[ORC] Add weak symbol support to defineMaterializing, fix for PR40074.

The MaterializationResponsibility::defineMaterializing method allows clients to
add new definitions that are in the process of being materialized to the JIT.
This patch adds support to defineMaterializing for symbols with weak linkage
where the new definitions may be rejected if another materializer concurrently
defines the same symbol. If a weak symbol is rejected it will not be added to
the MaterializationResponsibility's responsibility set. Clients can check for
membership in the responsibility set via the
MaterializationResponsibility::getSymbols() method before resolving any
such weak symbols.

This patch also adds code to RTDyldObjectLinkingLayer to tag COFF comdat symbols
introduced during codegen as weak, on the assumption that these are COFF comdat
constants. This fixes http://llvm.org/PR40074.

(cherry picked from commit 84217ad66115cc31b184374a03c8333e4578996f)

1 files changed, 9 insertions, 4 deletions

diff --git a/llvm/include/llvm/ExecutionEngine/Orc/Core.h b/llvm/include/llvm/ExecutionEngine/Orc/Core.h
index d0a9ca5c058..ecba454887b 100644
--- a/llvm/include/llvm/ExecutionEngine/Orc/Core.h
+++ b/llvm/include/llvm/ExecutionEngine/Orc/Core.h
@@ -489,13 +489,18 @@ public:
   /// is guaranteed to return Error::success() and can be wrapped with cantFail.
   Error notifyEmitted();
 
-  /// Adds new symbols to the JITDylib and this responsibility instance.
-  ///        JITDylib entries start out in the materializing state.
+  /// Attempt to claim responsibility for new definitions. This method can be
+  /// used to claim responsibility for symbols that are added to a
+  /// materialization unit during the compilation process (e.g. literal pool
+  /// symbols). Symbol linkage rules are the same as for symbols that are
+  /// defined up front: duplicate strong definitions will result in errors.
+  /// Duplicate weak definitions will be discarded (in which case they will
+  /// not be added to this responsibility instance).
   ///
   ///   This method can be used by materialization units that want to add
   /// additional symbols at materialization time (e.g. stubs, compile
   /// callbacks, metadata).
-  Error defineMaterializing(const SymbolFlagsMap &SymbolFlags);
+  Error defineMaterializing(SymbolFlagsMap SymbolFlags);
 
   /// Notify all not-yet-emitted covered by this MaterializationResponsibility
   /// instance that an error has occurred.
@@ -1023,7 +1028,7 @@ private:
                                        const SymbolStringPtr &DependantName,
                                        MaterializingInfo &EmittedMI);
 
-  Error defineMaterializing(const SymbolFlagsMap &SymbolFlags);
+  Expected<SymbolFlagsMap> defineMaterializing(SymbolFlagsMap SymbolFlags);
 
   void replace(std::unique_ptr<MaterializationUnit> MU);