i386.c (ix86_expand_clrmem): Move gen_cld down to the places where it is actually needed.

	* config/i386/i386.c (ix86_expand_clrmem): Move gen_cld down to
	the places where it is actually needed.  Don't use repz; stosb
	for -Os with sufficiently small constant sizes.
	For sufficiently small repz; stos{l,q} repeat counts use a sequence
	of stos{l,q} instructions instead.

From-SVN: r85635

gcc/ChangeLog

+2004-08-06  Jakub Jelinek  <jakub@redhat.com>
+
+	* config/i386/i386.c (ix86_expand_clrmem): Move gen_cld down to
+	the places where it is actually needed.  Don't use repz; stosb
+	for -Os with sufficiently small constant sizes.
+	For sufficiently small repz; stos{l,q} repeat counts use a sequence
+	of stos{l,q} instructions instead.
+
 2004-08-06  Zdenek Dvorak  <rakdver@atrey.karlin.mff.cuni.cz>
 
 	PR tree-optimization/16807

gcc/config/i386/i386.c

@@ -11508,13 +11508,20 @@ ix86_expand_clrmem (rtx dst, rtx count_exp, rtx align_exp)
   if (destreg != XEXP (dst, 0))
     dst = replace_equiv_address_nv (dst, destreg);
 
-  emit_insn (gen_cld ());
 
   /* When optimizing for size emit simple rep ; movsb instruction for
-     counts not divisible by 4.  */
+     counts not divisible by 4.  The movl $N, %ecx; rep; stosb
+     sequence is 7 bytes long, so if optimizing for size and count is
+     small enough that some stosl, stosw and stosb instructions without
+     rep are shorter, fall back into the next if.  */
 
-  if ((!optimize || optimize_size) && (count == 0 || (count & 0x03)))
+  if ((!optimize || optimize_size)
+      && (count == 0
+	  || ((count & 0x03)
+	      && (!optimize_size || (count & 0x03) + (count >> 2) > 7))))
     {
+      emit_insn (gen_cld ());
+
       countreg = ix86_zero_extend_to_Pmode (count_exp);
       zeroreg = copy_to_mode_reg (QImode, const0_rtx);
       destexp = gen_rtx_PLUS (Pmode, destreg, countreg);
@@ -11528,17 +11535,54 @@ ix86_expand_clrmem (rtx dst, rtx count_exp, rtx align_exp)
       int size = TARGET_64BIT && !optimize_size ? 8 : 4;
       unsigned HOST_WIDE_INT offset = 0;
 
+      emit_insn (gen_cld ());
+
       zeroreg = copy_to_mode_reg (size == 4 ? SImode : DImode, const0_rtx);
       if (count & ~(size - 1))
 	{
-	  countreg = copy_to_mode_reg (counter_mode,
-				       GEN_INT ((count >> (size == 4 ? 2 : 3))
-						& (TARGET_64BIT ? -1 : 0x3fffffff)));
-	  countreg = ix86_zero_extend_to_Pmode (countreg);
-	  destexp = gen_rtx_ASHIFT (Pmode, countreg, GEN_INT (size == 4 ? 2 : 3));
-	  destexp = gen_rtx_PLUS (Pmode, destexp, destreg);
-	  emit_insn (gen_rep_stos (destreg, countreg, dst, zeroreg, destexp));
-	  offset = count & ~(size - 1);
+	  unsigned HOST_WIDE_INT repcount;
+	  unsigned int max_nonrep;
+
+	  repcount = count >> (size == 4 ? 2 : 3);
+	  if (!TARGET_64BIT)
+	    repcount &= 0x3fffffff;
+
+	  /* movl $N, %ecx; rep; stosl is 7 bytes, while N x stosl is N bytes.
+	     movl $N, %ecx; rep; stosq is 8 bytes, while N x stosq is 2xN
+	     bytes.  In both cases the latter seems to be faster for small
+	     values of N.  */
+	  max_nonrep = size == 4 ? 7 : 4;
+	  if (!optimize_size)
+	    switch (ix86_tune)
+	      {
+	      case PROCESSOR_PENTIUM4:
+	      case PROCESSOR_NOCONA:
+	        max_nonrep = 3;
+	        break;
+	      default:
+	        break;
+	      }
+
+	  if (repcount <= max_nonrep)
+	    while (repcount-- > 0)
+	      {
+		rtx mem = adjust_automodify_address_nv (dst,
+							GET_MODE (zeroreg),
+							destreg, offset);
+		emit_insn (gen_strset (destreg, mem, zeroreg));
+		offset += size;
+	      }
+	  else
+	    {
+	      countreg = copy_to_mode_reg (counter_mode, GEN_INT (repcount));
+	      countreg = ix86_zero_extend_to_Pmode (countreg);
+	      destexp = gen_rtx_ASHIFT (Pmode, countreg,
+					GEN_INT (size == 4 ? 2 : 3));
+	      destexp = gen_rtx_PLUS (Pmode, destexp, destreg);
+	      emit_insn (gen_rep_stos (destreg, countreg, dst, zeroreg,
+				       destexp));
+	      offset = count & ~(size - 1);
+	    }
 	}
       if (size == 8 && (count & 0x04))
 	{