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

[Stephen Tozer via flang-commits]

================
@@ -81,6 +82,8 @@ using namespace Fortran::frontend;
   llvm::PassPluginLibraryInfo get##Ext##PluginInfo();
 #include "llvm/Support/Extension.def"
 
+extern llvm::cl::opt<bool> WriteNewDbgInfoFormat;
----------------
SLTozer wrote:

I _think_ I get the idea, but just to be clear; LLVM flags can influence the output of the clang driver as-is right now, in the sense that LLVM flags control the behaviour of LLVM internal functions, and those functions are invoked by the driver, but there's no direct use of those flags from the driver.

Currently, `--write-experimental-debuginfo` (the flag I added here) influences the output of the clang frontend, because it uses the `PrintModulePass` to print the final LLVM IR. I think the appropriate change to the flang frontend would be to have it do the same, so that there's no behavioural drift between the two - for an action like printing LLVM IR, I think it's probably sensible for both to offload that logic to LLVM's internals.

Does that sound like the right approach to you? Resulting change is something like:
```
@@ -995,6 +995,8 @@ void CodeGenAction::runOptimizationPipeline(llvm::raw_pwrite_stream &os) {

   if (action == BackendActionTy::Backend_EmitBC)
     mpm.addPass(llvm::BitcodeWriterPass(os));
+  else if (action == BackendActionTy::Backend_EmitLL)
+    mpm.addPass(llvm::PrintModulePass(os));

   // Run the passes.
   mpm.run(*llvmModule, mam);
@@ -1270,13 +1272,7 @@ void CodeGenAction::executeAction() {
   // Run LLVM's middle-end (i.e. the optimizer).
   runOptimizationPipeline(ci.isOutputStreamNull() ? *os : ci.getOutputStream());

-  if (action == BackendActionTy::Backend_EmitLL) {
-    llvmModule->print(ci.isOutputStreamNull() ? *os : ci.getOutputStream(),
-                      /*AssemblyAnnotationWriter=*/nullptr);
-    return;
-  }
-
-  if (action == BackendActionTy::Backend_EmitBC) {
+  if (action == BackendActionTy::Backend_EmitLL || action == BackendActionTy::Backend_EmitBC) {
     // This action has effectively been completed in runOptimizationPipeline.
     return;
   }
```

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