[flang-commits] [flang] [flang][semantics] fix IsConstantExpr for intrinsic with optional argument (PR #161915)

[Andre Kuhlenschmidt via flang-commits]

https://github.com/akuhlens created https://github.com/llvm/llvm-project/pull/161915

fixes https://github.com/llvm/llvm-project/issues/161694

Exposes that some sequences of duplicate messages are being printed.

>From 5a52dcaad487535733bac61c362d74a9498c3ae4 Mon Sep 17 00:00:00 2001
From: Andre Kuhlenschmidt <akuhlenschmi at nvidia.com>
Date: Fri, 3 Oct 2025 09:32:18 -0700
Subject: [PATCH] initial commit

---
 flang/lib/Evaluate/check-expression.cpp | 17 +++++++++++------
 flang/test/Semantics/intrinsics03.f90   |  5 ++++-
 flang/test/Semantics/intrinsics04.f90   |  5 ++++-
 3 files changed, 19 insertions(+), 8 deletions(-)

diff --git a/flang/lib/Evaluate/check-expression.cpp b/flang/lib/Evaluate/check-expression.cpp
index 8931cbe485ac2..012b44e7d3747 100644
--- a/flang/lib/Evaluate/check-expression.cpp
+++ b/flang/lib/Evaluate/check-expression.cpp
@@ -135,16 +135,21 @@ bool IsConstantExprHelper<INVARIANT>::operator()(
     } else if (proc.IsPure()) {
       std::size_t j{0};
       for (const auto &arg : call.arguments()) {
-        if (const auto *dataDummy{j < proc.dummyArguments.size()
-                    ? std::get_if<characteristics::DummyDataObject>(
-                          &proc.dummyArguments[j].u)
-                    : nullptr};
-            dataDummy &&
+        const auto *dataDummy{j < proc.dummyArguments.size()
+                ? std::get_if<characteristics::DummyDataObject>(
+                      &proc.dummyArguments[j].u)
+                : nullptr};
+        if (dataDummy &&
             dataDummy->attrs.test(
                 characteristics::DummyDataObject::Attr::OnlyIntrinsicInquiry)) {
           // The value of the argument doesn't matter
         } else if (!arg) {
-          return false;
+          // Missing optional arguments are constant
+          if (!(dataDummy &&
+                  dataDummy->attrs.test(
+                      characteristics::DummyDataObject::Attr::Optional))) {
+            return false;
+          }
         } else if (const auto *expr{arg->UnwrapExpr()};
             !expr || !(*this)(*expr)) {
           return false;
diff --git a/flang/test/Semantics/intrinsics03.f90 b/flang/test/Semantics/intrinsics03.f90
index a5b13b655cf41..2b07c5ee98eaf 100644
--- a/flang/test/Semantics/intrinsics03.f90
+++ b/flang/test/Semantics/intrinsics03.f90
@@ -129,6 +129,9 @@ subroutine ichar_tests()
   !Without -Wportability, the warning isn't emitted and the parameter is constant.
   integer, parameter :: a2 = ichar('B ')
   !ERROR: Character in intrinsic function ichar must have length one
-  !ERROR: Must be a constant value
+  !ERROR: Value of named constant 'a3' (ichar("")) cannot be computed as a constant value
+  !ERROR: Character in intrinsic function ichar must have length one
+  !ERROR: Value of named constant 'a3' (ichar("")) cannot be computed as a constant value
+  !ERROR: Character in intrinsic function ichar must have length one
   integer, parameter :: a3 = ichar('')
 end subroutine
diff --git a/flang/test/Semantics/intrinsics04.f90 b/flang/test/Semantics/intrinsics04.f90
index abb8fe321a572..8b6b29fed2128 100644
--- a/flang/test/Semantics/intrinsics04.f90
+++ b/flang/test/Semantics/intrinsics04.f90
@@ -29,6 +29,9 @@ subroutine ichar_tests()
   !WARNING: Character in intrinsic function ichar should have length one [-Wportability]
   integer, parameter :: a2 = ichar('B ')
   !ERROR: Character in intrinsic function ichar must have length one
-  !ERROR: Must be a constant value
+  !ERROR: Value of named constant 'a3' (ichar("")) cannot be computed as a constant value
+  !ERROR: Character in intrinsic function ichar must have length one
+  !ERROR: Value of named constant 'a3' (ichar("")) cannot be computed as a constant value
+  !ERROR: Character in intrinsic function ichar must have length one
   integer, parameter :: a3 = ichar('')
 end subroutine