()
 
-; CHECK:      define internal void @hwasan.module_ctor() {
+; CHECK:      define internal void @hwasan.module_ctor() comdat {
 ; CHECK-NEXT:   call void @__hwasan_init()
 ; CHECK-NEXT:   call void @__hwasan_init_frames(
 ; CHECK-NEXT:   ret void
 ; CHECK-NEXT: }