From: Mikael Morin <mik...@gcc.gnu.org>

Changes v1 -> v2:
 - Also handle complex conjugate operator.
 - Don't create the NON_LVALUE_EXPR if there is a type conversion between the
   doubled operators.

Regression tested on x86_64-linux.  OK for master?

-- 8< --

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.
---
 gcc/match.pd                               | 10 +++++--
 gcc/testsuite/gfortran.dg/non_lvalue_1.f90 | 32 ++++++++++++++++++++++
 2 files changed, 39 insertions(+), 3 deletions(-)
 create mode 100644 gcc/testsuite/gfortran.dg/non_lvalue_1.f90

diff --git a/gcc/match.pd b/gcc/match.pd
index 0f53c162fce..372d4657baa 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 +4037,9 @@ 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)))
+   (if (GENERIC && type == TREE_TYPE (@1))
+    (non_lvalue @1)
+    (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 +5769,9 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
 (simplify
  (conj (convert? (conj @0)))
  (if (tree_nop_conversion_p (TREE_TYPE (@0), type))
-  (convert @0)))
+  (if (GENERIC && type == TREE_TYPE (@0))
+   (non_lvalue @0)
+   (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 00000000000..61dad5a2ce1
--- /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" } }
-- 
2.47.2

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