Fix ICE with scalar_storage_order attribute at -O

[Eric Botcazou <ebotcazou@adacore.com>]

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This is a regression present on the mainline in the form of an assertion 
failure in optimize_bitfield_assignment_op with a scalar_storage_order 
attribute specifying the reverse endianness wrt the native endianness.

I put this assertion because I failed to cover the path at the time but things 
have changed since then and the attached testcase triggers it now (and also 
checks that the generated code is correct in this case).

Tested on x86_64-suse-linux, applied on the mainline.


2018-02-09  Eric Botcazou  <ebotcazou@adacore.com>

	* expr.c (optimize_bitfield_assignment_op): Remove obsolete assertion.


2018-02-09  Eric Botcazou  <ebotcazou@adacore.com>

	* gnat.dg/sso8.adb: New test.
	* gnat.dg/sso8_pkg.ads: New helper.

-- 
Eric Botcazou

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Index: expr.c
===================================================================
--- expr.c	(revision 257404)
+++ expr.c	(working copy)
@@ -4726,8 +4726,6 @@ optimize_bitfield_assignment_op (poly_ui
     }
   else if (!REG_P (str_rtx) && GET_CODE (str_rtx) != SUBREG)
     return false;
-  else
-    gcc_assert (!reverse);
 
   /* If the bit field covers the whole REG/MEM, store_field
      will likely generate better code.  */

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with Interfaces;
with System;
with Unchecked_Conversion;

package SSO8_Pkg is

  Val8 : Interfaces.Unsigned_8;

  type Two_Bit_Int is range 0 .. 3;
  for Two_Bit_Int'size use 2;

  type Arr is array (1 .. 5) of Boolean;
  for Arr'scalar_storage_order use System.High_Order_First;
  pragma Pack (Arr);

  type Rec is record
    Boolean_Data : Boolean;
    Array_Data   : Arr;
    Two_Bit_Data : Two_Bit_Int;
  end record;
  for Rec use record
    Boolean_Data at 0 range 0 .. 0;
    Array_Data   at 0 range 1 .. 5;
    Two_Bit_Data at 0 range 6 .. 7;
  end record;
  for Rec'size use 8;
  for Rec'bit_order use System.High_Order_First;
  for Rec'scalar_storage_order use System.High_Order_First;

  function Conv is new Unchecked_Conversion (Rec, Interfaces.Unsigned_8);

end SSO8_Pkg;

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-- { dg-do run }
-- { dg-options "-O" }

with Interfaces; use Interfaces;
with SSO8_Pkg; use SSO8_Pkg;

procedure SSO8 is
  Data : Rec;
begin
  Data.Array_Data (2) := True;
  Val8 := Conv (Data);
  if Val8 /= 32 then
    raise Program_Error;
  end if;
end;