[gcc(refs/users/mikael/heads/non_lvalue_v05)] match: Simplify doubled not, negate and conjugate operators to a non_lvalue

[Mikael Morin]

https://gcc.gnu.org/g:85b4eb8956df894da3819cbbda4388ff6667fc23

commit 85b4eb8956df894da3819cbbda4388ff6667fc23
Author: Mikael Morin <morin-mikael@orange.fr>
Date:   Sat Jun 21 20:12:31 2025 +0200

    match: Simplify doubled not, negate and conjugate operators to a non_lvalue
    
    gcc/ChangeLog:
    
            * match.pd (`-(-X)`, `~(~X)`, `conj(conj(X))`): Add a
            NON_LVALUE_EXPR wrapper to the simplification of doubled unary
            operators NEGATE_EXPR, BIT_NOT_EXPR and CONJ_EXPR.
    
    gcc/testsuite/ChangeLog:
    
            * gfortran.dg/non_lvalue_1.f90: New test.

Diff:
---
 gcc/match.pd                               |  6 +++---
 gcc/testsuite/gfortran.dg/non_lvalue_1.f90 | 32 ++++++++++++++++++++++++++++++
 2 files changed, 35 insertions(+), 3 deletions(-)

diff --git a/gcc/match.pd b/gcc/match.pd
index 0f53c162fce3..f4416d9172c4 100644
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -2357,7 +2357,7 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
 /* ~~x -> x */
 (simplify
   (bit_not (bit_not @0))
-  @0)
+  (non_lvalue @0))
 
 /* zero_one_valued_p will match when a value is known to be either
    0 or 1 including constants 0 or 1.
@@ -4037,7 +4037,7 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
   (negate (nop_convert? (negate @1)))
   (if (!TYPE_OVERFLOW_SANITIZED (type)
        && !TYPE_OVERFLOW_SANITIZED (TREE_TYPE (@1)))
-   (view_convert @1)))
+   (non_lvalue (view_convert @1))))
 
  /* We can't reassociate floating-point unless -fassociative-math
     or fixed-point plus or minus because of saturation to +-Inf.  */
@@ -5767,7 +5767,7 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
 (simplify
  (conj (convert? (conj @0)))
  (if (tree_nop_conversion_p (TREE_TYPE (@0), type))
-  (convert @0)))
+  (non_lvalue (convert @0))))
 
 /* conj({x,y}) -> {x,-y}  */
 (simplify
diff --git a/gcc/testsuite/gfortran.dg/non_lvalue_1.f90 b/gcc/testsuite/gfortran.dg/non_lvalue_1.f90
new file mode 100644
index 000000000000..61dad5a2ce1b
--- /dev/null
+++ b/gcc/testsuite/gfortran.dg/non_lvalue_1.f90
@@ -0,0 +1,32 @@
+! { dg-do compile }
+! { dg-additional-options "-fdump-tree-original" }
+!
+! Check the generation of NON_LVALUE_EXPR expressions in cases where a unary
+! operator expression would simplify to a bare data reference.
+
+! A NON_LVALUE_EXPR is generated for a double negation that would simplify to
+! a bare data reference.
+function f1 (f1_arg1)
+  integer, value :: f1_arg1
+  integer :: f1
+  f1 = -(-f1_arg1)
+end function
+! { dg-final { scan-tree-dump "__result_f1 = NON_LVALUE_EXPR <f1_arg1>;" "original" } }
+
+! A NON_LVALUE_EXPR is generated for a double complement that would simplify to
+! a bare data reference.
+function f2 (f2_arg1)
+  integer, value :: f2_arg1
+  integer :: f2
+  f2 = not(not(f2_arg1))
+end function
+! { dg-final { scan-tree-dump "__result_f2 = NON_LVALUE_EXPR <f2_arg1>;" "original" } }
+
+! A NON_LVALUE_EXPR is generated for a double complex conjugate that would
+! simplify to a bare data reference.
+function f3 (f3_arg1)
+  complex, value :: f3_arg1
+  complex :: f3
+  f3 = conjg(conjg(f3_arg1))
+end function
+! { dg-final { scan-tree-dump "__result_f3 = NON_LVALUE_EXPR <f3_arg1>;" "original" } }