5 files changed, 54 insertions, 143 deletions

diff --git a/clang/lib/CodeGen/CGDecl.cpp b/clang/lib/CodeGen/CGDecl.cpp
index f027ab941ac..db18ac49c6e 100644
--- a/clang/lib/CodeGen/CGDecl.cpp
+++ b/clang/lib/CodeGen/CGDecl.cpp
@@ -1077,16 +1077,17 @@ static llvm::Constant *constWithPadding(CodeGenModule &CGM, IsPattern isPattern,
   return constant;
 }
 
-Address CodeGenModule::createUnnamedGlobalFrom(const VarDecl &D,
-                                               llvm::Constant *Constant,
-                                               CharUnits Align) {
+static Address createUnnamedGlobalFrom(CodeGenModule &CGM, const VarDecl &D,
+                                       CGBuilderTy &Builder,
+                                       llvm::Constant *Constant,
+                                       CharUnits Align) {
   auto FunctionName = [&](const DeclContext *DC) -> std::string {
     if (const auto *FD = dyn_cast<FunctionDecl>(DC)) {
       if (const auto *CC = dyn_cast<CXXConstructorDecl>(FD))
         return CC->getNameAsString();
       if (const auto *CD = dyn_cast<CXXDestructorDecl>(FD))
         return CD->getNameAsString();
-      return getMangledName(FD);
+      return CGM.getMangledName(FD);
     } else if (const auto *OM = dyn_cast<ObjCMethodDecl>(DC)) {
       return OM->getNameAsString();
     } else if (isa<BlockDecl>(DC)) {
@@ -1098,39 +1099,22 @@ Address CodeGenModule::createUnnamedGlobalFrom(const VarDecl &D,
     }
   };
 
-  // Form a simple per-variable cache of these values in case we find we
-  // want to reuse them.
-  llvm::GlobalVariable *&CacheEntry = InitializerConstants[&D];
-  if (!CacheEntry || CacheEntry->getInitializer() != Constant) {
-    auto *Ty = Constant->getType();
-    bool isConstant = true;
-    llvm::GlobalVariable *InsertBefore = nullptr;
-    unsigned AS =
-        getContext().getTargetAddressSpace(getStringLiteralAddressSpace());
-    llvm::GlobalVariable *GV = new llvm::GlobalVariable(
-        getModule(), Ty, isConstant, llvm::GlobalValue::PrivateLinkage,
-        Constant,
-        "__const." + FunctionName(D.getParentFunctionOrMethod()) + "." +
-            D.getName(),
-        InsertBefore, llvm::GlobalValue::NotThreadLocal, AS);
-    GV->setAlignment(Align.getQuantity());
-    GV->setUnnamedAddr(llvm::GlobalValue::UnnamedAddr::Global);
-    CacheEntry = GV;
-  } else if (CacheEntry->getAlignment() < Align.getQuantity()) {
-    CacheEntry->setAlignment(Align.getQuantity());
-  }
-
-  return Address(CacheEntry, Align);
-}
-
-static Address createUnnamedGlobalForMemcpyFrom(CodeGenModule &CGM,
-                                                const VarDecl &D,
-                                                CGBuilderTy &Builder,
-                                                llvm::Constant *Constant,
-                                                CharUnits Align) {
-  Address SrcPtr = CGM.createUnnamedGlobalFrom(D, Constant, Align);
-  llvm::Type *BP = llvm::PointerType::getInt8PtrTy(CGM.getLLVMContext(),
-                                                   SrcPtr.getAddressSpace());
+  auto *Ty = Constant->getType();
+  bool isConstant = true;
+  llvm::GlobalVariable *InsertBefore = nullptr;
+  unsigned AS = CGM.getContext().getTargetAddressSpace(
+      CGM.getStringLiteralAddressSpace());
+  llvm::GlobalVariable *GV = new llvm::GlobalVariable(
+      CGM.getModule(), Ty, isConstant, llvm::GlobalValue::PrivateLinkage,
+      Constant,
+      "__const." + FunctionName(D.getParentFunctionOrMethod()) + "." +
+          D.getName(),
+      InsertBefore, llvm::GlobalValue::NotThreadLocal, AS);
+  GV->setAlignment(Align.getQuantity());
+  GV->setUnnamedAddr(llvm::GlobalValue::UnnamedAddr::Global);
+
+  Address SrcPtr = Address(GV, Align);
+  llvm::Type *BP = llvm::PointerType::getInt8PtrTy(CGM.getLLVMContext(), AS);
   if (SrcPtr.getType() != BP)
     SrcPtr = Builder.CreateBitCast(SrcPtr, BP);
   return SrcPtr;
@@ -1213,10 +1197,10 @@ static void emitStoresForConstant(CodeGenModule &CGM, const VarDecl &D,
   }
 
   // Copy from a global.
-  Builder.CreateMemCpy(Loc,
-                       createUnnamedGlobalForMemcpyFrom(
-                           CGM, D, Builder, constant, Loc.getAlignment()),
-                       SizeVal, isVolatile);
+  Builder.CreateMemCpy(
+      Loc,
+      createUnnamedGlobalFrom(CGM, D, Builder, constant, Loc.getAlignment()),
+      SizeVal, isVolatile);
 }
 
 static void emitStoresForZeroInit(CodeGenModule &CGM, const VarDecl &D,
@@ -1779,10 +1763,10 @@ void CodeGenFunction::EmitAutoVarInit(const AutoVarEmission &emission) {
       llvm::PHINode *Cur = Builder.CreatePHI(Begin.getType(), 2, "vla.cur");
       Cur->addIncoming(Begin.getPointer(), OriginBB);
       CharUnits CurAlign = Loc.getAlignment().alignmentOfArrayElement(EltSize);
-      Builder.CreateMemCpy(Address(Cur, CurAlign),
-                           createUnnamedGlobalForMemcpyFrom(
-                               CGM, D, Builder, Constant, ConstantAlign),
-                           BaseSizeInChars, isVolatile);
+      Builder.CreateMemCpy(
+          Address(Cur, CurAlign),
+          createUnnamedGlobalFrom(CGM, D, Builder, Constant, ConstantAlign),
+          BaseSizeInChars, isVolatile);
       llvm::Value *Next =
           Builder.CreateInBoundsGEP(Int8Ty, Cur, BaseSizeInChars, "vla.next");
       llvm::Value *Done = Builder.CreateICmpEQ(Next, End, "vla-init.isdone");
diff --git a/clang/lib/CodeGen/CGExpr.cpp b/clang/lib/CodeGen/CGExpr.cpp
index f0d8619faa3..d5ce4870f18 100644
--- a/clang/lib/CodeGen/CGExpr.cpp
+++ b/clang/lib/CodeGen/CGExpr.cpp
@@ -1422,11 +1422,10 @@ static ConstantEmissionKind checkVarTypeForConstantEmission(QualType type) {
 }
 
 /// Try to emit a reference to the given value without producing it as
-/// an l-value.  This is just an optimization, but it avoids us needing
-/// to emit global copies of variables if they're named without triggering
-/// a formal use in a context where we can't emit a direct reference to them,
-/// for instance if a block or lambda or a member of a local class uses a
-/// const int variable or constexpr variable from an enclosing function.
+/// an l-value.  This is actually more than an optimization: we can't
+/// produce an l-value for variables that we never actually captured
+/// in a block or lambda, which means const int variables or constexpr
+/// literals or similar.
 CodeGenFunction::ConstantEmission
 CodeGenFunction::tryEmitAsConstant(DeclRefExpr *refExpr) {
   ValueDecl *value = refExpr->getDecl();
@@ -2451,97 +2450,33 @@ static LValue EmitGlobalNamedRegister(const VarDecl *VD, CodeGenModule &CGM) {
   return LValue::MakeGlobalReg(Address(Ptr, Alignment), VD->getType());
 }
 
-/// Determine whether we can emit a reference to \p VD from the current
-/// context, despite not necessarily having seen an odr-use of the variable in
-/// this context.
-static bool canEmitSpuriousReferenceToVariable(CodeGenFunction &CGF,
-                                               const DeclRefExpr *E,
-                                               const VarDecl *VD,
-                                               bool IsConstant) {
-  // For a variable declared in an enclosing scope, do not emit a spurious
-  // reference even if we have a capture, as that will emit an unwarranted
-  // reference to our capture state, and will likely generate worse code than
-  // emitting a local copy.
-  if (E->refersToEnclosingVariableOrCapture())
-    return false;
-
-  // For a local declaration declared in this function, we can always reference
-  // it even if we don't have an odr-use.
-  if (VD->hasLocalStorage()) {
-    return VD->getDeclContext() ==
-           dyn_cast_or_null<DeclContext>(CGF.CurCodeDecl);
-  }
-
-  // For a global declaration, we can emit a reference to it if we know
-  // for sure that we are able to emit a definition of it.
-  VD = VD->getDefinition(CGF.getContext());
-  if (!VD)
-    return false;
-
-  // Don't emit a spurious reference if it might be to a variable that only
-  // exists on a different device / target.
-  // FIXME: This is unnecessarily broad. Check whether this would actually be a
-  // cross-target reference.
-  if (CGF.getLangOpts().OpenMP || CGF.getLangOpts().CUDA ||
-      CGF.getLangOpts().OpenCL) {
-    return false;
-  }
-
-  // We can emit a spurious reference only if the linkage implies that we'll
-  // be emitting a non-interposable symbol that will be retained until link
-  // time.
-  switch (CGF.CGM.getLLVMLinkageVarDefinition(VD, IsConstant)) {
-  case llvm::GlobalValue::ExternalLinkage:
-  case llvm::GlobalValue::LinkOnceODRLinkage:
-  case llvm::GlobalValue::WeakODRLinkage:
-  case llvm::GlobalValue::InternalLinkage:
-  case llvm::GlobalValue::PrivateLinkage:
-    return true;
-  default:
-    return false;
-  }
-}
-
 LValue CodeGenFunction::EmitDeclRefLValue(const DeclRefExpr *E) {
   const NamedDecl *ND = E->getDecl();
   QualType T = E->getType();
 
-  assert(E->isNonOdrUse() != NOUR_Unevaluated &&
-         "should not emit an unevaluated operand");
-
   if (const auto *VD = dyn_cast<VarDecl>(ND)) {
     // Global Named registers access via intrinsics only
     if (VD->getStorageClass() == SC_Register &&
         VD->hasAttr<AsmLabelAttr>() && !VD->isLocalVarDecl())
       return EmitGlobalNamedRegister(VD, CGM);
 
-    // If this DeclRefExpr does not constitute an odr-use of the variable,
-    // we're not permitted to emit a reference to it in general, and it might
-    // not be captured if capture would be necessary for a use. Emit the
-    // constant value directly instead.
-    if (E->isNonOdrUse() == NOUR_Constant &&
-        (VD->getType()->isReferenceType() ||
-         !canEmitSpuriousReferenceToVariable(*this, E, VD, true))) {
-      VD->getAnyInitializer(VD);
-      llvm::Constant *Val = ConstantEmitter(*this).emitAbstract(
-          E->getLocation(), *VD->evaluateValue(), VD->getType());
-      assert(Val && "failed to emit constant expression");
-
-      Address Addr = Address::invalid();
-      if (!VD->getType()->isReferenceType()) {
-        // Spill the constant value to a global.
-        Addr = CGM.createUnnamedGlobalFrom(*VD, Val,
-                                           getContext().getDeclAlign(VD));
-      } else {
-        // Should we be using the alignment of the constant pointer we emitted?
-        CharUnits Alignment =
-            getNaturalTypeAlignment(E->getType(),
-                                    /* BaseInfo= */ nullptr,
-                                    /* TBAAInfo= */ nullptr,
-                                    /* forPointeeType= */ true);
-        Addr = Address(Val, Alignment);
-      }
-      return MakeAddrLValue(Addr, T, AlignmentSource::Decl);
+    // A DeclRefExpr for a reference initialized by a constant expression can
+    // appear without being odr-used. Directly emit the constant initializer.
+    VD->getAnyInitializer(VD);
+    if (E->isNonOdrUse() == NOUR_Constant && VD->getType()->isReferenceType()) {
+      llvm::Constant *Val =
+        ConstantEmitter(*this).emitAbstract(E->getLocation(),
+                                            *VD->evaluateValue(),
+                                            VD->getType());
+      assert(Val && "failed to emit reference constant expression");
+      // FIXME: Eventually we will want to emit vector element references.
+
+      // Should we be using the alignment of the constant pointer we emitted?
+      CharUnits Alignment = getNaturalTypeAlignment(E->getType(),
+                                                    /* BaseInfo= */ nullptr,
+                                                    /* TBAAInfo= */ nullptr,
+                                                    /* forPointeeType= */ true);
+      return MakeAddrLValue(Address(Val, Alignment), T, AlignmentSource::Decl);
     }
 
     // FIXME: Handle other kinds of non-odr-use DeclRefExprs.
@@ -2577,7 +2512,7 @@ LValue CodeGenFunction::EmitDeclRefLValue(const DeclRefExpr *E) {
   // FIXME: We should be able to assert this for FunctionDecls as well!
   // FIXME: We should be able to assert this for all DeclRefExprs, not just
   // those with a valid source location.
-  assert((ND->isUsed(false) || !isa<VarDecl>(ND) || E->isNonOdrUse() ||
+  assert((ND->isUsed(false) || !isa<VarDecl>(ND) ||
           !E->getLocation().isValid()) &&
          "Should not use decl without marking it used!");
 
diff --git a/clang/lib/CodeGen/CGExprAgg.cpp b/clang/lib/CodeGen/CGExprAgg.cpp
index 3b1c5bf876e..a76058c1472 100644
--- a/clang/lib/CodeGen/CGExprAgg.cpp
+++ b/clang/lib/CodeGen/CGExprAgg.cpp
@@ -1352,8 +1352,7 @@ static bool isSimpleZero(const Expr *E, CodeGenFunction &CGF) {
   // (int*)0 - Null pointer expressions.
   if (const CastExpr *ICE = dyn_cast<CastExpr>(E))
     return ICE->getCastKind() == CK_NullToPointer &&
-           CGF.getTypes().isPointerZeroInitializable(E->getType()) &&
-           !E->HasSideEffects(CGF.getContext());
+        CGF.getTypes().isPointerZeroInitializable(E->getType());
   // '\0'
   if (const CharacterLiteral *CL = dyn_cast<CharacterLiteral>(E))
     return CL->getValue() == 0;
diff --git a/clang/lib/CodeGen/CGExprScalar.cpp b/clang/lib/CodeGen/CGExprScalar.cpp
index c4167537e79..267402dbef4 100644
--- a/clang/lib/CodeGen/CGExprScalar.cpp
+++ b/clang/lib/CodeGen/CGExprScalar.cpp
@@ -2148,14 +2148,14 @@ Value *ScalarExprEmitter::VisitCastExpr(CastExpr *CE) {
 
   case CK_NullToPointer:
     if (MustVisitNullValue(E))
-      CGF.EmitIgnoredExpr(E);
+      (void) Visit(E);
 
     return CGF.CGM.getNullPointer(cast<llvm::PointerType>(ConvertType(DestTy)),
                               DestTy);
 
   case CK_NullToMemberPointer: {
     if (MustVisitNullValue(E))
-      CGF.EmitIgnoredExpr(E);
+      (void) Visit(E);
 
     const MemberPointerType *MPT = CE->getType()->getAs<MemberPointerType>();
     return CGF.CGM.getCXXABI().EmitNullMemberPointer(MPT);
diff --git a/clang/lib/CodeGen/CodeGenModule.h b/clang/lib/CodeGen/CodeGenModule.h
index 95964afed4e..8c1bc0777de 100644
--- a/clang/lib/CodeGen/CodeGenModule.h
+++ b/clang/lib/CodeGen/CodeGenModule.h
@@ -362,10 +362,6 @@ private:
   llvm::SmallVector<std::pair<llvm::GlobalValue *, llvm::Constant *>, 8>
     GlobalValReplacements;
 
-  /// Variables for which we've emitted globals containing their constant
-  /// values along with the corresponding globals, for opportunistic reuse.
-  llvm::DenseMap<const VarDecl*, llvm::GlobalVariable*> InitializerConstants;
-
   /// Set of global decls for which we already diagnosed mangled name conflict.
   /// Required to not issue a warning (on a mangling conflict) multiple times
   /// for the same decl.
@@ -627,9 +623,6 @@ public:
     StaticLocalDeclGuardMap[D] = C;
   }
 
-  Address createUnnamedGlobalFrom(const VarDecl &D, llvm::Constant *Constant,
-                                  CharUnits Align);
-
   bool lookupRepresentativeDecl(StringRef MangledName,
                                 GlobalDecl &Result) const;