C++ DR712 and others: handle non-odr-use resulting from an lvalue-to-rvalue conversion applied to a member access or similar not-quite-trivial lvalue expression.

Summary:
When a variable is named in a context where we can't directly emit a
reference to it (because we don't know for sure that it's going to be
defined, or it's from an enclosing function and not captured, or the
reference might not "work" for some reason), we emit a copy of the
variable as a global and use that for the known-to-be-read-only access.

This reinstates r363295, reverted in r363352, with a fix for PR42276:
we now produce a proper name for a non-odr-use reference to a static
constexpr data member. The name <mangled-name>.const is used in that
case; such names are reserved to the implementation for cases such as
this and should demangle nicely.

Reviewers: rjmccall

Subscribers: jdoerfert, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D63157

llvm-svn: 363428

1 files changed, 7 insertions, 0 deletions

diff --git a/clang/lib/CodeGen/CodeGenModule.h b/clang/lib/CodeGen/CodeGenModule.h
index 8c1bc0777de..95964afed4e 100644
--- a/clang/lib/CodeGen/CodeGenModule.h
+++ b/clang/lib/CodeGen/CodeGenModule.h
@@ -362,6 +362,10 @@ 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.
@@ -623,6 +627,9 @@ public:
     StaticLocalDeclGuardMap[D] = C;
   }
 
+  Address createUnnamedGlobalFrom(const VarDecl &D, llvm::Constant *Constant,
+                                  CharUnits Align);
+
   bool lookupRepresentativeDecl(StringRef MangledName,
                                 GlobalDecl &Result) const;