Merged master:b198de67e0b into amd-gfx:6357d679802

Local branch amd-gfx 6357d67 Merged master:1c7037a2a55 into amd-gfx:f3c1125efa9 Remote branch master b198de6 Merge some of the PCH object support with modular codegen
jaebaek · Jul 22, 2020 · c1fd4c1 · c1fd4c1
2 parents 6357d67 + b198de6
commit c1fd4c1
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diff --git a/clang-tools-extra/clangd/unittests/CMakeLists.txt b/clang-tools-extra/clangd/unittests/CMakeLists.txt
@@ -22,10 +22,6 @@ if(CLANG_BUILT_STANDALONE)
   endif()
 endif()
 
-if (CXX_SUPPORTS_SUGGEST_OVERRIDE_FLAG)
-  add_definitions("-Wno-suggest-override")
-endif()
-
 if (CLANGD_ENABLE_REMOTE)
   include_directories(${CMAKE_CURRENT_BINARY_DIR}/../index/remote)
   add_definitions(-DGOOGLE_PROTOBUF_NO_RTTI=1)

diff --git a/clang-tools-extra/unittests/CMakeLists.txt b/clang-tools-extra/unittests/CMakeLists.txt
@@ -5,10 +5,6 @@ function(add_extra_unittest test_dirname)
   add_unittest(ExtraToolsUnitTests ${test_dirname} ${ARGN})
 endfunction()
 
-if (CXX_SUPPORTS_SUGGEST_OVERRIDE_FLAG)
-  add_definitions("-Wno-suggest-override")
-endif()
-
 add_subdirectory(clang-apply-replacements)
 add_subdirectory(clang-change-namespace)
 add_subdirectory(clang-doc)

diff --git a/clang/CMakeLists.txt b/clang/CMakeLists.txt
@@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 3.4.3)
+cmake_minimum_required(VERSION 3.13.4)
 
 if(POLICY CMP0075)
   cmake_policy(SET CMP0075 NEW)

diff --git a/clang/include/clang/AST/ExternalASTSource.h b/clang/include/clang/AST/ExternalASTSource.h
@@ -161,10 +161,6 @@ class ExternalASTSource : public RefCountedBase<ExternalASTSource> {
   /// Retrieve the module that corresponds to the given module ID.
   virtual Module *getModule(unsigned ID) { return nullptr; }
 
-  /// Determine whether D comes from a PCH which was built with a corresponding
-  /// object file.
-  virtual bool DeclIsFromPCHWithObjectFile(const Decl *D) { return false; }
-
   /// Return a descriptor for the corresponding module, if one exists.
   virtual llvm::Optional<ASTSourceDescriptor> getSourceDescriptor(unsigned ID);
 

diff --git a/clang/include/clang/Basic/BuiltinsPPC.def b/clang/include/clang/Basic/BuiltinsPPC.def
@@ -467,7 +467,7 @@ BUILTIN(__builtin_vsx_xxsldwi, "v.", "t")
 
 BUILTIN(__builtin_vsx_xxeval, "V2ULLiV2ULLiV2ULLiV2ULLiIi", "")
 
-BUILTIN(__builtin_vsx_xvtlsbb, "iV16Ucb", "")
+BUILTIN(__builtin_vsx_xvtlsbb, "iV16UcUi", "")
 
 // P10 Vector Permute Extended built-in.
 BUILTIN(__builtin_vsx_xxpermx, "V16UcV16UcV16UcV16UcIi", "")

diff --git a/clang/include/clang/Sema/MultiplexExternalSemaSource.h b/clang/include/clang/Sema/MultiplexExternalSemaSource.h
@@ -153,8 +153,6 @@ class MultiplexExternalSemaSource : public ExternalSemaSource {
   /// Retrieve the module that corresponds to the given module ID.
   Module *getModule(unsigned ID) override;
 
-  bool DeclIsFromPCHWithObjectFile(const Decl *D) override;
-
   /// Perform layout on the given record.
   ///
   /// This routine allows the external AST source to provide an specific

diff --git a/clang/include/clang/Serialization/ASTReader.h b/clang/include/clang/Serialization/ASTReader.h
@@ -2085,8 +2085,6 @@ class ASTReader
   /// Note: overrides method in ExternalASTSource
   Module *getModule(unsigned ID) override;
 
-  bool DeclIsFromPCHWithObjectFile(const Decl *D) override;
-
   /// Retrieve the module file with a given local ID within the specified
   /// ModuleFile.
   ModuleFile *getLocalModuleFile(ModuleFile &M, unsigned ID);

diff --git a/clang/include/clang/Serialization/ModuleFile.h b/clang/include/clang/Serialization/ModuleFile.h
@@ -155,9 +155,6 @@ class ModuleFile {
   /// Whether timestamps are included in this module file.
   bool HasTimestamps = false;
 
-  /// Whether the PCH has a corresponding object file.
-  bool PCHHasObjectFile = false;
-
   /// Whether the top-level module has been read from the AST file.
   bool DidReadTopLevelSubmodule = false;
 

diff --git a/clang/lib/AST/ASTContext.cpp b/clang/lib/AST/ASTContext.cpp
@@ -10473,37 +10473,6 @@ bool ASTContext::DeclMustBeEmitted(const Decl *D) {
   else
     return false;
 
-  if (D->isFromASTFile() && !LangOpts.BuildingPCHWithObjectFile) {
-    assert(getExternalSource() && "It's from an AST file; must have a source.");
-    // On Windows, PCH files are built together with an object file. If this
-    // declaration comes from such a PCH and DeclMustBeEmitted would return
-    // true, it would have returned true and the decl would have been emitted
-    // into that object file, so it doesn't need to be emitted here.
-    // Note that decls are still emitted if they're referenced, as usual;
-    // DeclMustBeEmitted is used to decide whether a decl must be emitted even
-    // if it's not referenced.
-    //
-    // Explicit template instantiation definitions are tricky. If there was an
-    // explicit template instantiation decl in the PCH before, it will look like
-    // the definition comes from there, even if that was just the declaration.
-    // (Explicit instantiation defs of variable templates always get emitted.)
-    bool IsExpInstDef =
-        isa<FunctionDecl>(D) &&
-        cast<FunctionDecl>(D)->getTemplateSpecializationKind() ==
-            TSK_ExplicitInstantiationDefinition;
-
-    // Implicit member function definitions, such as operator= might not be
-    // marked as template specializations, since they're not coming from a
-    // template but synthesized directly on the class.
-    IsExpInstDef |=
-        isa<CXXMethodDecl>(D) &&
-        cast<CXXMethodDecl>(D)->getParent()->getTemplateSpecializationKind() ==
-            TSK_ExplicitInstantiationDefinition;
-
-    if (getExternalSource()->DeclIsFromPCHWithObjectFile(D) && !IsExpInstDef)
-      return false;
-  }
-
   // If this is a member of a class template, we do not need to emit it.
   if (D->getDeclContext()->isDependentContext())
     return false;

diff --git a/clang/lib/Sema/MultiplexExternalSemaSource.cpp b/clang/lib/Sema/MultiplexExternalSemaSource.cpp
@@ -172,13 +172,6 @@ Module *MultiplexExternalSemaSource::getModule(unsigned ID) {
   return nullptr;
 }
 
-bool MultiplexExternalSemaSource::DeclIsFromPCHWithObjectFile(const Decl *D) {
-  for (auto *S : Sources)
-    if (S->DeclIsFromPCHWithObjectFile(D))
-      return true;
-  return false;
-}
-
 bool MultiplexExternalSemaSource::layoutRecordType(const RecordDecl *Record,
                                                    uint64_t &Size,
                                                    uint64_t &Alignment,

diff --git a/clang/lib/Serialization/ASTReader.cpp b/clang/lib/Serialization/ASTReader.cpp
@@ -2747,7 +2747,7 @@ ASTReader::ReadControlBlock(ModuleFile &F,
         return VersionMismatch;
       }
 
-      bool hasErrors = Record[7];
+      bool hasErrors = Record[6];
       if (hasErrors && !DisableValidation && !AllowASTWithCompilerErrors) {
         Diag(diag::err_pch_with_compiler_errors);
         return HadErrors;
@@ -2765,8 +2765,6 @@ ASTReader::ReadControlBlock(ModuleFile &F,
 
       F.HasTimestamps = Record[5];
 
-      F.PCHHasObjectFile = Record[6];
-
       const std::string &CurBranch = getClangFullRepositoryVersion();
       StringRef ASTBranch = Blob;
       if (StringRef(CurBranch) != ASTBranch && !DisableValidation) {
@@ -8590,11 +8588,6 @@ Module *ASTReader::getModule(unsigned ID) {
   return getSubmodule(ID);
 }
 
-bool ASTReader::DeclIsFromPCHWithObjectFile(const Decl *D) {
-  ModuleFile *MF = getOwningModuleFile(D);
-  return MF && MF->PCHHasObjectFile;
-}
-
 ModuleFile *ASTReader::getLocalModuleFile(ModuleFile &F, unsigned ID) {
   if (ID & 1) {
     // It's a module, look it up by submodule ID.

diff --git a/clang/lib/Serialization/ASTReaderDecl.cpp b/clang/lib/Serialization/ASTReaderDecl.cpp
@@ -504,10 +504,9 @@ uint64_t ASTDeclReader::GetCurrentCursorOffset() {
 
 void ASTDeclReader::ReadFunctionDefinition(FunctionDecl *FD) {
   if (Record.readInt()) {
-    Reader.DefinitionSource[FD] = Loc.F->Kind == ModuleKind::MK_MainFile;
-    if (Reader.getContext().getLangOpts().BuildingPCHWithObjectFile &&
-        Reader.DeclIsFromPCHWithObjectFile(FD))
-      Reader.DefinitionSource[FD] = true;
+    Reader.DefinitionSource[FD] =
+        Loc.F->Kind == ModuleKind::MK_MainFile ||
+        Reader.getContext().getLangOpts().BuildingPCHWithObjectFile;
   }
   if (auto *CD = dyn_cast<CXXConstructorDecl>(FD)) {
     CD->setNumCtorInitializers(Record.readInt());
@@ -1436,10 +1435,9 @@ ASTDeclReader::RedeclarableResult ASTDeclReader::VisitVarDeclImpl(VarDecl *VD) {
   }
 
   if (VD->getStorageDuration() == SD_Static && Record.readInt()) {
-    Reader.DefinitionSource[VD] = Loc.F->Kind == ModuleKind::MK_MainFile;
-    if (Reader.getContext().getLangOpts().BuildingPCHWithObjectFile &&
-        Reader.DeclIsFromPCHWithObjectFile(VD))
-      Reader.DefinitionSource[VD] = true;
+    Reader.DefinitionSource[VD] =
+        Loc.F->Kind == ModuleKind::MK_MainFile ||
+        Reader.getContext().getLangOpts().BuildingPCHWithObjectFile;
   }
 
   enum VarKind {
@@ -1700,10 +1698,9 @@ void ASTDeclReader::ReadCXXDefinitionData(
   Data.HasODRHash = true;
 
   if (Record.readInt()) {
-    Reader.DefinitionSource[D] = Loc.F->Kind == ModuleKind::MK_MainFile;
-    if (Reader.getContext().getLangOpts().BuildingPCHWithObjectFile &&
-        Reader.DeclIsFromPCHWithObjectFile(D))
-      Reader.DefinitionSource[D] = true;
+    Reader.DefinitionSource[D] = 
+        Loc.F->Kind == ModuleKind::MK_MainFile ||
+        Reader.getContext().getLangOpts().BuildingPCHWithObjectFile;
   }
 
   Data.NumBases = Record.readInt();

diff --git a/clang/lib/Serialization/ASTWriter.cpp b/clang/lib/Serialization/ASTWriter.cpp
@@ -1119,7 +1119,6 @@ void ASTWriter::WriteControlBlock(Preprocessor &PP, ASTContext &Context,
   MetadataAbbrev->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 16)); // Clang min.
   MetadataAbbrev->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 1)); // Relocatable
   MetadataAbbrev->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 1)); // Timestamps
-  MetadataAbbrev->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 1)); // PCHHasObjectFile
   MetadataAbbrev->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 1)); // Errors
   MetadataAbbrev->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Blob)); // SVN branch/tag
   unsigned MetadataAbbrevCode = Stream.EmitAbbrev(std::move(MetadataAbbrev));
@@ -1134,7 +1133,6 @@ void ASTWriter::WriteControlBlock(Preprocessor &PP, ASTContext &Context,
         CLANG_VERSION_MINOR,
         !isysroot.empty(),
         IncludeTimestamps,
-        Context.getLangOpts().BuildingPCHWithObjectFile,
         ASTHasCompilerErrors};
     Stream.EmitRecordWithBlob(MetadataAbbrevCode, Record,
                               getClangFullRepositoryVersion());

diff --git a/clang/lib/Serialization/ASTWriterDecl.cpp b/clang/lib/Serialization/ASTWriterDecl.cpp
@@ -1031,8 +1031,10 @@ void ASTDeclWriter::VisitVarDecl(VarDecl *D) {
       // that module interface unit, not by its users. (Inline variables are
       // still emitted in module users.)
       ModulesCodegen =
-          (Writer.WritingModule->Kind == Module::ModuleInterfaceUnit &&
-           Writer.Context->GetGVALinkageForVariable(D) == GVA_StrongExternal);
+          (Writer.WritingModule->Kind == Module::ModuleInterfaceUnit ||
+           (D->hasAttr<DLLExportAttr>() &&
+            Writer.Context->getLangOpts().BuildingPCHWithObjectFile)) &&
+          Writer.Context->GetGVALinkageForVariable(D) == GVA_StrongExternal;
     }
     Record.push_back(ModulesCodegen);
     if (ModulesCodegen)
@@ -2469,7 +2471,10 @@ void ASTRecordWriter::AddFunctionDefinition(const FunctionDecl *FD) {
       Linkage = Writer->Context->GetGVALinkageForFunction(FD);
       ModulesCodegen = *Linkage == GVA_StrongExternal;
     }
-    if (Writer->Context->getLangOpts().ModulesCodegen) {
+    if (Writer->Context->getLangOpts().ModulesCodegen ||
+        (FD->hasAttr<DLLExportAttr>() &&
+         Writer->Context->getLangOpts().BuildingPCHWithObjectFile)) {
+
       // Under -fmodules-codegen, codegen is performed for all non-internal,
       // non-always_inline functions, unless they are available elsewhere.
       if (!FD->hasAttr<AlwaysInlineAttr>()) {

diff --git a/clang/test/CodeGen/builtins-ppc-p10vector.c b/clang/test/CodeGen/builtins-ppc-p10vector.c
@@ -583,13 +583,13 @@ vector float test_vec_vec_splati_ins_f(void) {
 }
 
 int test_vec_test_lsbb_all_ones(void) {
-  // CHECK: @llvm.ppc.vsx.xvtlsbb(<16 x i8> %{{.+}}, i1 true
+  // CHECK: @llvm.ppc.vsx.xvtlsbb(<16 x i8> %{{.+}}, i32 1
   // CHECK-NEXT: ret i32
   return vec_test_lsbb_all_ones(vuca);
 }
 
 int test_vec_test_lsbb_all_zeros(void) {
-  // CHECK: @llvm.ppc.vsx.xvtlsbb(<16 x i8> %{{.+}}, i1 false
+  // CHECK: @llvm.ppc.vsx.xvtlsbb(<16 x i8> %{{.+}}, i32 0
   // CHECK-NEXT: ret i32
   return vec_test_lsbb_all_zeros(vuca);
 }
diff --git a/clang/test/CodeGen/pch-dllexport.cpp b/clang/test/CodeGen/pch-dllexport.cpp
@@ -3,13 +3,20 @@
 // RUN: %clang_cc1 -triple i686-pc-win32 -fms-extensions -emit-obj -emit-llvm -include-pch %t -o - %s | FileCheck -check-prefix=PCH %s
 
 // Build PCH with object file, then use it.
-// RUN: %clang_cc1 -triple i686-pc-win32 -fms-extensions -emit-pch -building-pch-with-obj -o %t %s
-// RUN: %clang_cc1 -triple i686-pc-win32 -fms-extensions -emit-obj -emit-llvm -include-pch %t -building-pch-with-obj -o - %s | FileCheck -check-prefix=OBJ %s
-// RUN: %clang_cc1 -triple i686-pc-win32 -fms-extensions -emit-obj -emit-llvm -include-pch %t -o - %s | FileCheck -check-prefix=PCHWITHOBJ %s
+// RUN: %clang_cc1 -triple i686-pc-win32 -O1 -fms-extensions -emit-pch -building-pch-with-obj -o %t %s
+// RUN: %clang_cc1 -triple i686-pc-win32 -O1 -disable-llvm-optzns -fms-extensions -emit-obj -emit-llvm -include-pch %t -building-pch-with-obj -o - %s | FileCheck -check-prefix=OBJ %s
+// RUN: %clang_cc1 -triple i686-pc-win32 -O1 -disable-llvm-optzns -fms-extensions -emit-obj -emit-llvm -include-pch %t -o - %s | FileCheck -check-prefix=PCHWITHOBJ -check-prefix=PCHWITHOBJ-O1 %s
 
 // Check for vars separately to avoid having to reorder the check statements.
+// RUN: %clang_cc1 -triple i686-pc-win32 -O1 -disable-llvm-optzns -fms-extensions -emit-obj -emit-llvm -include-pch %t -o - %s | FileCheck -check-prefix=PCHWITHOBJVARS %s
+
+// Test the PCHWITHOBJ at -O0 where available_externally definitions are not
+// provided:
+// RUN: %clang_cc1 -triple i686-pc-win32 -fms-extensions -emit-pch -building-pch-with-obj -o %t %s
+// RUN: %clang_cc1 -triple i686-pc-win32 -fms-extensions -emit-obj -emit-llvm -include-pch %t -o - %s | FileCheck -check-prefix=PCHWITHOBJ -check-prefix=PCHWITHOBJ-O0 %s
 // RUN: %clang_cc1 -triple i686-pc-win32 -fms-extensions -emit-obj -emit-llvm -include-pch %t -o - %s | FileCheck -check-prefix=PCHWITHOBJVARS %s
 
+
 #ifndef IN_HEADER
 #define IN_HEADER
 
@@ -23,7 +30,8 @@ inline void __declspec(dllexport) foo() {}
 inline void __declspec(dllexport) baz() {}
 // OBJ: define weak_odr dso_local dllexport void @"?baz@@YAXXZ"
 // PCH: define weak_odr dso_local dllexport void @"?baz@@YAXXZ"
-// PCHWITHOBJ: define weak_odr dso_local dllexport void @"?baz@@YAXXZ"
+// PCHWITHOBJ-O1: define available_externally dso_local void @"?baz@@YAXXZ"
+// PCHWITHOBJ-O0-NOT: define {{.*}}"?baz@@YAXXZ"
 
 
 struct __declspec(dllexport) S {

diff --git a/clang/tools/scan-build-py/tests/functional/exec/CMakeLists.txt b/clang/tools/scan-build-py/tests/functional/exec/CMakeLists.txt
@@ -1,6 +1,6 @@
 project(exec C)
 
-cmake_minimum_required(VERSION 3.4.3)
+cmake_minimum_required(VERSION 3.13.4)
 
 include(CheckCCompilerFlag)
 check_c_compiler_flag("-std=c99" C99_SUPPORTED)

diff --git a/clang/unittests/CMakeLists.txt b/clang/unittests/CMakeLists.txt
@@ -10,10 +10,6 @@ if(CLANG_BUILT_STANDALONE)
   endif()
 endif()
 
-if (CXX_SUPPORTS_SUGGEST_OVERRIDE_FLAG)
-  add_definitions("-Wno-suggest-override")
-endif()
-
 # add_clang_unittest(test_dirname file1.cpp file2.cpp)
 #
 # Will compile the list of files together and link against the clang

diff --git a/compiler-rt/CMakeLists.txt b/compiler-rt/CMakeLists.txt
@@ -3,7 +3,7 @@
 # An important constraint of the build is that it only produces libraries
 # based on the ability of the host toolchain to target various platforms.
 
-cmake_minimum_required(VERSION 3.4.3)
+cmake_minimum_required(VERSION 3.13.4)
 
 if(POLICY CMP0075)
   cmake_policy(SET CMP0075 NEW)

diff --git a/compiler-rt/cmake/Modules/AddCompilerRT.cmake b/compiler-rt/cmake/Modules/AddCompilerRT.cmake
@@ -403,7 +403,6 @@ set(COMPILER_RT_GMOCK_CFLAGS
 
 append_list_if(COMPILER_RT_DEBUG -DSANITIZER_DEBUG=1 COMPILER_RT_UNITTEST_CFLAGS)
 append_list_if(COMPILER_RT_HAS_WCOVERED_SWITCH_DEFAULT_FLAG -Wno-covered-switch-default COMPILER_RT_UNITTEST_CFLAGS)
-append_list_if(COMPILER_RT_HAS_WSUGGEST_OVERRIDE_FLAG -Wno-suggest-override COMPILER_RT_UNITTEST_CFLAGS)
 
 if(MSVC)
   # gtest use a lot of stuff marked as deprecated on Windows.

diff --git a/compiler-rt/cmake/Modules/CustomLibcxx/CMakeLists.txt b/compiler-rt/cmake/Modules/CustomLibcxx/CMakeLists.txt
@@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 3.4.3)
+cmake_minimum_required(VERSION 3.13.4)
 project(custom-libcxx C CXX)
 
 # Build static libcxxabi.

diff --git a/compiler-rt/cmake/config-ix.cmake b/compiler-rt/cmake/config-ix.cmake
@@ -106,7 +106,6 @@ check_cxx_compiler_flag("-Werror -Wnon-virtual-dtor"   COMPILER_RT_HAS_WNON_VIRT
 check_cxx_compiler_flag("-Werror -Wvariadic-macros"    COMPILER_RT_HAS_WVARIADIC_MACROS_FLAG)
 check_cxx_compiler_flag("-Werror -Wunused-parameter"   COMPILER_RT_HAS_WUNUSED_PARAMETER_FLAG)
 check_cxx_compiler_flag("-Werror -Wcovered-switch-default" COMPILER_RT_HAS_WCOVERED_SWITCH_DEFAULT_FLAG)
-check_cxx_compiler_flag("-Werror -Wsuggest-override"   COMPILER_RT_HAS_WSUGGEST_OVERRIDE_FLAG)
 check_cxx_compiler_flag(-Wno-pedantic COMPILER_RT_HAS_WNO_PEDANTIC)
 
 check_cxx_compiler_flag(/W4 COMPILER_RT_HAS_W4_FLAG)

diff --git a/compiler-rt/lib/builtins/CMakeLists.txt b/compiler-rt/lib/builtins/CMakeLists.txt
@@ -3,7 +3,7 @@
 # architecture-specific code in various subdirectories.
 
 if (CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR)
-  cmake_minimum_required(VERSION 3.4.3)
+  cmake_minimum_required(VERSION 3.13.4)
 
   project(CompilerRTBuiltins C ASM)
   set(COMPILER_RT_STANDALONE_BUILD TRUE)

diff --git a/flang/CMakeLists.txt b/flang/CMakeLists.txt
@@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 3.9.0)
+cmake_minimum_required(VERSION 3.13.4)
 
 # RPATH settings on macOS do not affect INSTALL_NAME.
 if (POLICY CMP0068)

diff --git a/flang/lib/Evaluate/constant.cpp b/flang/lib/Evaluate/constant.cpp
@@ -244,19 +244,26 @@ std::size_t Constant<Type<TypeCategory::Character, KIND>>::CopyFrom(
     std::size_t count, ConstantSubscripts &resultSubscripts,
     const std::vector<int> *dimOrder) {
   CHECK(length_ == source.length_);
-  std::size_t copied{0};
-  std::size_t elementBytes{length_ * sizeof(decltype(values_[0]))};
-  ConstantSubscripts sourceSubscripts{source.lbounds()};
-  while (copied < count) {
-    auto *dest{&values_.at(SubscriptsToOffset(resultSubscripts) * length_)};
-    const auto *src{&source.values_.at(
-        source.SubscriptsToOffset(sourceSubscripts) * length_)};
-    std::memcpy(dest, src, elementBytes);
-    copied++;
-    source.IncrementSubscripts(sourceSubscripts);
-    IncrementSubscripts(resultSubscripts, dimOrder);
+  if (length_ == 0) {
+    // It's possible that the array of strings consists of all empty strings.
+    // If so, constant folding will result in a string that's completely empty
+    // and the length_ will be zero, and there's nothing to do.
+    return count;
+  } else {
+    std::size_t copied{0};
+    std::size_t elementBytes{length_ * sizeof(decltype(values_[0]))};
+    ConstantSubscripts sourceSubscripts{source.lbounds()};
+    while (copied < count) {
+      auto *dest{&values_.at(SubscriptsToOffset(resultSubscripts) * length_)};
+      const auto *src{&source.values_.at(
+          source.SubscriptsToOffset(sourceSubscripts) * length_)};
+      std::memcpy(dest, src, elementBytes);
+      copied++;
+      source.IncrementSubscripts(sourceSubscripts);
+      IncrementSubscripts(resultSubscripts, dimOrder);
+    }
+    return copied;
   }
-  return copied;
 }
 
 // Constant<SomeDerived> specialization