diff --git a/gcc/lower-subreg.cc b/gcc/lower-subreg.cc
index 481e1e85a26f2e9093e66634689506d3890b4671..81fc5380cbe5ea844010dae1018f9c209c7ff2f6 100644 (file)
--- a/gcc/lower-subreg.cc
+++ b/gcc/lower-subreg.cc
@@ -37,6 +37,7 @@ along with GCC; see the file COPYING3.  If not see
 #include "cfgbuild.h"
 #include "dce.h"
 #include "expr.h"
+#include "explow.h"
 #include "tree-pass.h"
 #include "lower-subreg.h"
 #include "rtl-iter.h"
@@ -1299,11 +1300,12 @@ find_decomposable_shift_zext (rtx_insn *insn, bool speed_p)
 
 /* Decompose a more than word wide shift (in INSN) of a multiword
    pseudo or a multiword zero-extend of a wordmode pseudo into a move
-   and 'set to zero' insn.  Return a pointer to the new insn when a
-   replacement was done.  */
+   and 'set to zero' insn.  SPEED_P says whether we are optimizing
+   for speed or size, when checking if a ZERO_EXTEND is preferable.
+   Return a pointer to the new insn when a replacement was done.  */
 
 static rtx_insn *
-resolve_shift_zext (rtx_insn *insn)
+resolve_shift_zext (rtx_insn *insn, bool speed_p)
 {
   rtx set;
   rtx op;
@@ -1378,14 +1380,29 @@ resolve_shift_zext (rtx_insn *insn)
                                dest_reg, GET_CODE (op) != ASHIFTRT);
     }
 
-  if (dest_reg != src_reg)
-    emit_move_insn (dest_reg, src_reg);
-  if (GET_CODE (op) != ASHIFTRT)
-    emit_move_insn (dest_upper, CONST0_RTX (word_mode));
-  else if (INTVAL (XEXP (op, 1)) == 2 * BITS_PER_WORD - 1)
-    emit_move_insn (dest_upper, copy_rtx (src_reg));
+  /* Consider using ZERO_EXTEND instead of setting DEST_UPPER to zero
+     if this is considered reasonable.  */
+  if (GET_CODE (op) == LSHIFTRT
+      && GET_MODE (op) == twice_word_mode
+      && REG_P (SET_DEST (set))
+      && !choices[speed_p].splitting_zext)
+    {
+      rtx tmp = force_reg (word_mode, copy_rtx (src_reg));
+      tmp = simplify_gen_unary (ZERO_EXTEND, twice_word_mode, tmp, word_mode);
+      emit_move_insn (SET_DEST (set), tmp);
+    }
   else
-    emit_move_insn (dest_upper, upper_src);
+    {
+      if (dest_reg != src_reg)
+       emit_move_insn (dest_reg, src_reg);
+      if (GET_CODE (op) != ASHIFTRT)
+       emit_move_insn (dest_upper, CONST0_RTX (word_mode));
+      else if (INTVAL (XEXP (op, 1)) == 2 * BITS_PER_WORD - 1)
+       emit_move_insn (dest_upper, copy_rtx (src_reg));
+      else
+       emit_move_insn (dest_upper, upper_src);
+    }
+
   insns = get_insns ();
 
   end_sequence ();
@@ -1670,7 +1687,7 @@ decompose_multiword_subregs (bool decompose_copies)
                    {
                      rtx_insn *decomposed_shift;
 
-                     decomposed_shift = resolve_shift_zext (insn);
+                     decomposed_shift = resolve_shift_zext (insn, speed_p);
                      if (decomposed_shift != NULL_RTX)
                        {
                          insn = decomposed_shift;