Re-apply "[ORC][JITLink] Treat common symbols as weak definitions." with fixes.

This reapplies 785d376, which was reverted in c49837f due to bot
failures. The fix was to relax some asserts to allow common symbols to be
resolved with either common or weak flags, rather than requiring one or the
other.

Author: lhames

llvm/lib/ExecutionEngine/JITLink/COFFLinkGraphBuilder.cpp

@@ -467,7 +467,7 @@ Expected<Symbol *> COFFLinkGraphBuilder::createDefinedSymbol(
     return &G->addDefinedSymbol(
         G->createZeroFillBlock(getCommonSection(), Symbol.getValue(),
                                orc::ExecutorAddr(), Symbol.getValue(), 0),
-        0, SymbolName, Symbol.getValue(), Linkage::Strong, Scope::Default,
+        0, SymbolName, Symbol.getValue(), Linkage::Weak, Scope::Default,
         false, false);
   }
   if (Symbol.isAbsolute())

llvm/lib/ExecutionEngine/JITLink/ELFLinkGraphBuilder.h

@@ -472,7 +472,7 @@ template <typename ELFT> Error ELFLinkGraphBuilder<ELFT>::graphifySymbols() {
       Symbol &GSym = G->addDefinedSymbol(
           G->createZeroFillBlock(getCommonSection(), Sym.st_size,
                                  orc::ExecutorAddr(), Sym.getValue(), 0),
-          0, *Name, Sym.st_size, Linkage::Strong, Scope::Default, false, false);
+          0, *Name, Sym.st_size, Linkage::Weak, Scope::Default, false, false);
       setGraphSymbol(SymIndex, GSym);
       continue;
     }

llvm/lib/ExecutionEngine/JITLink/MachOLinkGraphBuilder.cpp

@@ -366,7 +366,7 @@ Error MachOLinkGraphBuilder::graphifyRegularSymbols() {
                                    orc::ExecutorAddrDiff(NSym.Value),
                                    orc::ExecutorAddr(),
                                    1ull << MachO::GET_COMM_ALIGN(NSym.Desc), 0),
-            0, *NSym.Name, orc::ExecutorAddrDiff(NSym.Value), Linkage::Strong,
+            0, *NSym.Name, orc::ExecutorAddrDiff(NSym.Value), Linkage::Weak,
             NSym.S, false, NSym.Desc & MachO::N_NO_DEAD_STRIP);
       } else {
         if (!NSym.Name)

llvm/lib/ExecutionEngine/Orc/Core.cpp

@@ -932,13 +932,20 @@ Error JITDylib::resolve(MaterializationResponsibility &MR,
           if (SymI->second.getFlags().hasError())
             SymbolsInErrorState.insert(KV.first);
           else {
-            auto Flags = KV.second.getFlags();
-            Flags &= ~JITSymbolFlags::Common;
-            assert(Flags ==
-                       (SymI->second.getFlags() & ~JITSymbolFlags::Common) &&
-                   "Resolved flags should match the declared flags");
+            if (SymI->second.getFlags() & JITSymbolFlags::Common) {
+              auto WeakOrCommon = JITSymbolFlags::Weak | JITSymbolFlags::Common;
+              assert((KV.second.getFlags() & WeakOrCommon) &&
+                     "Common symbols must be resolved as common or weak");
+              assert((KV.second.getFlags() & ~WeakOrCommon) ==
+                         (SymI->second.getFlags() & ~JITSymbolFlags::Common) &&
+                     "Resolving symbol with incorrect flags");
 
-            Worklist.push_back({SymI, {KV.second.getAddress(), Flags}});
+            } else
+              assert(KV.second.getFlags() == SymI->second.getFlags() &&
+                     "Resolved flags should match the declared flags");
+
+            Worklist.push_back(
+                {SymI, {KV.second.getAddress(), SymI->second.getFlags()}});
           }
         }
 
@@ -2899,9 +2906,16 @@ Error ExecutionSession::OL_notifyResolved(MaterializationResponsibility &MR,
            "Resolving symbol outside this responsibility set");
     assert(!I->second.hasMaterializationSideEffectsOnly() &&
            "Can't resolve materialization-side-effects-only symbol");
-    assert((KV.second.getFlags() & ~JITSymbolFlags::Common) ==
-               (I->second & ~JITSymbolFlags::Common) &&
-           "Resolving symbol with incorrect flags");
+    if (I->second & JITSymbolFlags::Common) {
+      auto WeakOrCommon = JITSymbolFlags::Weak | JITSymbolFlags::Common;
+      assert((KV.second.getFlags() & WeakOrCommon) &&
+             "Common symbols must be resolved as common or weak");
+      assert((KV.second.getFlags() & ~WeakOrCommon) ==
+                 (I->second & ~JITSymbolFlags::Common) &&
+             "Resolving symbol with incorrect flags");
+    } else
+      assert(KV.second.getFlags() == I->second &&
+             "Resolving symbol with incorrect flags");
   }
 #endif
 

llvm/test/ExecutionEngine/JITLink/x86-64/COFF_common_symbol.s

@@ -6,7 +6,7 @@
 #
 # CHECK: Creating graph symbols...
 # CHECK:      7: Creating defined graph symbol for COFF symbol "var" in (common) (index: 0)
-# CHECK-NEXT:   0x0 (block + 0x00000000): size: 0x00000004, linkage: strong, scope: default, dead  -   var
+# CHECK-NEXT:   0x0 (block + 0x00000000): size: 0x00000004, linkage: weak, scope: default, dead  -   var
 
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