re PR rtl-optimization/33927 (replace_read in dse.c could handle cases where GET_MODE_CLASS (read_mode) != GET_MODE_CLASS (store_mode) (and the size is the same))

gcc/
	PR rtl-optimization/33927
	* Makefile.in (dse.o): Depend on $(TM_P_H).
	* expr.h (extract_low_bits): Declare.
	* expmed.c (extract_low_bits): New function.
	* rtlhooks.c (gen_lowpart_general): Generalize SUBREG handling.
	* dse.c: Include tm_p.h.
	(find_shift_sequence): Remove the read_reg argument and return the
	read value.  Emit the instructions instead of returning them.
	Iterate on new_mode rather than calculating it each time.
	Check MODES_TIEABLE_P.  Use simplify_gen_subreg to convert the
	source to NEW_MODE and extract_low_bits to convert the shifted
	value to READ_MODE.
	(replace_read): Allow the load and store to have different mode
	classes.  Use extract_low_bits when SHIFT == 0.  Create the shift
	or extraction instructions before trying the replacement.  Update
	dump-file code accordingly, avoiding use of REGNO (store_info->rhs).

gcc/testsuite/
	* gcc.target/mips/dse-1.c: Add checks for zeros.

From-SVN: r133452

1 files changed, 66 insertions, 87 deletions

diff --git a/gcc/dse.c b/gcc/dse.c
index fea7afa..696b2d8 100644
--- a/gcc/dse.c
+++ b/gcc/dse.c
@@ -29,6 +29,7 @@ along with GCC; see the file COPYING3.  If not see
 #include "tm.h"
 #include "rtl.h"
 #include "tree.h"
+#include "tm_p.h"
 #include "regs.h"
 #include "hard-reg-set.h"
 #include "flags.h"
@@ -1383,9 +1384,9 @@ record_store (rtx body, bb_info_t bb_info)
   if (store_info->is_set 
       /* No place to keep the value after ra.  */
       && !reload_completed
-      /* The careful reviewer may wish to comment my checking that the
-	 rhs of a store is always a reg.  */
-      && REG_P (SET_SRC (body))
+      && (REG_P (SET_SRC (body))
+	  || GET_CODE (SET_SRC (body)) == SUBREG
+	  || CONSTANT_P (SET_SRC (body)))
       /* Sometimes the store and reload is used for truncation and
 	 rounding.  */
       && !(FLOAT_MODE_P (GET_MODE (mem)) && (flag_float_store)))
@@ -1418,15 +1419,15 @@ dump_insn_info (const char * start, insn_info_t insn_info)
    shift.  */
 
 static rtx
-find_shift_sequence (rtx read_reg,
-		     int access_size,
+find_shift_sequence (int access_size,
 		     store_info_t store_info,
 		     read_info_t read_info,
 		     int shift)
 {
   enum machine_mode store_mode = GET_MODE (store_info->mem);
   enum machine_mode read_mode = GET_MODE (read_info->mem);
-  rtx chosen_seq = NULL;
+  enum machine_mode new_mode;
+  rtx read_reg = NULL;
 
   /* Some machines like the x86 have shift insns for each size of
      operand.  Other machines like the ppc or the ia-64 may only have
@@ -1435,21 +1436,31 @@ find_shift_sequence (rtx read_reg,
      justify the value we want to read but is available in one insn on
      the machine.  */
 
-  for (; access_size <= UNITS_PER_WORD; access_size *= 2)
+  for (new_mode = smallest_mode_for_size (access_size * BITS_PER_UNIT,
+					  MODE_INT);
+       GET_MODE_BITSIZE (new_mode) <= BITS_PER_WORD;
+       new_mode = GET_MODE_WIDER_MODE (new_mode))
     {
-      rtx target, new_reg, shift_seq, insn;
-      enum machine_mode new_mode;
+      rtx target, new_reg, shift_seq, insn, new_lhs;
       int cost;
 
-      /* Try a wider mode if truncating the store mode to ACCESS_SIZE
-	 bytes requires a real instruction.  */
-      if (access_size < GET_MODE_SIZE (store_mode)
-	  && !TRULY_NOOP_TRUNCATION (access_size * BITS_PER_UNIT,
+      /* Try a wider mode if truncating the store mode to NEW_MODE
+	 requires a real instruction.  */
+      if (GET_MODE_BITSIZE (new_mode) < GET_MODE_BITSIZE (store_mode)
+	  && !TRULY_NOOP_TRUNCATION (GET_MODE_BITSIZE (new_mode),
 				     GET_MODE_BITSIZE (store_mode)))
 	continue;
 
-      new_mode = smallest_mode_for_size (access_size * BITS_PER_UNIT,
-					 MODE_INT);
+      /* Also try a wider mode if the necessary punning is either not
+	 desirable or not possible.  */
+      if (!CONSTANT_P (store_info->rhs)
+	  && !MODES_TIEABLE_P (new_mode, store_mode))
+	continue;
+      new_lhs = simplify_gen_subreg (new_mode, copy_rtx (store_info->rhs),
+				     store_mode, 0);
+      if (new_lhs == NULL_RTX)
+	continue;
+
       new_reg = gen_reg_rtx (new_mode);
 
       start_sequence ();
@@ -1485,31 +1496,13 @@ find_shift_sequence (rtx read_reg,
 	 take the value from the store and put it into the
 	 shift pseudo, then shift it, then generate another
 	 move to put in into the target of the read.  */
-      start_sequence ();
-      emit_move_insn (new_reg, gen_lowpart (new_mode, store_info->rhs));
+      emit_move_insn (new_reg, new_lhs);
       emit_insn (shift_seq);
-      convert_move (read_reg, new_reg, 1);
-		  
-      if (dump_file)
-	{
-	  fprintf (dump_file, " -- adding extract insn r%d:%s = r%d:%s\n",
-		   REGNO (new_reg), GET_MODE_NAME (new_mode),
-		   REGNO (store_info->rhs), GET_MODE_NAME (store_mode));
-		      
-	  fprintf (dump_file, " -- with shift of r%d by %d\n",
-		   REGNO(new_reg), shift);
-	  fprintf (dump_file, " -- and second extract insn r%d:%s = r%d:%s\n",
-		   REGNO (read_reg), GET_MODE_NAME (read_mode),
-		   REGNO (new_reg), GET_MODE_NAME (new_mode));
-	}
-		  
-      /* Get the three insn sequence and return it.  */
-      chosen_seq = get_insns ();
-      end_sequence ();
+      read_reg = extract_low_bits (read_mode, new_mode, new_reg);
       break;
     }
 
-  return chosen_seq;
+  return read_reg;
 }
 
 
@@ -1552,16 +1545,11 @@ replace_read (store_info_t store_info, insn_info_t store_insn,
   enum machine_mode read_mode = GET_MODE (read_info->mem);
   int shift;
   int access_size; /* In bytes.  */
-  rtx read_reg = gen_reg_rtx (read_mode);
-  rtx shift_seq = NULL;
+  rtx insns, read_reg;
 
   if (!dbg_cnt (dse))
     return false;
 
-  if (GET_MODE_CLASS (read_mode) != MODE_INT
-      || GET_MODE_CLASS (store_mode) != MODE_INT)
-    return false;
-
   /* To get here the read is within the boundaries of the write so
      shift will never be negative.  Start out with the shift being in
      bytes.  */
@@ -1575,62 +1563,43 @@ replace_read (store_info_t store_info, insn_info_t store_insn,
   /* From now on it is bits.  */
   shift *= BITS_PER_UNIT;
 
-  /* We need to keep this in perspective.  We are replacing a read
+  /* Create a sequence of instructions to set up the read register.
+     This sequence goes immediately before the store and its result
+     is read by the load.
+
+     We need to keep this in perspective.  We are replacing a read
      with a sequence of insns, but the read will almost certainly be
      in cache, so it is not going to be an expensive one.  Thus, we
      are not willing to do a multi insn shift or worse a subroutine
      call to get rid of the read.  */
+  if (dump_file)
+    fprintf (dump_file, "trying to replace %smode load in insn %d"
+	     " from %smode store in insn %d\n",
+	     GET_MODE_NAME (read_mode), INSN_UID (read_insn->insn),
+	     GET_MODE_NAME (store_mode), INSN_UID (store_insn->insn));
+  start_sequence ();
   if (shift)
+    read_reg = find_shift_sequence (access_size, store_info, read_info, shift);
+  else
+    read_reg = extract_low_bits (read_mode, store_mode,
+				 copy_rtx (store_info->rhs));
+  if (read_reg == NULL_RTX)
     {
-      if (access_size > UNITS_PER_WORD)
-	return false;
-
-      shift_seq = find_shift_sequence (read_reg, access_size, store_info,
-				       read_info, shift);
-      if (!shift_seq)
-	return false;
+      end_sequence ();
+      if (dump_file)
+	fprintf (dump_file, " -- could not extract bits of stored value\n");
+      return false;
     }
-
-  if (dump_file)
-    fprintf (dump_file, "replacing load at %d from store at %d\n",
-	     INSN_UID (read_insn->insn), INSN_UID (store_insn->insn)); 
+  /* Force the value into a new register so that it won't be clobbered
+     between the store and the load.  */
+  read_reg = copy_to_mode_reg (read_mode, read_reg);
+  insns = get_insns ();
+  end_sequence ();
 
   if (validate_change (read_insn->insn, loc, read_reg, 0))
     {
-      rtx insns;
       deferred_change_t deferred_change = pool_alloc (deferred_change_pool);
       
-      if (read_mode == store_mode)
-	{
-	  start_sequence ();
-	  
-	  /* The modes are the same and everything lines up.  Just
-	     generate a simple move.  */
-	  emit_move_insn (read_reg, store_info->rhs);
-	  if (dump_file)
-	    fprintf (dump_file, " -- adding move insn r%d = r%d\n",
-		     REGNO (read_reg), REGNO (store_info->rhs));
-	  insns = get_insns ();
-	  end_sequence ();
-	}
-      else if (shift)
-	insns = shift_seq;
-      else
-	{
-	  /* The modes are different but the lsb are in the same
-	     place, we need to extract the value in the right from the
-	     rhs of the store.  */
-	  start_sequence ();
-	  convert_move (read_reg, store_info->rhs, 1);
-	  
-	  if (dump_file)
-	    fprintf (dump_file, " -- adding extract insn r%d:%s = r%d:%s\n",
-		     REGNO (read_reg), GET_MODE_NAME (read_mode),
-		     REGNO (store_info->rhs), GET_MODE_NAME (store_mode));
-	  insns = get_insns ();
-	  end_sequence ();
-	}
-
       /* Insert this right before the store insn where it will be safe
 	 from later insns that might change it before the read.  */
       emit_insn_before (insns, store_insn->insn);
@@ -1668,12 +1637,22 @@ replace_read (store_info_t store_info, insn_info_t store_insn,
 	 rest of dse, play like this read never happened.  */
       read_insn->read_rec = read_info->next;
       pool_free (read_info_pool, read_info);
+      if (dump_file)
+	{
+	  fprintf (dump_file, " -- replaced the loaded MEM with ");
+	  print_simple_rtl (dump_file, read_reg);
+	  fprintf (dump_file, "\n");
+	}
       return true;
     }
   else 
     {
       if (dump_file)
-	fprintf (dump_file, " -- validation failure\n"); 
+	{
+	  fprintf (dump_file, " -- replacing the loaded MEM with ");
+	  print_simple_rtl (dump_file, read_reg);
+	  fprintf (dump_file, " led to an invalid instruction\n");
+	}
       return false;
     }
 }