[flang-commits] [flang] [flang] Fix purity checking for internal subprograms (PR #91759)

[Peter Klausler via flang-commits]

https://github.com/klausler created https://github.com/llvm/llvm-project/pull/91759

ELEMENTAL internal subprograms are pure unless explicitly IMPURE.

>From 5ba70a64df399a648fbc4d93f9c4c46afd7eaee8 Mon Sep 17 00:00:00 2001
From: Peter Klausler <pklausler at nvidia.com>
Date: Fri, 10 May 2024 08:41:31 -0700
Subject: [PATCH] [flang] Fix purity checking for internal subprograms

ELEMENTAL internal subprograms are pure unless explicitly IMPURE.
---
 flang/lib/Semantics/check-purity.cpp | 10 +++--
 flang/test/Semantics/pure02.f90      | 59 ++++++++++++++++++++++++++++
 2 files changed, 66 insertions(+), 3 deletions(-)
 create mode 100644 flang/test/Semantics/pure02.f90

diff --git a/flang/lib/Semantics/check-purity.cpp b/flang/lib/Semantics/check-purity.cpp
index 5176390f366bd..55a9a2f107388 100644
--- a/flang/lib/Semantics/check-purity.cpp
+++ b/flang/lib/Semantics/check-purity.cpp
@@ -39,12 +39,16 @@ bool PurityChecker::InPureSubprogram() const {
 
 bool PurityChecker::HasPurePrefix(
     const std::list<parser::PrefixSpec> &prefixes) const {
+  bool result{false};
   for (const parser::PrefixSpec &prefix : prefixes) {
-    if (std::holds_alternative<parser::PrefixSpec::Pure>(prefix.u)) {
-      return true;
+    if (std::holds_alternative<parser::PrefixSpec::Impure>(prefix.u)) {
+      return false;
+    } else if (std::holds_alternative<parser::PrefixSpec::Pure>(prefix.u) ||
+        std::holds_alternative<parser::PrefixSpec::Elemental>(prefix.u)) {
+      result = true;
     }
   }
-  return false;
+  return result;
 }
 
 void PurityChecker::Entered(
diff --git a/flang/test/Semantics/pure02.f90 b/flang/test/Semantics/pure02.f90
new file mode 100644
index 0000000000000..11dc0fd268293
--- /dev/null
+++ b/flang/test/Semantics/pure02.f90
@@ -0,0 +1,59 @@
+! RUN: %python %S/test_errors.py %s %flang_fc1
+pure subroutine s1
+ contains
+  !ERROR: An internal subprogram of a pure subprogram must also be pure
+  subroutine t1
+  end
+  pure subroutine t2 ! ok
+  end
+  elemental subroutine t3(k) ! ok
+    integer, intent(in) :: k
+  end
+  !ERROR: An internal subprogram of a pure subprogram must also be pure
+  impure elemental subroutine t4(k)
+    integer, intent(in) :: k
+  end
+  !ERROR: An internal subprogram of a pure subprogram must also be pure
+  elemental impure subroutine t5(k)
+    integer, intent(in) :: k
+  end
+end
+
+elemental subroutine s2(j)
+  integer, intent(in) :: j
+ contains
+  !ERROR: An internal subprogram of a pure subprogram must also be pure
+  subroutine t1
+  end
+  pure subroutine t2 ! ok
+  end
+  elemental subroutine t3(k) ! ok
+    integer, intent(in) :: k
+  end
+  !ERROR: An internal subprogram of a pure subprogram must also be pure
+  impure elemental subroutine t4(k)
+    integer, intent(in) :: k
+  end
+  !ERROR: An internal subprogram of a pure subprogram must also be pure
+  elemental impure subroutine t5(k)
+    integer, intent(in) :: k
+  end
+end
+
+impure elemental subroutine s3(j)
+  integer, intent(in) :: j
+ contains
+  subroutine t1
+  end
+  pure subroutine t2
+  end
+  elemental subroutine t3(k)
+    integer, intent(in) :: k
+  end
+  impure elemental subroutine t4(k)
+    integer, intent(in) :: k
+  end
+  elemental impure subroutine t5(k)
+    integer, intent(in) :: k
+  end
+end