[mlir] Always create a list of alias scopes when emitting LLVM IR

[ftynse]

Summary

Previously, the translation to LLVM IR would emit IR that directly uses
a scope metadata node in case only one scope was in use in alias.scopes
or noalias metadata. It should always be a list of scopes. The verifier
change in 8700f2bd36bb9b7d7075ed4dac0aef92b9489237 enforced this and
broke the test. Fix the translation to always create a list of scopes
using a new metadata node, update and reenable the respective test.

Fixes PR51919.

[mehdi_amini]

Thanks!

Can you cross-check with https://reviews.llvm.org/D110189 ? I think you have the same fix but the test update is slightly different.

[ftynse]

Yeah, the change is the same and the matcher differs only by variable names.

mlir/lib/Target/LLVMIR/ModuleTranslation.cpp

auto populateScopeMetadata = [this, op, inst](StringRef attrName,
                                                 StringRef llvmMetadataName) {
     auto scopes = op->getAttrOfType<ArrayAttr>(attrName);
     if (!scopes || scopes.empty())
       return;
     llvm::Module *module = inst->getModule();
     SmallVector<llvm::Metadata *> scopeMDs;
     for (SymbolRefAttr scopeRef : scopes.getAsRange<SymbolRefAttr>())
       scopeMDs.push_back(getAliasScope(*op, scopeRef));
-    llvm::MDNode *unionMD = nullptr;
-    if (scopeMDs.size() == 1)
-      unionMD = llvm::cast<llvm::MDNode>(scopeMDs.front());
-    else if (scopeMDs.size() >= 2)
-      unionMD = llvm::MDNode::get(module->getContext(), scopeMDs);
+    llvm::MDNode *unionMD = llvm::MDNode::get(module->getContext(), scopeMDs);
     inst->setMetadata(module->getMDKindID(llvmMetadataName), unionMD);
   };
 
   populateScopeMetadata(LLVMDialect::getAliasScopesAttrName(), "alias.scope");
   populateScopeMetadata(LLVMDialect::getNoAliasScopesAttrName(), "noalias");
 }
 
 llvm::Type *ModuleTranslation::convertType(Type type) {

mlir/test/Target/LLVMIR/llvmir.mlir

 // RUN: mlir-translate -mlir-to-llvmir -split-input-file %s | FileCheck %s
-// This is failing the LLVM verifier after 8700f2bd36bb9b
-// XFAIL: *
 
 // CHECK: @global_aligned32 = private global i64 42, align 32
 "llvm.mlir.global"() ({}) {sym_name = "global_aligned32", type = i64, value = 42 : i64, linkage = #llvm.linkage<private>, alignment = 32} : () -> ()
 
 // CHECK: @global_aligned64 = private global i64 42, align 64
 llvm.mlir.global private @global_aligned64(42 : i64) {alignment = 64 : i64} : i64
 
 // CHECK: @global_aligned64_native = private global i64 42, align 64
llvm.metadata @metadata {
     llvm.alias_scope @scope2 { domain = @domain }
     llvm.alias_scope @scope3 { domain = @domain }
     llvm.return
   }
 }
 
 // Function
 // CHECK-LABEL: aliasScope
-// CHECK:  store {{.*}}, !alias.scope ![[SCOPE1:[0-9]+]], !noalias ![[SCOPES23:[0-9]+]]
-// CHECK:  store {{.*}}, !alias.scope ![[SCOPE2:[0-9]+]], !noalias ![[SCOPES13:[0-9]+]]
-// CHECK:  load {{.*}},  !alias.scope ![[SCOPE3:[0-9]+]], !noalias ![[SCOPES12:[0-9]+]]
+// CHECK:  store {{.*}}, !alias.scope ![[SCOPES1:[0-9]+]], !noalias ![[SCOPES23:[0-9]+]]
+// CHECK:  store {{.*}}, !alias.scope ![[SCOPES2:[0-9]+]], !noalias ![[SCOPES13:[0-9]+]]
+// CHECK:  load {{.*}},  !alias.scope ![[SCOPES3:[0-9]+]], !noalias ![[SCOPES12:[0-9]+]]
 
 // Metadata
 // CHECK-DAG: ![[DOMAIN:[0-9]+]] = distinct !{![[DOMAIN]], !"The domain"}
-// CHECK-DAG: ![[SCOPE1]] = distinct !{![[SCOPE1]], ![[DOMAIN]], !"The first scope"}
-// CHECK-DAG: ![[SCOPE2]] = distinct !{![[SCOPE2]], ![[DOMAIN]]}
-// CHECK-DAG: ![[SCOPE3]] = distinct !{![[SCOPE3]], ![[DOMAIN]]}
+// CHECK-DAG: ![[SCOPE1:[0-9]+]] = distinct !{![[SCOPE1]], ![[DOMAIN]], !"The first scope"}
+// CHECK-DAG: ![[SCOPE2:[0-9]+]] = distinct !{![[SCOPE2]], ![[DOMAIN]]}
+// CHECK-DAG: ![[SCOPE3:[0-9]+]] = distinct !{![[SCOPE3]], ![[DOMAIN]]}
+// CHECK-DAG: ![[SCOPES1]] = !{![[SCOPE1]]}
+// CHECK-DAG: ![[SCOPES2]] = !{![[SCOPE2]]}
+// CHECK-DAG: ![[SCOPES3]] = !{![[SCOPE3]]}
 // CHECK-DAG: ![[SCOPES12]] = !{![[SCOPE1]], ![[SCOPE2]]}
 // CHECK-DAG: ![[SCOPES13]] = !{![[SCOPE1]], ![[SCOPE3]]}
 // CHECK-DAG: ![[SCOPES23]] = !{![[SCOPE2]], ![[SCOPE3]]}