[gcc r12-8939] Fix wrong array type conversion with different storage orde

[Eric Botcazou <ebotcazou@gcc.gnu.org>]

https://gcc.gnu.org/g:3a34f1f56ad27ac6e1c4765433c06ebd3492b51b

commit r12-8939-g3a34f1f56ad27ac6e1c4765433c06ebd3492b51b
Author: Eric Botcazou <ebotcazou@adacore.com>
Date:   Tue Nov 22 19:03:49 2022 +0100

    Fix wrong array type conversion with different storage orde
    
    When two arrays of scalars have a different storage order in Ada, the
    front-end makes sure that the conversion is performed component-wise
    so that each component can be reversed.  So it's a little bit counter
    productive that the ldist pass performs the opposite transformation
    and synthesizes a memcpy/memmove in this case.
    
    gcc/
            * tree-loop-distribution.cc (loop_distribution::classify_builtin_ldst):
            Bail out if source and destination do not have the same storage order.
    
    gcc/testsuite/
            * gnat.dg/sso18.adb: New test.

Diff:
---
 gcc/testsuite/gnat.dg/sso18.adb | 21 +++++++++++++++++++++
 gcc/tree-loop-distribution.cc   |  7 ++++++-
 2 files changed, 27 insertions(+), 1 deletion(-)

diff --git a/gcc/testsuite/gnat.dg/sso18.adb b/gcc/testsuite/gnat.dg/sso18.adb
new file mode 100644
index 00000000000..7496e965fd3
--- /dev/null
+++ b/gcc/testsuite/gnat.dg/sso18.adb
@@ -0,0 +1,21 @@
+--  { dg-do run }
+--  { dg-options "-O2" }
+
+with System;
+
+procedure SSO18 is
+
+  type Arr is array (1..32) of Short_Integer;
+  type Rev_Arr is array (1..32) of Short_Integer
+    with Scalar_Storage_Order => System.High_Order_First;
+  C : constant Arr := (others => 16);
+  RA : Rev_Arr;
+  A  : Arr;
+
+begin
+  RA := Rev_Arr(C);
+  A := Arr (RA);
+  if A /= C or else RA(1) /= 16 then
+     raise Program_Error;
+  end if;
+end;
diff --git a/gcc/tree-loop-distribution.cc b/gcc/tree-loop-distribution.cc
index bd8d3847fd9..606eb05e64a 100644
--- a/gcc/tree-loop-distribution.cc
+++ b/gcc/tree-loop-distribution.cc
@@ -1770,10 +1770,15 @@ loop_distribution::classify_builtin_ldst (loop_p loop, struct graph *rdg,
   if (res != 2)
     return;
 
-  /* They much have the same access size.  */
+  /* They must have the same access size.  */
   if (!operand_equal_p (size, src_size, 0))
     return;
 
+  /* They must have the same storage order.  */
+  if (reverse_storage_order_for_component_p (DR_REF (dst_dr))
+      != reverse_storage_order_for_component_p (DR_REF (src_dr)))
+    return;
+
   /* Load and store in loop nest must access memory in the same way, i.e,
      their must have the same steps in each loop of the nest.  */
   if (dst_steps.length () != src_steps.length ())