[MLIR][LLVM] Enable export of DISubprograms on function declarations (#78026)

This commit changes the MLIR to LLVMIR export to also attach subprogram
debug attachements to function declarations.
This commit additonally fixes the two passes that produce subprograms to
not attach the "Definition" flag to function declarations. This
otherwise results in invalid LLVM IR.

Author: Dinistro

flang/lib/Optimizer/Transforms/AddDebugFoundation.cpp

@@ -97,16 +97,18 @@ void AddDebugFoundationPass::runOnOperation() {
     // Only definitions need a distinct identifier and a compilation unit.
     mlir::DistinctAttr id;
     mlir::LLVM::DICompileUnitAttr compilationUnit;
+    auto subprogramFlags = mlir::LLVM::DISubprogramFlags::Optimized;
     if (!funcOp.isExternal()) {
       id = mlir::DistinctAttr::create(mlir::UnitAttr::get(context));
       compilationUnit = cuAttr;
+      subprogramFlags =
+          subprogramFlags | mlir::LLVM::DISubprogramFlags::Definition;
     }
-    mlir::LLVM::DISubprogramAttr spAttr = mlir::LLVM::DISubprogramAttr::get(
+    auto spAttr = mlir::LLVM::DISubprogramAttr::get(
         context, id, compilationUnit, fileAttr, funcName, funcName,
         funcFileAttr,
         /*line=*/1,
-        /*scopeline=*/1, mlir::LLVM::DISubprogramFlags::Definition,
-        subTypeAttr);
+        /*scopeline=*/1, subprogramFlags, subTypeAttr);
     funcOp->setLoc(builder.getFusedLoc({funcOp->getLoc()}, spAttr));
   });
 }

flang/test/Transforms/debug-line-table.fir

@@ -24,7 +24,7 @@ module attributes { fir.defaultkind = "a1c4d8i4l4r4", fir.kindmap = "", llvm.dat
 // CHECK: #[[DECL_LOC:.*]] = loc("./simple.f90":10:1)
 // CHECK: #di_compile_unit = #llvm.di_compile_unit<id = distinct[{{.*}}]<>, sourceLanguage = DW_LANG_Fortran95, file = #di_file, producer = "Flang", isOptimized = false, emissionKind = LineTablesOnly>
 // CHECK: #di_subroutine_type = #llvm.di_subroutine_type<callingConvention = DW_CC_normal, types = #di_basic_type, #di_basic_type>
-// CHECK: #[[SB_SUBPROGRAM:.*]] = #llvm.di_subprogram<id = distinct[{{.*}}]<>, compileUnit = #di_compile_unit, scope = #di_file, name = "[[SB_NAME]]", linkageName = "[[SB_NAME]]", file = #di_file, line = 1, scopeLine = 1, subprogramFlags = Definition, type = #di_subroutine_type>
-// CHECK: #[[DECL_SUBPROGRAM:.*]] = #llvm.di_subprogram<scope = #di_file, name = "[[DECL_NAME]]", linkageName = "[[DECL_NAME]]", file = #di_file, line = 1, scopeLine = 1, subprogramFlags = Definition, type = #di_subroutine_type>
+// CHECK: #[[SB_SUBPROGRAM:.*]] = #llvm.di_subprogram<id = distinct[{{.*}}]<>, compileUnit = #di_compile_unit, scope = #di_file, name = "[[SB_NAME]]", linkageName = "[[SB_NAME]]", file = #di_file, line = 1, scopeLine = 1, subprogramFlags = "Definition|Optimized", type = #di_subroutine_type>
+// CHECK: #[[DECL_SUBPROGRAM:.*]] = #llvm.di_subprogram<scope = #di_file, name = "[[DECL_NAME]]", linkageName = "[[DECL_NAME]]", file = #di_file, line = 1, scopeLine = 1, subprogramFlags = Optimized, type = #di_subroutine_type>
 // CHECK: #[[FUSED_SB_LOC]] = loc(fused<#[[SB_SUBPROGRAM]]>[#[[SB_LOC]]])
 // CHECK: #[[FUSED_DECL_LOC]] = loc(fused<#[[DECL_SUBPROGRAM]]>[#[[DECL_LOC]]])

mlir/lib/Dialect/LLVMIR/Transforms/DIScopeForLLVMFuncOp.cpp

@@ -67,18 +67,19 @@ static void addScopeToFunction(LLVM::LLVMFuncOp llvmFunc,
 
   StringAttr funcNameAttr = llvmFunc.getNameAttr();
   // Only definitions need a distinct identifier and a compilation unit.
-  mlir::DistinctAttr id;
-  if (!llvmFunc.isExternal())
+  DistinctAttr id;
+  auto subprogramFlags = LLVM::DISubprogramFlags::Optimized;
+  if (!llvmFunc.isExternal()) {
     id = mlir::DistinctAttr::create(mlir::UnitAttr::get(context));
-  else
+    subprogramFlags = subprogramFlags | LLVM::DISubprogramFlags::Definition;
+  } else {
     compileUnitAttr = {};
-  mlir::LLVM::DISubprogramAttr subprogramAttr = LLVM::DISubprogramAttr::get(
+  }
+  auto subprogramAttr = LLVM::DISubprogramAttr::get(
       context, id, compileUnitAttr, fileAttr, funcNameAttr, funcNameAttr,
       fileAttr,
       /*line=*/line,
-      /*scopeline=*/col,
-      LLVM::DISubprogramFlags::Definition | LLVM::DISubprogramFlags::Optimized,
-      subroutineTypeAttr);
+      /*scopeline=*/col, subprogramFlags, subroutineTypeAttr);
   llvmFunc->setLoc(FusedLoc::get(context, {loc}, subprogramAttr));
 }
 

mlir/lib/Target/LLVMIR/ModuleTranslation.cpp

@@ -1074,9 +1074,6 @@ LogicalResult ModuleTranslation::convertOneFunction(LLVMFuncOp func) {
   branchMapping.clear();
   llvm::Function *llvmFunc = lookupFunction(func.getName());
 
-  // Translate the debug information for this function.
-  debugTranslation->translate(func, *llvmFunc);
-
   // Add function arguments to the value remapping table.
   for (auto [mlirArg, llvmArg] :
        llvm::zip(func.getArguments(), llvmFunc->args()))
@@ -1261,6 +1258,9 @@ LogicalResult ModuleTranslation::convertFunctionSignatures() {
 
     if (auto alignment = function.getAlignment())
       llvmFunc->setAlignment(llvm::MaybeAlign(*alignment));
+
+    // Translate the debug information for this function.
+    debugTranslation->translate(function, *llvmFunc);
   }
 
   return success();

mlir/test/Target/LLVMIR/llvmir-debug.mlir

@@ -169,6 +169,20 @@ llvm.func @empty_types() {
 
 // -----
 
+#di_file = #llvm.di_file<"foo.mlir" in "/test/">
+#di_subprogram = #llvm.di_subprogram<
+  scope = #di_file, name = "func_decl_with_subprogram", file = #di_file, subprogramFlags = "Optimized"
+>
+
+// CHECK-LABEL: declare !dbg
+// CHECK-SAME: ![[SUBPROGRAM:.*]] i32 @func_decl_with_subprogram(
+llvm.func @func_decl_with_subprogram() -> (i32) loc(fused<#di_subprogram>["foo.mlir":2:1])
+
+// CHECK: ![[SUBPROGRAM]] = !DISubprogram(name: "func_decl_with_subprogram", scope: ![[FILE:.*]], file: ![[FILE]], spFlags: DISPFlagOptimized)
+// CHECK: ![[FILE]] = !DIFile(filename: "foo.mlir", directory: "/test/")
+
+// -----
+
 #di_basic_type = #llvm.di_basic_type<tag = DW_TAG_base_type, name = "int", sizeInBits = 32, encoding = DW_ATE_signed>
 #di_file = #llvm.di_file<"foo.mlir" in "/test/">
 #di_compile_unit = #llvm.di_compile_unit<