[PATCH] Fix part of PR42587

[Richard Biener <rguenther at suse dot de>]

The recent subreg-CSE allows a part of PR42587 to be fixed with
minimal surgery to the bswap pass - namely adding support for
BIT_FIELD_REF.

Bootstrapped and tested on x86_64-unknown-linux-gnu, applied to trunk.

Richard.

2016-05-13  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/42587
	* tree-ssa-math-opts.c (perform_symbolic_merge): Handle BIT_FIELD_REF.
	(find_bswap_or_nop_1): Likewise.
	(bswap_replace): Likewise.

	* gcc.dg/optimize-bswapsi-4.c: New testcase.

Index: gcc/tree-ssa-math-opts.c
===================================================================
*** gcc/tree-ssa-math-opts.c	(revision 236159)
--- gcc/tree-ssa-math-opts.c	(working copy)
*************** perform_symbolic_merge (gimple *source_s
*** 2160,2168 ****
    gimple *source_stmt;
    struct symbolic_number *n_start;
  
    /* Sources are different, cancel bswap if they are not memory location with
       the same base (array, structure, ...).  */
!   if (gimple_assign_rhs1 (source_stmt1) != gimple_assign_rhs1 (source_stmt2))
      {
        uint64_t inc;
        HOST_WIDE_INT start_sub, end_sub, end1, end2, end;
--- 2160,2175 ----
    gimple *source_stmt;
    struct symbolic_number *n_start;
  
+   tree rhs1 = gimple_assign_rhs1 (source_stmt1);
+   if (TREE_CODE (rhs1) == BIT_FIELD_REF)
+     rhs1 = TREE_OPERAND (rhs1, 0);
+   tree rhs2 = gimple_assign_rhs1 (source_stmt2);
+   if (TREE_CODE (rhs2) == BIT_FIELD_REF)
+     rhs2 = TREE_OPERAND (rhs2, 0);
+ 
    /* Sources are different, cancel bswap if they are not memory location with
       the same base (array, structure, ...).  */
!   if (rhs1 != rhs2)
      {
        uint64_t inc;
        HOST_WIDE_INT start_sub, end_sub, end1, end2, end;
*************** find_bswap_or_nop_1 (gimple *stmt, struc
*** 2285,2290 ****
--- 2292,2330 ----
    if (find_bswap_or_nop_load (stmt, rhs1, n))
      return stmt;
  
+   /* Handle BIT_FIELD_REF.  */
+   if (TREE_CODE (rhs1) == BIT_FIELD_REF
+       && TREE_CODE (TREE_OPERAND (rhs1, 0)) == SSA_NAME)
+     {
+       unsigned HOST_WIDE_INT bitsize = tree_to_uhwi (TREE_OPERAND (rhs1, 1));
+       unsigned HOST_WIDE_INT bitpos = tree_to_uhwi (TREE_OPERAND (rhs1, 2));
+       if (bitpos % BITS_PER_UNIT == 0
+ 	  && bitsize % BITS_PER_UNIT == 0
+ 	  && init_symbolic_number (n, TREE_OPERAND (rhs1, 0)))
+ 	{
+ 	  /* Shift.  */
+ 	  if (!do_shift_rotate (RSHIFT_EXPR, n, bitpos))
+ 	    return NULL;
+ 
+ 	  /* Mask.  */
+ 	  uint64_t mask = 0;
+ 	  uint64_t tmp = (1 << BITS_PER_UNIT) - 1;
+ 	  for (unsigned i = 0; i < bitsize / BITS_PER_UNIT;
+ 	       i++, tmp <<= BITS_PER_UNIT)
+ 	    mask |= (uint64_t) MARKER_MASK << (i * BITS_PER_MARKER);
+ 	  n->n &= mask;
+ 
+ 	  /* Convert.  */
+ 	  n->type = TREE_TYPE (rhs1);
+ 	  if (!n->base_addr)
+ 	    n->range = TYPE_PRECISION (n->type) / BITS_PER_UNIT;
+ 
+ 	  return verify_symbolic_number_p (n, stmt) ? stmt : NULL;
+ 	}
+ 
+       return NULL;
+     }
+ 
    if (TREE_CODE (rhs1) != SSA_NAME)
      return NULL;
  
*************** bswap_replace (gimple *cur_stmt, gimple
*** 2683,2688 ****
--- 2723,2730 ----
  	}
        src = val_tmp;
      }
+   else if (TREE_CODE (src) == BIT_FIELD_REF)
+     src = TREE_OPERAND (src, 0);
  
    if (n->range == 16)
      bswap_stats.found_16bit++;
Index: gcc/testsuite/gcc.dg/optimize-bswapsi-4.c
===================================================================
*** gcc/testsuite/gcc.dg/optimize-bswapsi-4.c	(revision 0)
--- gcc/testsuite/gcc.dg/optimize-bswapsi-4.c	(working copy)
***************
*** 0 ****
--- 1,28 ----
+ /* { dg-do compile } */
+ /* { dg-require-effective-target bswap32 } */
+ /* { dg-options "-O2 -fdump-tree-bswap" } */
+ /* { dg-additional-options "-march=z900" { target s390-*-* } } */
+ 
+ typedef unsigned char u8;
+ typedef unsigned int u32;
+ union __anonunion
+ {
+   u32 value;
+   u8 bytes[4];
+ };
+ 
+ u32
+ acpi_ut_dword_byte_swap (u32 value)
+ {
+   union __anonunion in;
+   in.value = value;
+ #if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
+   return ((in.bytes[0] << 24) | (in.bytes[1] << 16)
+ 	  | (in.bytes[2] << 8) | in.bytes[3]);
+ #else
+   return ((in.bytes[3] << 24) | (in.bytes[2] << 16)
+ 	  | (in.bytes[1] << 8) | in.bytes[0]);
+ #endif
+ }
+ 
+ /* { dg-final { scan-tree-dump "32 bit bswap implementation found at" "bswap" } } */