expr.c (expand_expr_real_1): Do not unnecessarily copy the object in the MEM_P case.

* expr.c (expand_expr_real_1) <VIEW_CONVERT_EXPR>: Do not unnecessarily
	copy the object in the MEM_P case.

From-SVN: r192452

gcc/ChangeLog

@@ -1,3 +1,8 @@
+2012-10-15  Eric Botcazou  <ebotcazou@adacore.com>
+
+	* expr.c (expand_expr_real_1) <VIEW_CONVERT_EXPR>: Do not unnecessarily
+	copy the object in the MEM_P case.
+
 2012-10-15  Richard Guenther  <rguenther@suse.de>
 
 	* tree-streamer-out.c (streamer_pack_tree_bitfields): Back
@@ -37,7 +42,6 @@
 	(build_insn_chain): Use df_get_live_out instead of DF_LR_OUT.
 	(do_reload): Remove the DF_LIVE problem for -O1.
 
-
 2012-10-14  Steven Bosscher  <steven@gcc.gnu.org>
 
 	PR rtl-optimization/54919

gcc/expr.c

@@ -10270,10 +10270,15 @@ expand_expr_real_1 (tree exp, rtx target, enum machine_mode tmode,
 	{
 	  enum insn_code icode;
 
-	  op0 = copy_rtx (op0);
-
 	  if (TYPE_ALIGN_OK (type))
-	    set_mem_align (op0, MAX (MEM_ALIGN (op0), TYPE_ALIGN (type)));
+	    {
+	      /* ??? Copying the MEM without substantially changing it might
+		 run afoul of the code handling volatile memory references in
+		 store_expr, which assumes that TARGET is returned unmodified
+		 if it has been used.  */
+	      op0 = copy_rtx (op0);
+	      set_mem_align (op0, MAX (MEM_ALIGN (op0), TYPE_ALIGN (type)));
+	    }
 	  else if (mode != BLKmode
 		   && MEM_ALIGN (op0) < GET_MODE_ALIGNMENT (mode)
 		   /* If the target does have special handling for unaligned

gcc/testsuite/ChangeLog

@@ -1,3 +1,7 @@
+2012-10-15  Eric Botcazou  <ebotcazou@adacore.com>
+
+	* gnat.dg/unchecked_convert9.ad[sb]: New test.
+
 2012-10-13  Jason Merrill  <jason@redhat.com>
 
 	* g++.dg/tls/thread_local7g.C: Require tls_native.

gcc/testsuite/gnat.dg/unchecked_convert9.adb

@@ -0,0 +1,15 @@
+-- { dg-do compile }
+-- { dg-options "-O -fdump-rtl-final" }
+
+package body Unchecked_Convert9 is
+
+   procedure Proc is
+     L : Unsigned_32 := 16#55557777#;
+   begin
+     Var := Conv (L);
+   end;
+
+end Unchecked_Convert9;
+
+-- { dg-final { scan-rtl-dump-times "set \\(mem/v" 1 "final" } }
+-- { dg-final { cleanup-rtl-dump "final" } }

gcc/testsuite/gnat.dg/unchecked_convert9.ads

@@ -0,0 +1,20 @@
+with System;
+with Ada.Unchecked_Conversion;
+with Interfaces; use Interfaces;
+
+package Unchecked_Convert9 is
+
+   type R is record
+     H : Unsigned_16;
+     L : Unsigned_16;
+   end record;
+
+   Var : R;
+   pragma Volatile (Var);
+
+   function Conv is new
+     Ada.Unchecked_Conversion (Source => Unsigned_32, Target => R);
+
+   procedure Proc;
+
+end Unchecked_Convert9;