Introduce new linkage types linkonce_odr, weak_odr, common_odr

and extern_weak_odr.  These are the same as the non-odr versions,
except that they indicate that the global will only be overridden
by an *equivalent* global.  In C, a function with weak linkage can
be overridden by a function which behaves completely differently.
This means that IP passes have to skip weak functions, since any
deductions made from the function definition might be wrong, since
the definition could be replaced by something completely different
at link time.   This is not allowed in C++, thanks to the ODR
(One-Definition-Rule): if a function is replaced by another at
link-time, then the new function must be the same as the original
function.  If a language knows that a function or other global can
only be overridden by an equivalent global, it can give it the
weak_odr linkage type, and the optimizers will understand that it
is alright to make deductions based on the function body.  The
code generators on the other hand map weak and weak_odr linkage
to the same thing.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@66339 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 62 insertions, 22 deletions

diff --git a/include/llvm/GlobalValue.h b/include/llvm/GlobalValue.h
index 8fb5580..33f50c9 100644
--- a/include/llvm/GlobalValue.h
+++ b/include/llvm/GlobalValue.h
@@ -31,16 +31,20 @@ public:
   /// @brief An enumeration for the kinds of linkage for global values.
   enum LinkageTypes {
     ExternalLinkage = 0,///< Externally visible function
-    LinkOnceLinkage,    ///< Keep one copy of function when linking (inline)
-    WeakLinkage,        ///< Keep one copy of named function when linking (weak)
+    LinkOnceAnyLinkage, ///< Keep one copy of function when linking (inline)
+    LinkOnceODRLinkage, ///< Same, but only replaced by something equivalent.
+    WeakAnyLinkage,     ///< Keep one copy of named function when linking (weak)
+    WeakODRLinkage,     ///< Same, but only replaced by something equivalent.
     AppendingLinkage,   ///< Special purpose, only applies to global arrays
     InternalLinkage,    ///< Rename collisions when linking (static functions)
     PrivateLinkage,     ///< Like Internal, but omit from symbol table
     DLLImportLinkage,   ///< Function to be imported from DLL
     DLLExportLinkage,   ///< Function to be accessible from DLL
-    ExternalWeakLinkage,///< ExternalWeak linkage description
+    ExternalWeakAnyLinkage,///< ExternalWeak linkage description
+    ExternalWeakODRLinkage,///< Same, but only replaced by something equivalent.
     GhostLinkage,       ///< Stand-in functions for streaming fns from BC files
-    CommonLinkage       ///< Tentative definitions
+    CommonAnyLinkage,   ///< Tentative definitions
+    CommonODRLinkage    ///< Same, but only replaced by something equivalent.
   };
 
   /// @brief An enumeration for the kinds of visibility of global values.
@@ -99,31 +103,67 @@ public:
     return reinterpret_cast<const PointerType*>(User::getType());
   }
 
-  bool hasExternalLinkage()   const { return Linkage == ExternalLinkage; }
-  bool hasLinkOnceLinkage()   const { return Linkage == LinkOnceLinkage; }
-  bool hasWeakLinkage()       const { return Linkage == WeakLinkage; }
-  bool hasCommonLinkage()     const { return Linkage == CommonLinkage; }
-  bool hasAppendingLinkage()  const { return Linkage == AppendingLinkage; }
-  bool hasInternalLinkage()   const { return Linkage == InternalLinkage; }
-  bool hasPrivateLinkage()    const { return Linkage == PrivateLinkage; }
-  bool hasLocalLinkage()      const {
+  static LinkageTypes getLinkOnceLinkage(bool ODR) {
+    return ODR ? LinkOnceODRLinkage : LinkOnceAnyLinkage;
+  }
+  static LinkageTypes getWeakLinkage(bool ODR) {
+    return ODR ? WeakODRLinkage : WeakAnyLinkage;
+  }
+  static LinkageTypes getCommonLinkage(bool ODR) {
+    return ODR ? CommonODRLinkage : CommonAnyLinkage;
+  }
+  static LinkageTypes getExternalWeakLinkage(bool ODR) {
+    return ODR ? ExternalWeakODRLinkage : ExternalWeakAnyLinkage;
+  }
+
+  bool hasExternalLinkage() const { return Linkage == ExternalLinkage; }
+  bool hasLinkOnceLinkage() const {
+    return Linkage == LinkOnceAnyLinkage || Linkage == LinkOnceODRLinkage;
+  }
+  bool hasWeakLinkage() const {
+    return Linkage == WeakAnyLinkage || Linkage == WeakODRLinkage;
+  }
+  bool hasAppendingLinkage() const { return Linkage == AppendingLinkage; }
+  bool hasInternalLinkage() const { return Linkage == InternalLinkage; }
+  bool hasPrivateLinkage() const { return Linkage == PrivateLinkage; }
+  bool hasLocalLinkage() const {
     return Linkage == InternalLinkage || Linkage == PrivateLinkage;
   }
-  bool hasDLLImportLinkage()  const { return Linkage == DLLImportLinkage; }
-  bool hasDLLExportLinkage()  const { return Linkage == DLLExportLinkage; }
-  bool hasExternalWeakLinkage() const { return Linkage == ExternalWeakLinkage; }
-  bool hasGhostLinkage()      const { return Linkage == GhostLinkage; }
+  bool hasDLLImportLinkage() const { return Linkage == DLLImportLinkage; }
+  bool hasDLLExportLinkage() const { return Linkage == DLLExportLinkage; }
+  bool hasExternalWeakLinkage() const {
+    return Linkage == ExternalWeakAnyLinkage ||
+      Linkage == ExternalWeakODRLinkage;
+  }
+  bool hasGhostLinkage() const { return Linkage == GhostLinkage; }
+  bool hasCommonLinkage() const {
+    return Linkage == CommonAnyLinkage || Linkage == CommonODRLinkage;
+  }
+
   void setLinkage(LinkageTypes LT) { Linkage = LT; }
   LinkageTypes getLinkage() const { return Linkage; }
 
   /// mayBeOverridden - Whether the definition of this global may be replaced
-  /// at link time.  For example, if a function has weak linkage then the code
-  /// defining it may be replaced by different code.
+  /// by something non-equivalent at link time.  For example, if a function has
+  /// weak linkage then the code defining it may be replaced by different code.
   bool mayBeOverridden() const {
-    return (Linkage == WeakLinkage ||
-            Linkage == LinkOnceLinkage ||
-            Linkage == CommonLinkage ||
-            Linkage == ExternalWeakLinkage);
+    return (Linkage == WeakAnyLinkage ||
+            Linkage == LinkOnceAnyLinkage ||
+            Linkage == CommonAnyLinkage ||
+            Linkage == ExternalWeakAnyLinkage);
+  }
+
+  /// isWeakForLinker - Whether the definition of this global may be replaced at
+  /// link time, whether the replacement is equivalent to the original or not.
+  bool isWeakForLinker() const {
+    return (Linkage == WeakAnyLinkage ||
+            Linkage == WeakODRLinkage ||
+            Linkage == LinkOnceAnyLinkage ||
+            Linkage == LinkOnceODRLinkage ||
+            Linkage == CommonAnyLinkage ||
+            Linkage == CommonODRLinkage ||
+            Linkage == ExternalWeakAnyLinkage ||
+            Linkage == ExternalWeakODRLinkage);
   }
 
   /// copyAttributesFrom - copy all additional attributes (those not needed to