[Patch] Fortran: Fix non_negative_strides_array_p

[Tobias Burnus <tobias@codesourcery.com>]

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First, I am woefully aware that there several patches pending. I hope to do a
couple of reviews later today or in the next days.

Otherwise, I did run into another issue in existing code which was exposed by
the delinearization patch on the OG12 branch, but could potentially lead to
wrong code on mainline as well, depending on how the return value is used.
Albeit I did fail to create a testcase for it.

OK for mainline?

Tobias
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Fortran: Fix non_negative_strides_array_p

The non_negative_strides_array_p function might return wrongly 'true', e.g.
for assumed-shape arrays, if the argument is '*a.0 ...' instead of 'a.0 ...'
as then the saved array descriptor for the PARAM_DECL 'a' is not found.

This potentially leads to wrong code - but I could not find a testcase
leading to wrong code on mainline. Asserts show that this happens with
CLASS; however, for those no ARRAY_REF seems to get used.

The issue show up when applying the delinearization patch as posted
at https://gcc.gnu.org/pipermail/gcc-patches/2020-December/562230.html
that has been applied to the OG12 alias devel/omp/gcc-12 vendor branch, as
commit 39a8c371fda6136cf77c74895a00b136409e0ba3. This patch calls
gfc_build_array_ref inside gfc_conv_array_ref. The issue mentioned
above show up with this patch in gfortran.dg/array_reference_3.f90,
a testcase added together with non_negative_strides_array_p in commit
r12-8230-g7964ab6c364 for PR 102043. Here, non_negative_strides_array_p
returns true for assumed_shape_x but assumed shape arrays may have
negative strides.

gcc/fortran/ChangeLog:

	* trans-array.cc (non_negative_strides_array_p): Fix handling
	of GFC_DECL_SAVED_DESCRIPTOR.

 gcc/fortran/trans-array.cc | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/gcc/fortran/trans-array.cc b/gcc/fortran/trans-array.cc
index 795ce14af08..ca3503b7cae 100644
--- a/gcc/fortran/trans-array.cc
+++ b/gcc/fortran/trans-array.cc
@@ -3695,11 +3695,16 @@ non_negative_strides_array_p (tree expr)
 
   /* If the array was originally a dummy with a descriptor, strides can be
      negative.  */
-  if (DECL_P (expr)
-      && DECL_LANG_SPECIFIC (expr)
-      && GFC_DECL_SAVED_DESCRIPTOR (expr)
-      && GFC_DECL_SAVED_DESCRIPTOR (expr) != expr)
-    return non_negative_strides_array_p (GFC_DECL_SAVED_DESCRIPTOR (expr));
+  tree decl = expr;
+  STRIP_NOPS (decl);
+  if (TREE_CODE (decl) == INDIRECT_REF)
+    decl = TREE_OPERAND (decl, 0);
+
+  if (DECL_P (decl)
+      && DECL_LANG_SPECIFIC (decl)
+      && GFC_DECL_SAVED_DESCRIPTOR (decl)
+      && GFC_DECL_SAVED_DESCRIPTOR (decl) != expr)
+    return non_negative_strides_array_p (GFC_DECL_SAVED_DESCRIPTOR (decl));
 
   return true;
 }