[MLIR][mlir-link] Fix conflict resolutions, and add fallback for missing ctors/dtor global symbols (#74)

Author: ex0dus-0x

mlir/include/mlir/Linker/LLVMLinkerMixin.h

@@ -374,6 +374,12 @@ class LLVMLinkerMixin {
       if (srcComdat == mlir::LLVM::comdat::Comdat::NoDeduplicate) {
         return ConflictResolution::Failure;
       }
+      if (srcComdat == mlir::LLVM::comdat::Comdat::ExactMatch) {
+        return ConflictResolution::LinkFromDst;
+      }
+      if (srcComdat == mlir::LLVM::comdat::Comdat::SameSize) {
+        return ConflictResolution::LinkFromDst;
+      }
       llvm_unreachable("unimplemented comdat kind");
     }
 
@@ -384,6 +390,20 @@ class LLVMLinkerMixin {
       return ConflictResolution::Failure;
     }
 
+    if (!srcIsDeclaration && !dstIsDeclaration)
+      return ConflictResolution::Failure;
+
+    if (!srcIsDeclaration && dstIsDeclaration)
+      return ConflictResolution::LinkFromSrc;
+
+    if (srcIsDeclaration && !dstIsDeclaration)
+      return ConflictResolution::LinkFromDst;
+
+    // For same-type linkages not handled above, prefer dst to maintain
+    // stability
+    if (srcLinkage == dstLinkage)
+      return ConflictResolution::LinkFromDst;
+
     llvm_unreachable("unimplemented conflict resolution");
   }
 };

mlir/lib/Dialect/LLVMIR/IR/LLVMLinkerInterface.cpp

@@ -535,8 +535,11 @@ Operation *LLVM::LLVMSymbolLinkerInterface::appendGlobals(llvm::StringRef glob,
     return appendGlobalStructors<LLVM::GlobalDtorsOp>(state);
 
   const auto &globs = append.lookup(glob);
-  if (globs.empty())
+  if (globs.empty()) {
+    if (auto found = summary.find(glob); found != summary.end())
+      return state.clone(found->second);
     return nullptr;
+  }
   if (auto lastGV = dyn_cast<LLVM::GlobalOp>(globs.back()))
     return appendGlobalOps(globs, lastGV, state);
   if (auto comdat = dyn_cast<LLVM::ComdatOp>(globs.back()))