[MLIR][mlir-link] Fix alignment and constness setting in conflict resolution (#73)

Fixing up the code to do it the same way as how llvm-link does it.

Author: Jezurko

clang/lib/CIR/Dialect/IR/CIRLinkerInterface.cpp

@@ -177,6 +177,14 @@ class CIRSymbolLinkerInterface
     llvm_unreachable("unexpected operation");
   }
 
+  static void setIsConstant(Operation *op, bool value) {
+    if (auto gv = dyn_cast<cir::GlobalOp>(op))
+      return gv.setConstant(value);
+    llvm_unreachable("constness setting allowed only for globals");
+  }
+
+  static bool isGlobalVar(Operation *op) { return isa<cir::GlobalOp>(op); }
+
   static llvm::StringRef getSection(Operation *op) {
     if (auto gv = dyn_cast<cir::GlobalOp>(op)) {
       auto section = gv.getSection();

mlir/include/mlir/Dialect/LLVMIR/LLVMLinkerInterface.h

@@ -24,6 +24,8 @@ class LLVMSymbolLinkerInterface
   static std::optional<uint64_t> getAlignment(Operation *op);
   static void setAlignment(Operation *op, std::optional<uint64_t>);
   static bool isConstant(Operation *op);
+  static void setIsConstant(Operation *op, bool value);
+  static bool isGlobalVar(Operation *op);
   static llvm::StringRef getSection(Operation *op);
   static uint32_t getAddressSpace(Operation *op);
   StringRef getSymbol(Operation *op) const override;

mlir/include/mlir/Linker/LLVMLinkerMixin.h

@@ -279,13 +279,25 @@ class LLVMLinkerMixin {
     const bool srcIsDeclaration = isDeclarationForLinker(pair.src);
     const bool dstIsDeclaration = isDeclarationForLinker(pair.dst);
 
-    std::optional<uint64_t> srcAlignment = derived.getAlignment(pair.src);
-    std::optional<uint64_t> dstAlignment = derived.getAlignment(pair.dst);
-    std::optional<uint64_t> alignment = std::nullopt;
-    if (srcAlignment || dstAlignment)
-      alignment = std::max(srcAlignment.value_or(1), dstAlignment.value_or(1));
-    derived.setAlignment(pair.src, alignment);
-    derived.setAlignment(pair.dst, alignment);
+    if (!isLocalLinkage(srcLinkage) && !isAppendingLinkage(srcLinkage)) {
+      if (derived.isGlobalVar(pair.src) && derived.isGlobalVar(pair.dst)) {
+        if (srcIsDeclaration && dstIsDeclaration &&
+            (!derived.isConstant(pair.src) || !derived.isConstant(pair.dst))) {
+          derived.setIsConstant(pair.src, false);
+          derived.setIsConstant(pair.dst, false);
+        }
+        if (isCommonLinkage(srcLinkage) && isCommonLinkage(dstLinkage)) {
+          std::optional<uint64_t> srcAlignment = derived.getAlignment(pair.src);
+          std::optional<uint64_t> dstAlignment = derived.getAlignment(pair.dst);
+          std::optional<uint64_t> alignment = std::nullopt;
+          if (srcAlignment || dstAlignment)
+            alignment =
+                std::max(srcAlignment.value_or(1), dstAlignment.value_or(1));
+          derived.setAlignment(pair.src, alignment);
+          derived.setAlignment(pair.dst, alignment);
+        }
+      }
+    }
 
     if (isAppendingLinkage(dstLinkage)) {
       return ConflictResolution::LinkFromSrc;

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

@@ -196,6 +196,18 @@ bool LLVM::LLVMSymbolLinkerInterface::isConstant(Operation *op) {
   llvm_unreachable("unexpected operation");
 }
 
+void LLVM::LLVMSymbolLinkerInterface::setIsConstant(Operation *op, bool value) {
+  if (auto gv = dyn_cast<LLVM::GlobalOp>(op)) {
+    gv.setConstant(value);
+    return;
+  }
+  llvm_unreachable("constness setting allowed only for globals");
+}
+
+bool LLVM::LLVMSymbolLinkerInterface::isGlobalVar(Operation *op) {
+  return isa<LLVM::GlobalOp>(op);
+}
+
 llvm::StringRef LLVM::LLVMSymbolLinkerInterface::getSection(Operation *op) {
   if (auto gv = dyn_cast<LLVM::GlobalOp>(op)) {
     auto section = gv.getSection();