[flang-commits] [flang] [flang][Semantics] Ensure deterministic mod file output (PR #128655)

[Iñaki Amatria Barral via flang-commits]

https://github.com/inaki-amatria updated https://github.com/llvm/llvm-project/pull/128655

>From ff35d6e73f5f637d09bcf3ad9afed1399f8f6cf4 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?I=C3=B1aki=20Amatria=20Barral?= <inaki.amatria at appentra.com>
Date: Tue, 25 Feb 2025 09:18:45 +0100
Subject: [PATCH] [flang] Ensure deterministic mod file output

---
 flang/lib/Semantics/mod-file.cpp          | 21 ++---------------
 flang/test/Semantics/Inputs/modfile72.f90 | 13 +++++++++++
 flang/test/Semantics/modfile72.f90        | 28 +++++++++++++++++++++++
 3 files changed, 43 insertions(+), 19 deletions(-)
 create mode 100644 flang/test/Semantics/Inputs/modfile72.f90
 create mode 100644 flang/test/Semantics/modfile72.f90

diff --git a/flang/lib/Semantics/mod-file.cpp b/flang/lib/Semantics/mod-file.cpp
index bef934beaacfa..82c43d96bea44 100644
--- a/flang/lib/Semantics/mod-file.cpp
+++ b/flang/lib/Semantics/mod-file.cpp
@@ -836,18 +836,6 @@ void ModFileWriter::PutUseExtraAttr(
   }
 }
 
-static inline SourceName NameInModuleFile(const Symbol &symbol) {
-  if (const auto *use{symbol.detailsIf<UseDetails>()}) {
-    if (use->symbol().attrs().test(Attr::PRIVATE)) {
-      // Avoid the use in sorting of names created to access private
-      // specific procedures as a result of generic resolution;
-      // they're not in the cooked source.
-      return use->symbol().name();
-    }
-  }
-  return symbol.name();
-}
-
 // Collect the symbols of this scope sorted by their original order, not name.
 // Generics and namelists are exceptions: they are sorted after other symbols.
 void CollectSymbols(const Scope &scope, SymbolVector &sorted,
@@ -882,13 +870,8 @@ void CollectSymbols(const Scope &scope, SymbolVector &sorted,
       sorted.push_back(symbol);
     }
   }
-  // Sort most symbols by name: use of Symbol::ReplaceName ensures the source
-  // location of a symbol's name is the first "real" use.
-  auto sorter{[](SymbolRef x, SymbolRef y) {
-    return NameInModuleFile(*x).begin() < NameInModuleFile(*y).begin();
-  }};
-  std::sort(sorted.begin(), sorted.end(), sorter);
-  std::sort(generics.begin(), generics.end(), sorter);
+  std::sort(sorted.begin(), sorted.end(), SymbolSourcePositionCompare{});
+  std::sort(generics.begin(), generics.end(), SymbolSourcePositionCompare{});
   sorted.insert(sorted.end(), generics.begin(), generics.end());
   sorted.insert(sorted.end(), namelist.begin(), namelist.end());
   for (const auto &pair : scope.commonBlocks()) {
diff --git a/flang/test/Semantics/Inputs/modfile72.f90 b/flang/test/Semantics/Inputs/modfile72.f90
new file mode 100644
index 0000000000000..2601821cd6a0b
--- /dev/null
+++ b/flang/test/Semantics/Inputs/modfile72.f90
@@ -0,0 +1,13 @@
+module foo
+  interface do_foo
+    procedure do_foo_impl
+  end interface
+  interface do_bar
+    procedure do_bar_impl
+  end interface
+contains
+  subroutine do_foo_impl()
+  end
+  subroutine do_bar_impl()
+  end
+end
diff --git a/flang/test/Semantics/modfile72.f90 b/flang/test/Semantics/modfile72.f90
new file mode 100644
index 0000000000000..0668d605eaa09
--- /dev/null
+++ b/flang/test/Semantics/modfile72.f90
@@ -0,0 +1,28 @@
+! This test verifies that both invocations produce a consistent order in the
+! generated `.mod` file. Previous versions of Flang exhibited non-deterministic
+! behavior due to pointers outside the cooked source being used to order symbols
+! in the `.mod` file.
+
+! RUN: rm -rf %t && mkdir -p %t
+! RUN: %flang_fc1 -fsyntax-only -J%t %S/Inputs/modfile72.f90
+! RUN: %flang_fc1 -fsyntax-only -J%t %s
+! RUN: cat %t/bar.mod | FileCheck %s
+
+! RUN: rm -rf %t && mkdir -p %t
+! RUN: %flang_fc1 -fsyntax-only -J%t %S/Inputs/modfile72.f90 %s
+! RUN: cat %t/bar.mod | FileCheck %s
+
+module bar
+  use foo, only : do_foo
+  use foo, only : do_bar
+contains
+  subroutine do_baz()
+    call do_foo()
+    call do_bar()
+  end
+end
+
+!      CHECK: use foo,only:do_foo
+! CHECK-NEXT: use foo,only:do_bar
+! CHECK-NEXT: use foo,only:foo$foo$do_bar_impl=>do_bar_impl
+! CHECK-NEXT: use foo,only:foo$foo$do_foo_impl=>do_foo_impl