[flang-commits] [flang] [flang] Translate +x to (x), not x (PR #157513)

[Peter Klausler via flang-commits]

https://github.com/klausler created https://github.com/llvm/llvm-project/pull/157513

In expression semantics, don't completely delete the unary plus operator, but instead translate it into parentheses.  The distinction matters in contexts where the bounds of x are significant or when x must not be misinterpreted as a variable.

Fixes https://github.com/llvm/llvm-project/issues/157379.

>From 1fa55cdcdc7a11634f0499364681eb7824cbe2c9 Mon Sep 17 00:00:00 2001
From: Peter Klausler <pklausler at nvidia.com>
Date: Mon, 8 Sep 2025 10:05:30 -0700
Subject: [PATCH] [flang] Translate +x to (x), not x

In expression semantics, don't completely delete the unary plus
operator, but instead translate it into parentheses.  The distinction
matters in contexts where the bounds of x are significant or when
x must not be misinterpreted as a variable.

Fixes https://github.com/llvm/llvm-project/issues/157379.
---
 flang/lib/Semantics/expression.cpp |  5 ++++-
 flang/test/Evaluate/bug157379.f90  | 13 +++++++++++++
 2 files changed, 17 insertions(+), 1 deletion(-)
 create mode 100644 flang/test/Evaluate/bug157379.f90

diff --git a/flang/lib/Semantics/expression.cpp b/flang/lib/Semantics/expression.cpp
index ccccf60adae5d..3f048ab6f7a4d 100644
--- a/flang/lib/Semantics/expression.cpp
+++ b/flang/lib/Semantics/expression.cpp
@@ -3700,7 +3700,10 @@ static MaybeExpr NumericUnaryHelper(ExpressionAnalyzer &context,
       analyzer.CheckForNullPointer();
       analyzer.CheckForAssumedRank();
       if (opr == NumericOperator::Add) {
-        return analyzer.MoveExpr(0);
+        // +x -> (x), not a bare x, because the bounds of the argument must
+        // not be exposed to allocatable assignments or structure constructor
+        // components.
+        return Parenthesize(analyzer.MoveExpr(0));
       } else {
         return Negation(context.GetContextualMessages(), analyzer.MoveExpr(0));
       }
diff --git a/flang/test/Evaluate/bug157379.f90 b/flang/test/Evaluate/bug157379.f90
new file mode 100644
index 0000000000000..53aac4c29d3e4
--- /dev/null
+++ b/flang/test/Evaluate/bug157379.f90
@@ -0,0 +1,13 @@
+! RUN: %flang_fc1 -fdebug-unparse %s 2>&1 | FileCheck %s
+program main
+  type t
+    integer, allocatable :: ia(:)
+  end type
+  type(t) x
+  integer, allocatable :: ja(:)
+  allocate(ja(2:2))
+  ja(2) = 2
+  !CHECK: x=t(ia=(ja))
+  x = t(+ja)            ! must be t(ia=(ja)), not t(ia=ja)
+  print *, lbound(x%ia) ! must be 1, not 2
+end