Compute and preserve alignment more faithfully in IR-generation.

Introduce an Address type to bundle a pointer value with an
alignment.  Introduce APIs on CGBuilderTy to work with Address
values.  Change core APIs on CGF/CGM to traffic in Address where
appropriate.  Require alignments to be non-zero.  Update a ton
of code to compute and propagate alignment information.

As part of this, I've promoted CGBuiltin's EmitPointerWithAlignment
helper function to CGF and made use of it in a number of places in
the expression emitter.

The end result is that we should now be significantly more correct
when performing operations on objects that are locally known to
be under-aligned.  Since alignment is not reliably tracked in the
type system, there are inherent limits to this, but at least we
are no longer confused by standard operations like derived-to-base
conversions and array-to-pointer decay.  I've also fixed a large
number of bugs where we were applying the complete-object alignment
to a pointer instead of the non-virtual alignment, although most of
these were hidden by the very conservative approach we took with
member alignment.

Also, because IRGen now reliably asserts on zero alignments, we
should no longer be subject to an absurd but frustrating recurring
bug where an incomplete type would report a zero alignment and then
we'd naively do a alignmentAtOffset on it and emit code using an
alignment equal to the largest power-of-two factor of the offset.

We should also now be emitting much more aggressive alignment
attributes in the presence of over-alignment.  In particular,
field access now uses alignmentAtOffset instead of min.

Several times in this patch, I had to change the existing
code-generation pattern in order to more effectively use
the Address APIs.  For the most part, this seems to be a strict
improvement, like doing pointer arithmetic with GEPs instead of
ptrtoint.  That said, I've tried very hard to not change semantics,
but it is likely that I've failed in a few places, for which I
apologize.

ABIArgInfo now always carries the assumed alignment of indirect and
indirect byval arguments.  In order to cut down on what was already
a dauntingly large patch, I changed the code to never set align
attributes in the IR on non-byval indirect arguments.  That is,
we still generate code which assumes that indirect arguments have
the given alignment, but we don't express this information to the
backend except where it's semantically required (i.e. on byvals).
This is likely a minor regression for those targets that did provide
this information, but it'll be trivial to add it back in a later
patch.

I partially punted on applying this work to CGBuiltin.  Please
do not add more uses of the CreateDefaultAligned{Load,Store}
APIs; they will be going away eventually.

llvm-svn: 246985

1 files changed, 53 insertions, 41 deletions

diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
index 1177557aca0..e76ee12512e 100644
--- a/clang/lib/CodeGen/CodeGenModule.cpp
+++ b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -12,6 +12,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "CodeGenModule.h"
+#include "CGBlocks.h"
 #include "CGCUDARuntime.h"
 #include "CGCXXABI.h"
 #include "CGCall.h"
@@ -106,7 +107,9 @@ CodeGenModule::CodeGenModule(ASTContext &C, const HeaderSearchOptions &HSO,
   DoubleTy = llvm::Type::getDoubleTy(LLVMContext);
   PointerWidthInBits = C.getTargetInfo().getPointerWidth(0);
   PointerAlignInBytes =
-  C.toCharUnitsFromBits(C.getTargetInfo().getPointerAlign(0)).getQuantity();
+    C.toCharUnitsFromBits(C.getTargetInfo().getPointerAlign(0)).getQuantity();
+  IntAlignInBytes =
+    C.toCharUnitsFromBits(C.getTargetInfo().getIntAlign()).getQuantity();
   IntTy = llvm::IntegerType::get(LLVMContext, C.getTargetInfo().getIntWidth());
   IntPtrTy = llvm::IntegerType::get(LLVMContext, PointerWidthInBits);
   Int8PtrTy = Int8Ty->getPointerTo(0);
@@ -1303,7 +1306,7 @@ bool CodeGenModule::MayBeEmittedEagerly(const ValueDecl *Global) {
   return true;
 }
 
-llvm::Constant *CodeGenModule::GetAddrOfUuidDescriptor(
+ConstantAddress CodeGenModule::GetAddrOfUuidDescriptor(
     const CXXUuidofExpr* E) {
   // Sema has verified that IIDSource has a __declspec(uuid()), and that its
   // well-formed.
@@ -1311,9 +1314,12 @@ llvm::Constant *CodeGenModule::GetAddrOfUuidDescriptor(
   std::string Name = "_GUID_" + Uuid.lower();
   std::replace(Name.begin(), Name.end(), '-', '_');
 
+  // Contains a 32-bit field.
+  CharUnits Alignment = CharUnits::fromQuantity(4);
+
   // Look for an existing global.
   if (llvm::GlobalVariable *GV = getModule().getNamedGlobal(Name))
-    return GV;
+    return ConstantAddress(GV, Alignment);
 
   llvm::Constant *Init = EmitUuidofInitializer(Uuid);
   assert(Init && "failed to initialize as constant");
@@ -1323,20 +1329,22 @@ llvm::Constant *CodeGenModule::GetAddrOfUuidDescriptor(
       /*isConstant=*/true, llvm::GlobalValue::LinkOnceODRLinkage, Init, Name);
   if (supportsCOMDAT())
     GV->setComdat(TheModule.getOrInsertComdat(GV->getName()));
-  return GV;
+  return ConstantAddress(GV, Alignment);
 }
 
-llvm::Constant *CodeGenModule::GetWeakRefReference(const ValueDecl *VD) {
+ConstantAddress CodeGenModule::GetWeakRefReference(const ValueDecl *VD) {
   const AliasAttr *AA = VD->getAttr<AliasAttr>();
   assert(AA && "No alias?");
 
+  CharUnits Alignment = getContext().getDeclAlign(VD);
   llvm::Type *DeclTy = getTypes().ConvertTypeForMem(VD->getType());
 
   // See if there is already something with the target's name in the module.
   llvm::GlobalValue *Entry = GetGlobalValue(AA->getAliasee());
   if (Entry) {
     unsigned AS = getContext().getTargetAddressSpace(VD->getType());
-    return llvm::ConstantExpr::getBitCast(Entry, DeclTy->getPointerTo(AS));
+    auto Ptr = llvm::ConstantExpr::getBitCast(Entry, DeclTy->getPointerTo(AS));
+    return ConstantAddress(Ptr, Alignment);
   }
 
   llvm::Constant *Aliasee;
@@ -1353,7 +1361,7 @@ llvm::Constant *CodeGenModule::GetWeakRefReference(const ValueDecl *VD) {
   F->setLinkage(llvm::Function::ExternalWeakLinkage);
   WeakRefReferences.insert(F);
 
-  return Aliasee;
+  return ConstantAddress(Aliasee, Alignment);
 }
 
 void CodeGenModule::EmitGlobal(GlobalDecl GD) {
@@ -2732,7 +2740,7 @@ GetConstantStringEntry(llvm::StringMap<llvm::GlobalVariable *> &Map,
   return *Map.insert(std::make_pair(String, nullptr)).first;
 }
 
-llvm::Constant *
+ConstantAddress
 CodeGenModule::GetAddrOfConstantCFString(const StringLiteral *Literal) {
   unsigned StringLength = 0;
   bool isUTF16 = false;
@@ -2742,7 +2750,7 @@ CodeGenModule::GetAddrOfConstantCFString(const StringLiteral *Literal) {
                                StringLength);
 
   if (auto *C = Entry.second)
-    return C;
+    return ConstantAddress(C, CharUnits::fromQuantity(C->getAlignment()));
 
   llvm::Constant *Zero = llvm::Constant::getNullValue(Int32Ty);
   llvm::Constant *Zeros[] = { Zero, Zero };
@@ -2819,25 +2827,28 @@ CodeGenModule::GetAddrOfConstantCFString(const StringLiteral *Literal) {
   Ty = getTypes().ConvertType(getContext().LongTy);
   Fields[3] = llvm::ConstantInt::get(Ty, StringLength);
 
+  CharUnits Alignment = getPointerAlign();
+
   // The struct.
   C = llvm::ConstantStruct::get(STy, Fields);
   GV = new llvm::GlobalVariable(getModule(), C->getType(), true,
                                 llvm::GlobalVariable::PrivateLinkage, C,
                                 "_unnamed_cfstring_");
   GV->setSection("__DATA,__cfstring");
+  GV->setAlignment(Alignment.getQuantity());
   Entry.second = GV;
 
-  return GV;
+  return ConstantAddress(GV, Alignment);
 }
 
-llvm::GlobalVariable *
+ConstantAddress
 CodeGenModule::GetAddrOfConstantString(const StringLiteral *Literal) {
   unsigned StringLength = 0;
   llvm::StringMapEntry<llvm::GlobalVariable *> &Entry =
       GetConstantStringEntry(CFConstantStringMap, Literal, StringLength);
 
   if (auto *C = Entry.second)
-    return C;
+    return ConstantAddress(C, CharUnits::fromQuantity(C->getAlignment()));
   
   llvm::Constant *Zero = llvm::Constant::getNullValue(Int32Ty);
   llvm::Constant *Zeros[] = { Zero, Zero };
@@ -2930,10 +2941,12 @@ CodeGenModule::GetAddrOfConstantString(const StringLiteral *Literal) {
   Fields[2] = llvm::ConstantInt::get(Ty, StringLength);
   
   // The struct.
+  CharUnits Alignment = getPointerAlign();
   C = llvm::ConstantStruct::get(NSConstantStringType, Fields);
   GV = new llvm::GlobalVariable(getModule(), C->getType(), true,
                                 llvm::GlobalVariable::PrivateLinkage, C,
                                 "_unnamed_nsstring_");
+  GV->setAlignment(Alignment.getQuantity());
   const char *NSStringSection = "__OBJC,__cstring_object,regular,no_dead_strip";
   const char *NSStringNonFragileABISection =
       "__DATA,__objc_stringobj,regular,no_dead_strip";
@@ -2943,7 +2956,7 @@ CodeGenModule::GetAddrOfConstantString(const StringLiteral *Literal) {
                      : NSStringSection);
   Entry.second = GV;
 
-  return GV;
+  return ConstantAddress(GV, Alignment);
 }
 
 QualType CodeGenModule::getObjCFastEnumerationStateType() {
@@ -3022,7 +3035,7 @@ CodeGenModule::GetConstantArrayFromStringLiteral(const StringLiteral *E) {
 static llvm::GlobalVariable *
 GenerateStringLiteral(llvm::Constant *C, llvm::GlobalValue::LinkageTypes LT,
                       CodeGenModule &CGM, StringRef GlobalName,
-                      unsigned Alignment) {
+                      CharUnits Alignment) {
   // OpenCL v1.2 s6.5.3: a string literal is in the constant address space.
   unsigned AddrSpace = 0;
   if (CGM.getLangOpts().OpenCL)
@@ -3033,7 +3046,7 @@ GenerateStringLiteral(llvm::Constant *C, llvm::GlobalValue::LinkageTypes LT,
   auto *GV = new llvm::GlobalVariable(
       M, C->getType(), !CGM.getLangOpts().WritableStrings, LT, C, GlobalName,
       nullptr, llvm::GlobalVariable::NotThreadLocal, AddrSpace);
-  GV->setAlignment(Alignment);
+  GV->setAlignment(Alignment.getQuantity());
   GV->setUnnamedAddr(true);
   if (GV->isWeakForLinker()) {
     assert(CGM.supportsCOMDAT() && "Only COFF uses weak string literals");
@@ -3045,20 +3058,19 @@ GenerateStringLiteral(llvm::Constant *C, llvm::GlobalValue::LinkageTypes LT,
 
 /// GetAddrOfConstantStringFromLiteral - Return a pointer to a
 /// constant array for the given string literal.
-llvm::GlobalVariable *
+ConstantAddress
 CodeGenModule::GetAddrOfConstantStringFromLiteral(const StringLiteral *S,
                                                   StringRef Name) {
-  auto Alignment =
-      getContext().getAlignOfGlobalVarInChars(S->getType()).getQuantity();
+  CharUnits Alignment = getContext().getAlignOfGlobalVarInChars(S->getType());
 
   llvm::Constant *C = GetConstantArrayFromStringLiteral(S);
   llvm::GlobalVariable **Entry = nullptr;
   if (!LangOpts.WritableStrings) {
     Entry = &ConstantStringMap[C];
     if (auto GV = *Entry) {
-      if (Alignment > GV->getAlignment())
-        GV->setAlignment(Alignment);
-      return GV;
+      if (Alignment.getQuantity() > GV->getAlignment())
+        GV->setAlignment(Alignment.getQuantity());
+      return ConstantAddress(GV, Alignment);
     }
   }
 
@@ -3088,12 +3100,12 @@ CodeGenModule::GetAddrOfConstantStringFromLiteral(const StringLiteral *S,
 
   SanitizerMD->reportGlobalToASan(GV, S->getStrTokenLoc(0), "<string literal>",
                                   QualType());
-  return GV;
+  return ConstantAddress(GV, Alignment);
 }
 
 /// GetAddrOfConstantStringFromObjCEncode - Return a pointer to a constant
 /// array for the given ObjCEncodeExpr node.
-llvm::GlobalVariable *
+ConstantAddress
 CodeGenModule::GetAddrOfConstantStringFromObjCEncode(const ObjCEncodeExpr *E) {
   std::string Str;
   getContext().getObjCEncodingForType(E->getEncodedType(), Str);
@@ -3104,14 +3116,11 @@ CodeGenModule::GetAddrOfConstantStringFromObjCEncode(const ObjCEncodeExpr *E) {
 /// GetAddrOfConstantCString - Returns a pointer to a character array containing
 /// the literal and a terminating '\0' character.
 /// The result has pointer to array type.
-llvm::GlobalVariable *CodeGenModule::GetAddrOfConstantCString(
-    const std::string &Str, const char *GlobalName, unsigned Alignment) {
+ConstantAddress CodeGenModule::GetAddrOfConstantCString(
+    const std::string &Str, const char *GlobalName) {
   StringRef StrWithNull(Str.c_str(), Str.size() + 1);
-  if (Alignment == 0) {
-    Alignment = getContext()
-                    .getAlignOfGlobalVarInChars(getContext().CharTy)
-                    .getQuantity();
-  }
+  CharUnits Alignment =
+    getContext().getAlignOfGlobalVarInChars(getContext().CharTy);
 
   llvm::Constant *C =
       llvm::ConstantDataArray::getString(getLLVMContext(), StrWithNull, false);
@@ -3121,9 +3130,9 @@ llvm::GlobalVariable *CodeGenModule::GetAddrOfConstantCString(
   if (!LangOpts.WritableStrings) {
     Entry = &ConstantStringMap[C];
     if (auto GV = *Entry) {
-      if (Alignment > GV->getAlignment())
-        GV->setAlignment(Alignment);
-      return GV;
+      if (Alignment.getQuantity() > GV->getAlignment())
+        GV->setAlignment(Alignment.getQuantity());
+      return ConstantAddress(GV, Alignment);
     }
   }
 
@@ -3135,10 +3144,10 @@ llvm::GlobalVariable *CodeGenModule::GetAddrOfConstantCString(
                                   GlobalName, Alignment);
   if (Entry)
     *Entry = GV;
-  return GV;
+  return ConstantAddress(GV, Alignment);
 }
 
-llvm::Constant *CodeGenModule::GetAddrOfGlobalTemporary(
+ConstantAddress CodeGenModule::GetAddrOfGlobalTemporary(
     const MaterializeTemporaryExpr *E, const Expr *Init) {
   assert((E->getStorageDuration() == SD_Static ||
           E->getStorageDuration() == SD_Thread) && "not a global temporary");
@@ -3150,8 +3159,10 @@ llvm::Constant *CodeGenModule::GetAddrOfGlobalTemporary(
   if (Init == E->GetTemporaryExpr())
     MaterializedType = E->getType();
 
+  CharUnits Align = getContext().getTypeAlignInChars(MaterializedType);
+
   if (llvm::Constant *Slot = MaterializedGlobalTemporaryMap[E])
-    return Slot;
+    return ConstantAddress(Slot, Align);
 
   // FIXME: If an externally-visible declaration extends multiple temporaries,
   // we need to give each temporary the same name in every translation unit (and
@@ -3215,14 +3226,13 @@ llvm::Constant *CodeGenModule::GetAddrOfGlobalTemporary(
       /*InsertBefore=*/nullptr, llvm::GlobalVariable::NotThreadLocal,
       AddrSpace);
   setGlobalVisibility(GV, VD);
-  GV->setAlignment(
-      getContext().getTypeAlignInChars(MaterializedType).getQuantity());
+  GV->setAlignment(Align.getQuantity());
   if (supportsCOMDAT() && GV->isWeakForLinker())
     GV->setComdat(TheModule.getOrInsertComdat(GV->getName()));
   if (VD->getTLSKind())
     setTLSMode(GV, *VD);
   MaterializedGlobalTemporaryMap[E] = GV;
-  return GV;
+  return ConstantAddress(GV, Align);
 }
 
 /// EmitObjCPropertyImplementations - Emit information for synthesized
@@ -3676,7 +3686,7 @@ void CodeGenFunction::EmitDeclMetadata() {
 
   for (auto &I : LocalDeclMap) {
     const Decl *D = I.first;
-    llvm::Value *Addr = I.second;
+    llvm::Value *Addr = I.second.getPointer();
     if (auto *Alloca = dyn_cast<llvm::AllocaInst>(Addr)) {
       llvm::Value *DAddr = GetPointerConstant(getLLVMContext(), D);
       Alloca->setMetadata(
@@ -3785,8 +3795,10 @@ void CodeGenModule::EmitOMPThreadPrivateDecl(const OMPThreadPrivateDecl *D) {
         VD->getAnyInitializer() &&
         !VD->getAnyInitializer()->isConstantInitializer(getContext(),
                                                         /*ForRef=*/false);
+
+    Address Addr(GetAddrOfGlobalVar(VD), getContext().getDeclAlign(VD));
     if (auto InitFunction = getOpenMPRuntime().emitThreadPrivateVarDefinition(
-            VD, GetAddrOfGlobalVar(VD), RefExpr->getLocStart(), PerformInit))
+            VD, Addr, RefExpr->getLocStart(), PerformInit))
       CXXGlobalInits.push_back(InitFunction);
   }
 }