[mlir][LLVMIR] Handle missing functions in CGProfile module flags (#169517)

This commit extends the CGProfile module flags export with support for missing function references. Previously, this caused a crash and now it's properly exported to `null` values in the metadata node.
Fixes: #160717

Author: Men-cotton

mlir/lib/Target/LLVMIR/Dialect/LLVMIR/LLVMToLLVMIRTranslation.cpp

@@ -243,16 +243,16 @@ convertModuleFlagValue(StringRef key, ArrayAttr arrayAttr,
 
   if (key == LLVMDialect::getModuleFlagKeyCGProfileName()) {
     for (auto entry : arrayAttr.getAsRange<ModuleFlagCGProfileEntryAttr>()) {
-      llvm::Metadata *fromMetadata =
-          entry.getFrom()
-              ? llvm::ValueAsMetadata::get(moduleTranslation.lookupFunction(
-                    entry.getFrom().getValue()))
-              : nullptr;
-      llvm::Metadata *toMetadata =
-          entry.getTo()
-              ? llvm::ValueAsMetadata::get(
-                    moduleTranslation.lookupFunction(entry.getTo().getValue()))
-              : nullptr;
+      auto getFuncMetadata = [&](FlatSymbolRefAttr sym) -> llvm::Metadata * {
+        if (!sym)
+          return nullptr;
+        if (llvm::Function *fn =
+                moduleTranslation.lookupFunction(sym.getValue()))
+          return llvm::ValueAsMetadata::get(fn);
+        return nullptr;
+      };
+      llvm::Metadata *fromMetadata = getFuncMetadata(entry.getFrom());
+      llvm::Metadata *toMetadata = getFuncMetadata(entry.getTo());
 
       llvm::Metadata *vals[] = {
           fromMetadata, toMetadata,

mlir/test/Dialect/LLVMIR/invalid-cg-profile.mlir

@@ -0,0 +1,14 @@
+// RUN: mlir-translate %s -mlir-to-llvmir | FileCheck %s
+// CHECK: !llvm.module.flags = !{![[CG_FLAG:[0-9]+]], ![[DBG_FLAG:[0-9]+]]}
+// CHECK: ![[CG_FLAG]] = !{i32 5, !"CG Profile", ![[CG_LIST:[0-9]+]]}
+// CHECK: ![[CG_LIST]] = distinct !{![[CG_ENTRY:[0-9]+]], ![[CG_ENTRY]], ![[CG_ENTRY]]}
+// CHECK: ![[CG_ENTRY]] = !{null, null, i64 222}
+// CHECK: ![[DBG_FLAG]] = !{i32 2, !"Debug Info Version", i32 3}
+
+module {
+  llvm.module_flags [#llvm.mlir.module_flag<append, "CG Profile", [
+                       #llvm.cgprofile_entry<from = @from, to = @to, count = 222>,
+                       #llvm.cgprofile_entry<from = @from, count = 222>,
+                       #llvm.cgprofile_entry<from = @to, to = @from, count = 222>
+                    ]>]
+}