[PATCH, i386] Partially revert ix86_cannot_change_mode_class changes

[Uros Bizjak]

Hello!

After PR rtl-optimization/69577 fix went in, it looks that we can
remove various kludges involving SSE and MMX register classes from
ix86_cannot_change_mode_class.

2016-02-04  Uros Bizjak  <ubizjak@gmail.com>

    PR rtl-optimization/69577
    Revert:
    2015-10-29  Richard Henderson  <rth@redhat.com>

    PR target/68124
    PR rtl-opt/67609
    * config/i386/i386.c (ix86_cannot_change_mode_class): Tighten
    sse check to the exact conditions of PR 67609.

Patch was bootstrapped and regression tested on x86_64-linux-gnu {,-m32}.

rth, as the author of the patch the attached patch is reverting, does
the patch look OK to you?

Uros.
-------------- next part --------------
Index: config/i386/i386.c
===================================================================
--- config/i386/i386.c	(revision 233143)
+++ config/i386/i386.c	(working copy)
@@ -43283,25 +43283,12 @@ ix86_cannot_change_mode_class (machine_mode from,
 
   if (MAYBE_SSE_CLASS_P (regclass) || MAYBE_MMX_CLASS_P (regclass))
     {
-      int from_size = GET_MODE_SIZE (from);
-      int to_size = GET_MODE_SIZE (to);
-
       /* Vector registers do not support QI or HImode loads.  If we don't
 	 disallow a change to these modes, reload will assume it's ok to
 	 drop the subreg from (subreg:SI (reg:HI 100) 0).  This affects
 	 the vec_dupv4hi pattern.  */
-      if (from_size < 4)
+      if (GET_MODE_SIZE (from) < 4)
 	return true;
-
-      /* Further, we cannot allow word_mode subregs of full vector modes.
-         Otherwise the middle-end will assume it's ok to store to
-         (subreg:DI (reg:TI 100) 0) in order to modify only the low 64 bits
-         of the 128-bit register.  However, after reload the subreg will
-         be dropped leaving a plain DImode store.  This is indistinguishable
-         from a "normal" DImode move, and so we're justified to use movsd,
-         which modifies the entire 128-bit register.  */
-      if (to_size == UNITS_PER_WORD && from_size > UNITS_PER_WORD)
-	return true;
     }
 
   return false;