Bug 47790 - [4.5/4.6/4.7 Regression] optimize_bitfield_assignment_op no longer works in 4.5.x

Bug 47790 - [4.5/4.6/4.7 Regression] optimize_bitfield_assignment_op no longer works in 4.5.x

[Jeff Law]

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Andrew included a patch in this PR to make
optimize_bitfield_assignment_op work again.  I've fixed a couple
indention problems and added a couple comments.

Bootstrapped and regression tested on x86_64-unknown-linux-gnu.  Applied
to trunk.

Interestingly enough, it clearly helps the testcase referenced in the
PR, but doesn't help GCC itself or the runtime libraries.
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	PR middle-end/47790
	* expr.c (optimize_bitfield_assignment_op): Revamp to work
	again after expansion changes.


Index: expr.c
===================================================================
*** expr.c	(revision 171074)
--- expr.c	(working copy)
*************** optimize_bitfield_assignment_op (unsigne
*** 3974,3979 ****
--- 3974,3981 ----
    tree op0, op1;
    rtx value, result;
    optab binop;
+   gimple srcstmt;
+   enum tree_code code;
  
    if (mode1 != VOIDmode
        || bitsize >= BITS_PER_WORD
*************** optimize_bitfield_assignment_op (unsigne
*** 3983,3995 ****
      return false;
  
    STRIP_NOPS (src);
!   if (!BINARY_CLASS_P (src)
!       || TREE_CODE (TREE_TYPE (src)) != INTEGER_TYPE)
      return false;
  
!   op0 = TREE_OPERAND (src, 0);
!   op1 = TREE_OPERAND (src, 1);
!   STRIP_NOPS (op0);
  
    if (!operand_equal_p (to, op0, 0))
      return false;
--- 3985,4021 ----
      return false;
  
    STRIP_NOPS (src);
!   if (TREE_CODE (src) != SSA_NAME)
!     return false;
!   if (TREE_CODE (TREE_TYPE (src)) != INTEGER_TYPE)
!     return false;
! 
!   srcstmt = get_gimple_for_ssa_name (src);
!   if (!srcstmt
!       || TREE_CODE_CLASS (gimple_assign_rhs_code (srcstmt)) != tcc_binary)
      return false;
  
!   code = gimple_assign_rhs_code (srcstmt);
! 
!   op0 = gimple_assign_rhs1 (srcstmt);
! 
!   /* If OP0 is an SSA_NAME, then we want to walk the use-def chain
!      to find its initialization.  Hopefully the initialization will
!      be from a bitfield load.  */
!   if (TREE_CODE (op0) == SSA_NAME)
!     {
!       gimple op0stmt = get_gimple_for_ssa_name (op0);
! 
!       /* We want to eventually have OP0 be the same as TO, which
! 	 should be a bitfield.  */
!       if (!op0stmt
! 	  || !is_gimple_assign (op0stmt)
! 	  || gimple_assign_rhs_code (op0stmt) != TREE_CODE (to))
! 	return false;
!       op0 = gimple_assign_rhs1 (op0stmt);
!     }
! 
!   op1 = gimple_assign_rhs2 (srcstmt);
  
    if (!operand_equal_p (to, op0, 0))
      return false;
*************** optimize_bitfield_assignment_op (unsigne
*** 4026,4032 ****
    if (BYTES_BIG_ENDIAN)
      bitpos = str_bitsize - bitpos - bitsize;
  
!   switch (TREE_CODE (src))
      {
      case PLUS_EXPR:
      case MINUS_EXPR:
--- 4052,4058 ----
    if (BYTES_BIG_ENDIAN)
      bitpos = str_bitsize - bitpos - bitsize;
  
!   switch (code)
      {
      case PLUS_EXPR:
      case MINUS_EXPR:
*************** optimize_bitfield_assignment_op (unsigne
*** 4054,4060 ****
  	  set_mem_expr (str_rtx, 0);
  	}
  
!       binop = TREE_CODE (src) == PLUS_EXPR ? add_optab : sub_optab;
        if (bitsize == 1 && bitpos + bitsize != str_bitsize)
  	{
  	  value = expand_and (str_mode, value, const1_rtx, NULL);
--- 4080,4086 ----
  	  set_mem_expr (str_rtx, 0);
  	}
  
!       binop = code == PLUS_EXPR ? add_optab : sub_optab;
        if (bitsize == 1 && bitpos + bitsize != str_bitsize)
  	{
  	  value = expand_and (str_mode, value, const1_rtx, NULL);
*************** optimize_bitfield_assignment_op (unsigne
*** 4087,4093 ****
  	  set_mem_expr (str_rtx, 0);
  	}
  
!       binop = TREE_CODE (src) == BIT_IOR_EXPR ? ior_optab : xor_optab;
        if (bitpos + bitsize != GET_MODE_BITSIZE (GET_MODE (str_rtx)))
  	{
  	  rtx mask = GEN_INT (((unsigned HOST_WIDE_INT) 1 << bitsize)
--- 4113,4119 ----
  	  set_mem_expr (str_rtx, 0);
  	}
  
!       binop = code == BIT_IOR_EXPR ? ior_optab : xor_optab;
        if (bitpos + bitsize != GET_MODE_BITSIZE (GET_MODE (str_rtx)))
  	{
  	  rtx mask = GEN_INT (((unsigned HOST_WIDE_INT) 1 << bitsize)