gcc/

	PR middle-end/55438
	* expmed.c (simple_mem_bitfield_p): New function, extracted from
	store_bit_field_1 and extract_bit_field_1.  Use GET_MODE_ALIGNMENT
	rather than bitsize when checking the alignment.
	(store_bit_field_1, extract_bit_field_1): Call it.
	* stor-layout.c (bit_field_mode_iterator::bit_field_mode_iterator):
	Don't limit ALIGN_.  Assume that memory is mapped in chunks of at
	least word size, regardless of BIGGEST_ALIGNMENT.
	(bit_field_mode_iterator::get_mode): Use GET_MODE_ALIGNMENT rather
	than unit when checking the alignment.
	(get_best_mode): Use GET_MODE_ALIGNMENT.


git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@193905 138bc75d-0d04-0410-961f-82ee72b054a4

3 files changed, 43 insertions, 20 deletions

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 5dfe94af589..5350355484c 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,17 @@
+2012-11-28  Richard Sandiford  <rdsandiford@googlemail.com>
+
+	PR middle-end/55438
+	* expmed.c (simple_mem_bitfield_p): New function, extracted from
+	store_bit_field_1 and extract_bit_field_1.  Use GET_MODE_ALIGNMENT
+	rather than bitsize when checking the alignment.
+	(store_bit_field_1, extract_bit_field_1): Call it.
+	* stor-layout.c (bit_field_mode_iterator::bit_field_mode_iterator):
+	Don't limit ALIGN_.  Assume that memory is mapped in chunks of at
+	least word size, regardless of BIGGEST_ALIGNMENT.
+	(bit_field_mode_iterator::get_mode): Use GET_MODE_ALIGNMENT rather
+	than unit when checking the alignment.
+	(get_best_mode): Use GET_MODE_ALIGNMENT.
+
 2012-11-28  Vladimir Makarov  <vmakarov@redhat.com>
 
 	PR rtl-optimization/55512
diff --git a/gcc/expmed.c b/gcc/expmed.c
index fc29ac41d72..d75f031a8c3 100644
--- a/gcc/expmed.c
+++ b/gcc/expmed.c
@@ -416,6 +416,21 @@ lowpart_bit_field_p (unsigned HOST_WIDE_INT bitnum,
   else
     return bitnum % BITS_PER_WORD == 0;
 }
+
+/* Return true if OP is a memory and if a bitfield of size BITSIZE at
+   bit number BITNUM can be treated as a simple value of mode MODE.  */
+
+static bool
+simple_mem_bitfield_p (rtx op0, unsigned HOST_WIDE_INT bitsize,
+		       unsigned HOST_WIDE_INT bitnum, enum machine_mode mode)
+{
+  return (MEM_P (op0)
+	  && bitnum % BITS_PER_UNIT == 0
+	  && bitsize == GET_MODE_BITSIZE (mode)
+	  && (!SLOW_UNALIGNED_ACCESS (mode, MEM_ALIGN (op0))
+	      || (bitnum % GET_MODE_ALIGNMENT (mode) == 0
+		  && MEM_ALIGN (op0) >= GET_MODE_ALIGNMENT (mode))));
+}
 
 /* Try to use instruction INSV to store VALUE into a field of OP0.
    BITSIZE and BITNUM are as for store_bit_field.  */
@@ -624,12 +639,7 @@ store_bit_field_1 (rtx str_rtx, unsigned HOST_WIDE_INT bitsize,
   /* If the target is memory, storing any naturally aligned field can be
      done with a simple store.  For targets that support fast unaligned
      memory, any naturally sized, unit aligned field can be done directly.  */
-  if (MEM_P (op0)
-      && bitnum % BITS_PER_UNIT == 0
-      && bitsize == GET_MODE_BITSIZE (fieldmode)
-      && (!SLOW_UNALIGNED_ACCESS (fieldmode, MEM_ALIGN (op0))
-	  || (bitnum % bitsize == 0
-	      && MEM_ALIGN (op0) % bitsize == 0)))
+  if (simple_mem_bitfield_p (op0, bitsize, bitnum, fieldmode))
     {
       op0 = adjust_bitfield_address (op0, fieldmode, bitnum / BITS_PER_UNIT);
       emit_move_insn (op0, value);
@@ -1455,12 +1465,7 @@ extract_bit_field_1 (rtx str_rtx, unsigned HOST_WIDE_INT bitsize,
 
   /* Extraction of a full MODE1 value can be done with a load as long as
      the field is on a byte boundary and is sufficiently aligned.  */
-  if (MEM_P (op0)
-      && bitnum % BITS_PER_UNIT == 0
-      && bitsize == GET_MODE_BITSIZE (mode1)
-      && (!SLOW_UNALIGNED_ACCESS (mode1, MEM_ALIGN (op0))
-	  || (bitnum % bitsize == 0
-	      && MEM_ALIGN (op0) % bitsize == 0)))
+  if (simple_mem_bitfield_p (op0, bitsize, bitnum, mode1))
     {
       op0 = adjust_bitfield_address (op0, mode1, bitnum / BITS_PER_UNIT);
       return convert_extracted_bit_field (op0, mode, tmode, unsignedp);
diff --git a/gcc/stor-layout.c b/gcc/stor-layout.c
index d0c093f9364..3d97796da5c 100644
--- a/gcc/stor-layout.c
+++ b/gcc/stor-layout.c
@@ -2643,15 +2643,17 @@ bit_field_mode_iterator
 			   unsigned int align, bool volatilep)
 : mode_ (GET_CLASS_NARROWEST_MODE (MODE_INT)), bitsize_ (bitsize),
   bitpos_ (bitpos), bitregion_start_ (bitregion_start),
-  bitregion_end_ (bitregion_end), align_ (MIN (align, BIGGEST_ALIGNMENT)),
+  bitregion_end_ (bitregion_end), align_ (align),
   volatilep_ (volatilep), count_ (0)
 {
   if (!bitregion_end_)
     {
-      /* We can assume that any aligned chunk of ALIGN_ bits that overlaps
+      /* We can assume that any aligned chunk of UNITS bits that overlaps
 	 the bitfield is mapped and won't trap.  */
-      bitregion_end_ = bitpos + bitsize + align_ - 1;
-      bitregion_end_ -= bitregion_end_ % align_ + 1;
+      unsigned HOST_WIDE_INT units = MIN (align, MAX (BIGGEST_ALIGNMENT,
+						      BITS_PER_WORD));
+      bitregion_end_ = bitpos + bitsize + units - 1;
+      bitregion_end_ -= bitregion_end_ % units + 1;
     }
 }
 
@@ -2694,7 +2696,8 @@ bit_field_mode_iterator::next_mode (enum machine_mode *out_mode)
 	break;
 
       /* Stop if the mode requires too much alignment.  */
-      if (unit > align_ && SLOW_UNALIGNED_ACCESS (mode_, align_))
+      if (GET_MODE_ALIGNMENT (mode_) > align_
+	  && SLOW_UNALIGNED_ACCESS (mode_, align_))
 	break;
 
       *out_mode = mode_;
@@ -2753,8 +2756,9 @@ get_best_mode (int bitsize, int bitpos,
   enum machine_mode widest_mode = VOIDmode;
   enum machine_mode mode;
   while (iter.next_mode (&mode)
-	 /* ??? For historical reasons, reject modes that are wider than
-	    the alignment.  This has both advantages and disadvantages.
+	 /* ??? For historical reasons, reject modes that would normally
+	    receive greater alignment, even if unaligned accesses are
+	    acceptable.  This has both advantages and disadvantages.
 	    Removing this check means that something like:
 
 	       struct s { unsigned int x; unsigned int y; };
@@ -2808,7 +2812,7 @@ get_best_mode (int bitsize, int bitpos,
 	    causes store_bit_field to keep a 128-bit memory reference,
 	    so that the final bitfield reference still has a MEM_EXPR
 	    and MEM_OFFSET.  */
-	 && GET_MODE_BITSIZE (mode) <= align
+	 && GET_MODE_ALIGNMENT (mode) <= align
 	 && (largest_mode == VOIDmode
 	     || GET_MODE_SIZE (mode) <= GET_MODE_SIZE (largest_mode)))
     {