[mlir] Allow setting of Dwarf version information.

The dwarf version to use can be set in the LLVM IR using the
"Dwarf Version" flag. This PR allows setting this flag by using a
new attribute on the module.

Author: abidh

mlir/include/mlir/Dialect/LLVMIR/LLVMDialect.td

@@ -92,6 +92,8 @@ def LLVM_Dialect : Dialect {
     static StringRef getDependentLibrariesAttrName() {
       return "llvm.dependent_libraries";
     }
+    /// Name of the dwarf version attribute.
+    static StringRef getDwarfVersionAttrName() { return "llvm.dwarf_version"; }
 
     /// Names of known llvm module flag keys.
     static StringRef getModuleFlagKeyCGProfileName() {

mlir/lib/Target/LLVMIR/DebugTranslation.cpp

@@ -36,8 +36,9 @@ DebugTranslation::DebugTranslation(Operation *module, llvm::Module &llvmModule)
 
 static constexpr StringRef kDebugVersionKey = "Debug Info Version";
 static constexpr StringRef kCodeViewKey = "CodeView";
+static constexpr StringRef kDwarfVersionKey = "Dwarf Version";
 
-void DebugTranslation::addModuleFlagsIfNotPresent() {
+void DebugTranslation::addModuleFlagsIfNotPresent(Operation *module) {
   // TODO: The version information should be encoded on the LLVM module itself,
   // not implicitly set here.
 
@@ -53,6 +54,13 @@ void DebugTranslation::addModuleFlagsIfNotPresent() {
     if (!llvmModule.getModuleFlag(kCodeViewKey))
       llvmModule.addModuleFlag(llvm::Module::Warning, kCodeViewKey, 1);
   }
+  if (auto attr = module->getAttrOfType<IntegerAttr>(
+          LLVM::LLVMDialect::getDwarfVersionAttrName())) {
+    int32_t attrValue = attr.getInt();
+    assert((attrValue >= 2 && attrValue <= 5) && "Unsupported DWARF version");
+    if (!llvmModule.getModuleFlag(kDwarfVersionKey))
+      llvmModule.addModuleFlag(llvm::Module::Max, kDwarfVersionKey, attrValue);
+  }
 }
 
 /// Translate the debug information for the given function.

mlir/lib/Target/LLVMIR/DebugTranslation.h

@@ -32,7 +32,7 @@ class DebugTranslation {
   DebugTranslation(Operation *module, llvm::Module &llvmModule);
 
   /// Adds the necessary module flags to the module, if not yet present.
-  void addModuleFlagsIfNotPresent();
+  void addModuleFlagsIfNotPresent(Operation *module);
 
   /// Translate the given location to an llvm debug location.
   llvm::DILocation *translateLoc(Location loc, llvm::DILocalScope *scope);

mlir/lib/Target/LLVMIR/ModuleTranslation.cpp

@@ -2418,7 +2418,7 @@ mlir::translateModuleToLLVMIR(Operation *module, llvm::LLVMContext &llvmContext,
 
   // Add the necessary debug info module flags, if they were not encoded in MLIR
   // beforehand.
-  translator.debugTranslation->addModuleFlagsIfNotPresent();
+  translator.debugTranslation->addModuleFlagsIfNotPresent(module);
 
   // Call the OpenMP IR Builder callbacks prior to verifying the module
   if (auto *ompBuilder = translator.getOpenMPBuilder())

mlir/test/Target/LLVMIR/llvmir.mlir

@@ -3040,3 +3040,23 @@ llvm.mlir.global external @target_specific_attrs_only() {target_specific_attrs =
 // CHECK: @target_specific_attrs_combined = global i32 2, section "mysection", align 4 #[[ATTRS:[0-9]+]]
 // CHECK: attributes #[[ATTRS]] = { norecurse "bss-section"="my_bss.1" }
 llvm.mlir.global external @target_specific_attrs_combined(2 : i32) {alignment = 4 : i64, section = "mysection", target_specific_attrs = ["norecurse", ["bss-section", "my_bss.1"]]} : i32
+
+// -----
+
+module attributes {llvm.dwarf_version = 5 : i32} {}
+// CHECK: !{i32 7, !"Dwarf Version", i32 5}
+
+// -----
+
+module attributes {llvm.dwarf_version = 4 : i32} {}
+// CHECK: !{i32 7, !"Dwarf Version", i32 4}
+
+// -----
+
+module attributes {llvm.dwarf_version = 3 : i32} {}
+// CHECK: !{i32 7, !"Dwarf Version", i32 3}
+
+// -----
+
+module attributes {llvm.dwarf_version = 2 : i32} {}
+// CHECK: !{i32 7, !"Dwarf Version", i32 2}