Fix wrong SRA with VIEW_CONVERT_EXPR and reverse SSO

Most cases of VIEW_CONVERT_EXPRs involving reverse scalar storage order are
disqualified for SRA because they are storage_order_barrier_p, but you can
still have a VIEW_CONVERT_EXPR to a regular composite type being applied to
a component of a record type with reverse scalar storage order.

In this case the bypass for !useless_type_conversion_p in sra_modify_assign,
albeit already heavily guarded, triggers and may generate wrong code, so the
patch makes sure that it does only when the SSO is the same on both side.

gcc/
	* tree-sra.cc (sra_modify_assign): Check that scalar storage order
	is the same on the LHS and RHS before rewriting one with the model
	of the other.
gcc/testsuite/
	* gnat.dg/sso17.adb: New test.

1 files changed, 34 insertions, 0 deletions

diff --git a/gcc/testsuite/gnat.dg/sso17.adb b/gcc/testsuite/gnat.dg/sso17.adb
new file mode 100644
index 0000000..ed57580
--- /dev/null
+++ b/gcc/testsuite/gnat.dg/sso17.adb
@@ -0,0 +1,34 @@
+--  { dg-do run }
+--  { dg-options "-gnatws -O" }
+
+with System;
+
+procedure SSO17 is
+
+  type My_Float is new Float range 0.0 .. 359.99;
+
+  type Rec is record
+    Az : My_Float;
+    El : My_Float;
+  end record;
+  for Rec'Bit_Order use System.High_Order_First;
+  for Rec'Scalar_Storage_Order use System.High_Order_First;
+
+  R : Rec;
+
+  procedure Is_True (B : Boolean);
+  pragma No_Inline (Is_True);
+
+  procedure Is_True (B : Boolean) is
+  begin
+    if not B then
+      raise Program_Error;
+    end if;
+  end;
+
+begin
+  R := (Az => 1.1, El => 2.2);
+  Is_True (R.Az'Valid);
+  R := (Az => 3.3, El => 4.4);
+  Is_True (R.Az'Valid);
+end;