flang][debug] Run AddDebugInfo before TargetRewrite. (#114418)

This help us generate debug info that better represents the actual
Fortran source code. It was briefly discussed
[here](#113917 (review)).
    
Fixes #108711.

Author: abidh

flang/lib/Optimizer/Passes/Pipelines.cpp

@@ -264,10 +264,10 @@ void createDefaultFIRCodeGenPassPipeline(mlir::PassManager &pm,
   addNestedPassToAllTopLevelOperations(pm, fir::createAbstractResultOpt);
   fir::addCodeGenRewritePass(
       pm, (config.DebugInfo != llvm::codegenoptions::NoDebugInfo));
-  fir::addTargetRewritePass(pm);
-  fir::addCompilerGeneratedNamesConversionPass(pm);
   fir::addExternalNameConversionPass(pm, config.Underscoring);
   fir::createDebugPasses(pm, config.DebugInfo, config.OptLevel, inputFilename);
+  fir::addTargetRewritePass(pm);
+  fir::addCompilerGeneratedNamesConversionPass(pm);
 
   if (config.VScaleMin != 0)
     pm.addPass(fir::createVScaleAttr({{config.VScaleMin, config.VScaleMax}}));

flang/test/Driver/mlir-debug-pass-pipeline.f90

@@ -111,10 +111,10 @@
 
 ! ALL-NEXT: CodeGenRewrite
 ! ALL-NEXT:   (S) 0 num-dce'd - Number of operations eliminated
-! ALL-NEXT: TargetRewrite
-! ALL-NEXT: CompilerGeneratedNamesConversion
 ! ALL-NEXT: ExternalNameConversion
 ! DEBUG-NEXT: AddDebugInfo
 ! NO-DEBUG-NOT: AddDebugInfo
+! ALL-NEXT: TargetRewrite
+! ALL-NEXT: CompilerGeneratedNamesConversion
 ! ALL: FIRToLLVMLowering
 ! ALL-NOT: LLVMIRLoweringPass

flang/test/Driver/mlir-pass-pipeline.f90

@@ -120,8 +120,8 @@
 
 ! ALL-NEXT: CodeGenRewrite
 ! ALL-NEXT:   (S) 0 num-dce'd - Number of operations eliminated
+! ALL-NEXT: ExternalNameConversion
 ! ALL-NEXT: TargetRewrite
 ! ALL-NEXT: CompilerGeneratedNamesConversion
-! ALL-NEXT: ExternalNameConversion
 ! ALL-NEXT: FIRToLLVMLowering
 ! ALL-NOT: LLVMIRLoweringPass

flang/test/Integration/debug-complex-2.f90

@@ -0,0 +1,12 @@
+! RUN: %flang_fc1 -emit-llvm -debug-info-kind=standalone %s -o - | FileCheck  %s
+
+! Test that complex return type is correctly represented in debug.
+complex function fn(a)
+    complex, intent(in) :: a
+    fn = a
+end function
+
+! CHECK-DAG: ![[CMPLX:.*]] = !DIBasicType(name: "complex", size: 64, encoding: DW_ATE_complex_float)
+! CHECK-DAG: ![[SR_TY:.*]] = !DISubroutineType(cc: DW_CC_normal, types: ![[TYPES:.*]])
+! CHECK-DAG: ![[TYPES]] = !{![[CMPLX]], ![[CMPLX]]}
+! CHECK-DAG: !DISubprogram(name: "fn"{{.*}}type: ![[SR_TY]]{{.*}})

flang/test/Integration/debug-external-linkage-name.f90

@@ -0,0 +1,10 @@
+! RUN: %flang_fc1 -emit-llvm -debug-info-kind=standalone %s -o - | FileCheck  %s
+
+! Test that correct linkage name is generated in the debug info.
+subroutine sub(a)
+  integer :: a
+  return a+1
+end
+
+!CHECK: !DISubprogram(name: "sub", linkageName: "sub_"{{.*}})
+