[flang-commits] [flang] dabd9fe - [flang] Attribute the generated entry point to the main program's start (#223742)

[via flang-commits]

Author: jiel-nv
Date: 2026-09-16T10:23:38+01:00
New Revision: dabd9fe738cc20e8f4364c7b07a1f7f45d2a537d

URL: https://github.com/llvm/llvm-project/commit/dabd9fe738cc20e8f4364c7b07a1f7f45d2a537d
DIFF: https://github.com/llvm/llvm-project/commit/dabd9fe738cc20e8f4364c7b07a1f7f45d2a537d.diff

LOG: [flang] Attribute the generated entry point to the main program's start (#223742)

The `main` entry point that lowering generates for a Fortran main
program is attributed to the end-stmt of the last function-like unit
that was lowered. e.g.

```fortran
subroutine foo(x)
  real :: x
  x = x + 1.0
end subroutine foo

program demo
  real :: a
  a = 1.0
  call foo(a)
  print *, a
end program demo
```

`PROGRAM` is on line 6 and `end program` on line 11. 

The loc info shows up in FIR for the compiler generated C `main`
wrapper:

```
before this PR:  } loc("repro.f90":11:1)
after this PR:   } loc("repro.f90":6:1)
```

Added: 
    

Modified: 
    flang/lib/Lower/Bridge.cpp
    flang/test/Lower/main_location.f90

Removed: 
    


################################################################################
diff  --git a/flang/lib/Lower/Bridge.cpp b/flang/lib/Lower/Bridge.cpp
index 099035e91e700..5e9550b3ff215 100644
--- a/flang/lib/Lower/Bridge.cpp
+++ b/flang/lib/Lower/Bridge.cpp
@@ -531,6 +531,7 @@ class FirConverter : public Fortran::lower::AbstractConverter {
     // - Module variables are lowered once all the function declarations are
     // available.
     bool hasMainProgram = false;
+    Fortran::parser::CharBlock mainProgramPosition{};
     llvm::SmallVector<const Fortran::semantics::Symbol *>
         globalOmpRequiresSymbols;
     createBuilderOutsideOfFuncOpAndDo([&]() {
@@ -538,8 +539,10 @@ class FirConverter : public Fortran::lower::AbstractConverter {
         Fortran::common::visit(
             Fortran::common::visitors{
                 [&](Fortran::lower::pft::FunctionLikeUnit &f) {
-                  if (f.isMainProgram())
+                  if (f.isMainProgram()) {
                     hasMainProgram = true;
+                    mainProgramPosition = f.getStartingSourceLoc();
+                  }
                   declareFunction(f);
                   globalOmpRequiresSymbols.push_back(f.getScope().symbol());
                 },
@@ -617,6 +620,9 @@ class FirConverter : public Fortran::lower::AbstractConverter {
     // Generate the `main` entry point if necessary
     if (hasMainProgram)
       createBuilderOutsideOfFuncOpAndDo([&]() {
+        // Lowering has walked every unit, so the current position is the END
+        // statement of the last one. Reset it to the main program's start.
+        setCurrentPosition(mainProgramPosition);
         fir::runtime::genMain(
             *builder, toLocation(), bridge.getEnvironmentDefaults(),
             (getFoldingContext().languageFeatures().IsEnabled(

diff  --git a/flang/test/Lower/main_location.f90 b/flang/test/Lower/main_location.f90
index 73943f845f1ca..31970b3161e92 100644
--- a/flang/test/Lower/main_location.f90
+++ b/flang/test/Lower/main_location.f90
@@ -5,6 +5,9 @@
 ! Check that the missing optional program-stmt (R1401)
 ! does not result in unknown source location of the corresponding
 ! function.
+!
+! Also check that the generated `main` entry point is attributed to the start
+! of the main program unit rather than to its end-stmt.
 
 !--- test1.f90
 if (.false.) then
@@ -16,6 +19,9 @@
 ! TEST1-NEXT: return loc("{{.*}}test1.f90":3:1)
 ! TEST1-NEXT: } loc("{{.*}}test1.f90":1:1)
 
+! TEST1: func.func @main(%{{.*}}: i32 loc("{{.*}}test1.f90":1:1)
+! TEST1: } loc("{{.*}}test1.f90":1:1)
+
 !--- test2.f90
 !!! keep me here
 if (.true.) then
@@ -26,3 +32,6 @@
 ! TEST2-NEXT: fir.dummy_scope : !fir.dscope loc("{{.*}}test2.f90":2:1)
 ! TEST2-NEXT: return loc("{{.*}}test2.f90":4:1)
 ! TEST2-NEXT: } loc("{{.*}}test2.f90":2:1)
+
+! TEST2: func.func @main(%{{.*}}: i32 loc("{{.*}}test2.f90":2:1)
+! TEST2: } loc("{{.*}}test2.f90":2:1)