[flang-commits] [flang] [mlir] [MLIR][Flang][DebugInfo] Set debug info format in MLIR->IR translation (PR #95098)

[Stephen Tozer via flang-commits]

https://github.com/SLTozer updated https://github.com/llvm/llvm-project/pull/95098

>From 2c84c56b2795cce9afa8ec0b6055aac1ea028331 Mon Sep 17 00:00:00 2001
From: Stephen Tozer <stephen.tozer at sony.com>
Date: Tue, 11 Jun 2024 12:20:31 +0100
Subject: [PATCH 1/2] [MLIR][Flang][DebugInfo] Set debug info format in
 MLIR->IR translation

MLIR's LLVM dialect does not internally support debug records, only
converting to/from debug intrinsics. To smooth the transition from
intrinsics to records, there is a step prior to IR->MLIR translation
that switches the IR module to intrinsic-form; this patch adds the
equivalent conversion to record-form at MLIR->IR translation, and also
modifies the flang front end to use the WriteNewDbgInfoFormat flag when
it is emitting LLVM IR.
---
 flang/lib/Frontend/FrontendActions.cpp       | 7 +++++++
 mlir/lib/Target/LLVMIR/ModuleTranslation.cpp | 5 +++++
 2 files changed, 12 insertions(+)

diff --git a/flang/lib/Frontend/FrontendActions.cpp b/flang/lib/Frontend/FrontendActions.cpp
index b1b6391f1439c..585177b5c7647 100644
--- a/flang/lib/Frontend/FrontendActions.cpp
+++ b/flang/lib/Frontend/FrontendActions.cpp
@@ -50,6 +50,7 @@
 #include "llvm/Analysis/TargetTransformInfo.h"
 #include "llvm/Bitcode/BitcodeWriterPass.h"
 #include "llvm/CodeGen/MachineOptimizationRemarkEmitter.h"
+#include "llvm/IR/DebugProgramInstruction.h"
 #include "llvm/IR/LLVMRemarkStreamer.h"
 #include "llvm/IR/LegacyPassManager.h"
 #include "llvm/IR/Verifier.h"
@@ -81,6 +82,8 @@ using namespace Fortran::frontend;
   llvm::PassPluginLibraryInfo get##Ext##PluginInfo();
 #include "llvm/Support/Extension.def"
 
+extern llvm::cl::opt<bool> WriteNewDbgInfoFormat;
+
 /// Save the given \c mlirModule to a temporary .mlir file, in a location
 /// decided by the -save-temps flag. No files are produced if the flag is not
 /// specified.
@@ -1271,6 +1274,10 @@ void CodeGenAction::executeAction() {
   runOptimizationPipeline(ci.isOutputStreamNull() ? *os : ci.getOutputStream());
 
   if (action == BackendActionTy::Backend_EmitLL) {
+    llvm::ScopedDbgInfoFormatSetter FormatSetter(*llvmModule,
+                                                 WriteNewDbgInfoFormat);
+    if (WriteNewDbgInfoFormat)
+      llvmModule->removeDebugIntrinsicDeclarations();
     llvmModule->print(ci.isOutputStreamNull() ? *os : ci.getOutputStream(),
                       /*AssemblyAnnotationWriter=*/nullptr);
     return;
diff --git a/mlir/lib/Target/LLVMIR/ModuleTranslation.cpp b/mlir/lib/Target/LLVMIR/ModuleTranslation.cpp
index 7b86b250c294b..a5c8c26483edf 100644
--- a/mlir/lib/Target/LLVMIR/ModuleTranslation.cpp
+++ b/mlir/lib/Target/LLVMIR/ModuleTranslation.cpp
@@ -64,6 +64,8 @@ using namespace mlir;
 using namespace mlir::LLVM;
 using namespace mlir::LLVM::detail;
 
+extern llvm::cl::opt<bool> UseNewDbgInfoFormat;
+
 #include "mlir/Dialect/LLVMIR/LLVMConversionEnumsToLLVM.inc"
 
 namespace {
@@ -1789,6 +1791,7 @@ prepareLLVMModule(Operation *m, llvm::LLVMContext &llvmContext,
                   StringRef name) {
   m->getContext()->getOrLoadDialect<LLVM::LLVMDialect>();
   auto llvmModule = std::make_unique<llvm::Module>(name, llvmContext);
+  llvmModule->setNewDbgInfoFormatFlag(false);
   if (auto dataLayoutAttr =
           m->getDiscardableAttr(LLVM::LLVMDialect::getDataLayoutAttrName())) {
     llvmModule->setDataLayout(cast<StringAttr>(dataLayoutAttr).getValue());
@@ -1867,6 +1870,8 @@ mlir::translateModuleToLLVMIR(Operation *module, llvm::LLVMContext &llvmContext,
   if (failed(translator.convertFunctions()))
     return nullptr;
 
+  translator.llvmModule->setIsNewDbgInfoFormat(UseNewDbgInfoFormat);
+
   if (!disableVerification &&
       llvm::verifyModule(*translator.llvmModule, &llvm::errs()))
     return nullptr;

>From 585fca5ff44ddecb2a50eb7e037355ab854bfc6b Mon Sep 17 00:00:00 2001
From: Stephen Tozer <stephen.tozer at sony.com>
Date: Tue, 11 Jun 2024 13:10:03 +0100
Subject: [PATCH 2/2] Add comments for context

---
 flang/lib/Frontend/FrontendActions.cpp       | 2 ++
 mlir/lib/Target/LLVMIR/ModuleTranslation.cpp | 5 +++++
 2 files changed, 7 insertions(+)

diff --git a/flang/lib/Frontend/FrontendActions.cpp b/flang/lib/Frontend/FrontendActions.cpp
index 585177b5c7647..a4db944e8c0ab 100644
--- a/flang/lib/Frontend/FrontendActions.cpp
+++ b/flang/lib/Frontend/FrontendActions.cpp
@@ -1274,6 +1274,8 @@ void CodeGenAction::executeAction() {
   runOptimizationPipeline(ci.isOutputStreamNull() ? *os : ci.getOutputStream());
 
   if (action == BackendActionTy::Backend_EmitLL) {
+    // When printing LLVM IR, we should convert the module to the debug info
+    // format that LLVM expects us to print.
     llvm::ScopedDbgInfoFormatSetter FormatSetter(*llvmModule,
                                                  WriteNewDbgInfoFormat);
     if (WriteNewDbgInfoFormat)
diff --git a/mlir/lib/Target/LLVMIR/ModuleTranslation.cpp b/mlir/lib/Target/LLVMIR/ModuleTranslation.cpp
index a5c8c26483edf..e1a60f195fe89 100644
--- a/mlir/lib/Target/LLVMIR/ModuleTranslation.cpp
+++ b/mlir/lib/Target/LLVMIR/ModuleTranslation.cpp
@@ -1791,6 +1791,8 @@ prepareLLVMModule(Operation *m, llvm::LLVMContext &llvmContext,
                   StringRef name) {
   m->getContext()->getOrLoadDialect<LLVM::LLVMDialect>();
   auto llvmModule = std::make_unique<llvm::Module>(name, llvmContext);
+  // ModuleTranslation can currently only construct modules in the old debug
+  // info format, so set the flag accordingly.
   llvmModule->setNewDbgInfoFormatFlag(false);
   if (auto dataLayoutAttr =
           m->getDiscardableAttr(LLVM::LLVMDialect::getDataLayoutAttrName())) {
@@ -1870,6 +1872,9 @@ mlir::translateModuleToLLVMIR(Operation *module, llvm::LLVMContext &llvmContext,
   if (failed(translator.convertFunctions()))
     return nullptr;
 
+  // Once we've finished constructing elements in the module, we should convert
+  // it to use the debug info format desired by LLVM.
+  // See https://llvm.org/docs/RemoveDIsDebugInfo.html
   translator.llvmModule->setIsNewDbgInfoFormat(UseNewDbgInfoFormat);
 
   if (!disableVerification &&