[PATCH] lower-subreg: Decompose multiword shifts and zero-extends

[PATCH] lower-subreg: Decompose multiword shifts and zero-extends

[Andreas Krebbel]

Hello,

here is an enhanced version of my decompose multiword shifts patch.

This version also deals with multiword zero-extends of wordmode
pseudos as suggested by Ulrich and with more than word wide shifts as
suggested by Paolo.

Handling zero-extends as well fixes also the problem Rask were seeing
on i386:

With the new patch and -O2 -march=k6 -m32 I get (for the first
function of the attached testcase):

foo:
        pushl   %ebp
        movl    %esp, %ebp
        movl    12(%ebp), %eax
        movl    8(%ebp), %edx
        leave
        ret

instead of (without any patch):

foo:
	pushl	%ebp		# 39	*pushsi2	[length = 1]
	movl	%esp, %ebp	# 40	*movsi_1/1	[length = 2]
	movl	8(%ebp), %edx	# 37	*movsi_1/1	[length = 3]
	movl	12(%ebp), %eax	# 10	*movsi_1/1	[length = 3]
	leave			# 43	leave	[length = 1]
	movl	%edx, %ecx	# 46	*movsi_1/1	[length = 2]
	movl	%ecx, %edx	# 11	*movsi_1/1	[length = 2]
	ret			# 44	return_internal	[length = 1]

So there is also a small improvement here.

Bootstrapped on s390, s390x, i686 and x86_64.
No testsuite regressions.

Ok for mainline?

Bye,

-Andreas-



2007-08-06  Andreas Krebbel  <krebbel1@de.ibm.com>

	* lower-subreg.c (resolve_subreg_use): Remove assertion.
	(find_decomposable_shift_zeroextend,
	resolve_shift_zeroextend): New functions.
	(decompose_multiword_subregs): Use the functions above to decompose
	multiword shifts and zero-extends.


Index: gcc/lower-subreg.c
===================================================================
*** gcc/lower-subreg.c.orig	2007-08-06 10:56:55.000000000 +0200
--- gcc/lower-subreg.c	2007-08-06 14:34:01.000000000 +0200
*************** resolve_subreg_use (rtx *px, void *data)
*** 525,532 ****
      {
        /* Return 1 to the caller to indicate that we found a direct
  	 reference to a register which is being decomposed.  This can
! 	 happen inside notes.  */
!       gcc_assert (!insn);
        return 1;
      }
  
--- 525,531 ----
      {
        /* Return 1 to the caller to indicate that we found a direct
  	 reference to a register which is being decomposed.  This can
! 	 happen inside notes or multiword shift instructions.  */
        return 1;
      }
  
*************** resolve_use (rtx pat, rtx insn)
*** 944,949 ****
--- 943,1105 ----
    return false;
  }
  
+ /* Checks if INSN is a decomposable multiword-shift or zero-extend and
+    sets the decomposable_context bitmap accordingly.  A non-zero value
+    is returned if a decomposable insn has been found.  */
+ 
+ static int
+ find_decomposable_shift_zeroextend (rtx insn)
+ {
+   rtx set;
+   rtx op;
+   rtx op_operand;
+ 
+   set = single_set (insn);
+   if (!set)
+     return 0;
+ 
+   op = SET_SRC (set);
+   if (GET_CODE (op) != ASHIFT
+       && GET_CODE (op) != LSHIFTRT
+       && GET_CODE (op) != ZERO_EXTEND)
+     return 0;
+ 
+   op_operand = XEXP (op, 0);
+   if (!REG_P (SET_DEST (set)) || !REG_P (op_operand)
+       || HARD_REGISTER_NUM_P (REGNO (SET_DEST (set)))
+       || HARD_REGISTER_NUM_P (REGNO (op_operand))
+       || !SCALAR_INT_MODE_P (GET_MODE (op)))
+     return 0;
+ 
+   if (GET_CODE (op) == ZERO_EXTEND)
+     {
+       if (GET_MODE (op_operand) != word_mode
+ 	  || GET_MODE_BITSIZE (GET_MODE (op)) != 2 * BITS_PER_WORD)
+ 	return 0;
+     }
+   else /* left or right shift */
+     {
+       if (GET_CODE (XEXP (op, 1)) != CONST_INT
+ 	  || INTVAL (XEXP (op, 1)) < BITS_PER_WORD
+ 	  || GET_MODE_BITSIZE (GET_MODE (op_operand)) != 2 * BITS_PER_WORD)
+ 	return 0;
+     }
+ 
+   bitmap_set_bit (decomposable_context, REGNO (SET_DEST (set)));
+ 
+   if (GET_CODE (op) != ZERO_EXTEND)
+     bitmap_set_bit (decomposable_context, REGNO (op_operand));
+ 
+   return 1;
+ }
+ 
+ /* Decompose a 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.  */
+ 
+ static rtx
+ resolve_shift_zeroextend (rtx insn)
+ {
+   rtx set;
+   rtx op;
+   rtx op_operand;
+   rtx insns;
+   rtx src_reg, dest_reg, dest_zero;
+   int src_reg_num, dest_reg_num, offset1, offset2, src_offset;
+ 
+   set = single_set (insn);
+   if (!set)
+     return NULL_RTX;
+ 
+   op = SET_SRC (set);
+   if (GET_CODE (op) != ASHIFT
+       && GET_CODE (op) != LSHIFTRT
+       && GET_CODE (op) != ZERO_EXTEND)
+     return NULL_RTX;
+ 
+   op_operand = XEXP (op, 0);
+ 
+   if (!resolve_reg_p (SET_DEST (set)) && !resolve_reg_p (op_operand))
+     return NULL_RTX;
+ 
+   /* src_reg_num is the number of the word mode register which we
+      are operating on.  For a left shift and a zero_extend on little
+      endian machines this is register 0.  */
+   src_reg_num = GET_CODE (op) == LSHIFTRT ? 1 : 0;
+ 
+   if (WORDS_BIG_ENDIAN)
+     src_reg_num = 1 - src_reg_num;
+ 
+   if (GET_CODE (op) == ZERO_EXTEND)
+     dest_reg_num = src_reg_num;
+   else
+     dest_reg_num = 1 - src_reg_num;
+ 
+   offset1 = UNITS_PER_WORD * dest_reg_num;
+   offset2 = UNITS_PER_WORD * (1 - dest_reg_num);
+   src_offset = UNITS_PER_WORD * src_reg_num;
+  
+   if (WORDS_BIG_ENDIAN != BYTES_BIG_ENDIAN)
+     {
+       offset1 += UNITS_PER_WORD - 1;
+       offset2 += UNITS_PER_WORD - 1;
+       src_offset += UNITS_PER_WORD - 1;
+     }
+ 
+   start_sequence ();
+ 
+   if (resolve_reg_p (SET_DEST (set)))
+     {
+       gcc_assert (GET_CODE (SET_DEST (set)) == CONCATN);
+ 
+       dest_reg = XVECEXP (SET_DEST (set), 0, dest_reg_num);
+       dest_zero = XVECEXP (SET_DEST (set), 0, 1 - dest_reg_num);
+     }
+   else
+     {
+       dest_reg = gen_rtx_SUBREG (word_mode, SET_DEST (set), offset1);
+       dest_zero = gen_rtx_SUBREG (word_mode, SET_DEST (set), offset2);
+     }
+ 
+   if (resolve_reg_p (op_operand))
+     {
+       gcc_assert (GET_CODE (op_operand) == CONCATN);
+ 
+       src_reg = XVECEXP (op_operand, 0, src_reg_num);
+     }
+   else
+     src_reg = gen_rtx_SUBREG (word_mode, op_operand, src_offset);
+ 
+   if (GET_CODE (op) != ZERO_EXTEND)
+     {
+       int shift_count = INTVAL (XEXP (op, 1));
+       if (shift_count > BITS_PER_WORD)
+ 	src_reg = expand_shift (GET_CODE (op) == ASHIFT ?
+ 				LSHIFT_EXPR : RSHIFT_EXPR,
+ 				word_mode, src_reg,
+ 				build_int_cst (NULL_TREE,
+ 					       shift_count - BITS_PER_WORD),
+ 				dest_reg, 1);
+     }
+ 
+   if (dest_reg != src_reg)
+     emit_move_insn (dest_reg, src_reg);
+   emit_move_insn (dest_zero, CONST0_RTX (word_mode));
+   insns = get_insns ();
+ 
+   end_sequence ();
+ 
+   emit_insn_before (insns, insn);
+ 
+   if (dump_file)
+     fprintf (dump_file, "; Replacing insn: %d with insns: %d and %d\n",
+ 	     INSN_UID (insn), INSN_UID (insns), INSN_UID (NEXT_INSN (insns)));
+ 
+   delete_insn (insn);
+   return insns;
+ }
+ 
  /* Look for registers which are always accessed via word-sized SUBREGs
     or via copies.  Decompose these registers into several word-sized
     pseudo-registers.  */
*************** decompose_multiword_subregs (void)
*** 1003,1008 ****
--- 1159,1167 ----
  	      || GET_CODE (PATTERN (insn)) == USE)
  	    continue;
  
+ 	  if (find_decomposable_shift_zeroextend (insn))
+ 	    continue;
+ 
  	  recog_memoized (insn);
  	  extract_insn (insn);
  
*************** decompose_multiword_subregs (void)
*** 1152,1157 ****
--- 1311,1329 ----
  			    SET_BIT (sub_blocks, bb->index);
  			}
  		    }
+ 		  else
+ 		    {
+ 		      rtx decomposed_shift;
+ 
+ 		      decomposed_shift = resolve_shift_zeroextend (insn);
+ 		      if (decomposed_shift != NULL_RTX)
+ 			{
+ 			  changed = true;
+ 			  insn = decomposed_shift;
+ 			  recog_memoized (insn);
+ 			  extract_insn (insn);
+ 			}
+ 		    }
  
  		  for (i = recog_data.n_operands - 1; i >= 0; --i)
  		    for_each_rtx (recog_data.operand_loc[i],
Index: gcc/testsuite/gcc.dg/multiword-1.c
===================================================================
*** /dev/null	1970-01-01 00:00:00.000000000 +0000
--- gcc/testsuite/gcc.dg/multiword-1.c	2007-08-06 10:57:17.000000000 +0200
***************
*** 0 ****
--- 1,67 ----
+ /* { dg-do run } */
+ /* { dg-options "-O3" } */
+ 
+ typedef unsigned int u32;
+ typedef unsigned long long u64;
+ 
+ u64 __attribute__((noinline))
+ foo (u32 high, u32 low)
+ {
+   return ((u64)high << 32) | low;
+ }
+ 
+ u32 __attribute__((noinline))
+ right (u64 t)
+ {
+   return (u32)(t >> 32);
+ }
+ 
+ u64 __attribute__((noinline))
+ left (u32 t)
+ {
+   return (u64)t << 32;
+ }
+ 
+ u32 __attribute__((noinline))
+ right2 (u64 t)
+ {
+   return (u32)(t >> 40);
+ }
+ 
+ u64 __attribute__((noinline))
+ left2 (u32 t)
+ {
+   return (u64)t << 40;
+ }
+ 
+ u64 __attribute__((noinline))
+ zeroextend (u32 t)
+ {
+   return (u64)t;
+ }
+ 
+ extern void abort ();
+ 
+ int
+ main ()
+ {
+   if (foo (13000, 12000) != 55834574860000ULL)
+     abort ();
+ 
+   if (right (55834574860000ULL) != 13000)
+     abort ();
+ 
+   if (left (13000) != 55834574848000ULL)
+     abort ();
+ 
+   if (right2 (55834574860000ULL) != 50)
+     abort ();
+ 
+   if (left2 (13000) != 14293651161088000ULL)
+     abort ();
+ 
+   if (zeroextend (13000) != 13000ULL)
+     abort ();
+ 
+   return 0;
+ }

Re: [PATCH] lower-subreg: Decompose multiword shifts and zero-extends

[Paolo Bonzini]

> 	* lower-subreg.c (resolve_subreg_use): Remove assertion.
> 	(find_decomposable_shift_zeroextend,
> 	resolve_shift_zeroextend): New functions.

Simple naming issue: I would call the function 
find_decomposable_shift_or_zext and resolve_shift_or_zext (see current 
uses in double_int_zext and zext_optab).

Paolo