combine.c (combine_simplify_rtx): If nonzero_bits on op shows all bits zero in mode...

	* combine.c (combine_simplify_rtx) <case SUBREG>: If nonzero_bits
	on op shows all bits zero in mode of a lowpart subreg, return zero.

From-SVN: r198595

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index e91ea0027bbbc95e5bec374744a2f521cf03a888..0a56d776b5f9a17419c70c0ed384bb8fcd6a28e2 100644 (file)
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,8 @@
+2013-05-04  Jakub Jelinek  <jakub@redhat.com>
+
+       * combine.c (combine_simplify_rtx) <case SUBREG>: If nonzero_bits
+       on op shows all bits zero in mode of a lowpart subreg, return zero.
+
 2013-05-03  Michael Meissner  <meissner@linux.vnet.ibm.com>
 
        PR target/57150

diff --git a/gcc/combine.c b/gcc/combine.c
index 0792ba3b6f4182a8613698b09e3b62a62310fdf8..b737bc5529fc9d5607aae6ae7288968d8d1ba2bf 100644 (file)
--- a/gcc/combine.c
+++ b/gcc/combine.c
@@ -5417,6 +5417,17 @@ combine_simplify_rtx (rtx x, enum machine_mode op0_mode, int in_dest,
                                SUBREG_BYTE (x));
        if (temp)
          return temp;
+
+       /* If op is known to have all lower bits zero, the result is zero.  */
+       if (!in_dest
+           && SCALAR_INT_MODE_P (mode)
+           && SCALAR_INT_MODE_P (op0_mode)
+           && GET_MODE_PRECISION (mode) < GET_MODE_PRECISION (op0_mode)
+           && subreg_lowpart_offset (mode, op0_mode) == SUBREG_BYTE (x)
+           && HWI_COMPUTABLE_MODE_P (op0_mode)
+           && (nonzero_bits (SUBREG_REG (x), op0_mode)
+               & GET_MODE_MASK (mode)) == 0)
+         return CONST0_RTX (mode);
       }
 
       /* Don't change the mode of the MEM if that would change the meaning