On Mon, Mar 12, 2012 at 11:13 AM, Paolo Bonzini <bonz...@gnu.org> wrote: > Il 12/03/2012 09:52, Uros Bizjak ha scritto: >> +(define_peephole2 >> + [(parallel [(set (reg FLAGS_REG) (match_operand 0 "" "")) >> + (match_operand 4 "" "")]) >> + (set (match_operand:QI 1 "register_operand" "") >> + (match_operator:QI 2 "ix86_comparison_operator" >> + [(reg FLAGS_REG) (const_int 0)])) >> + (set (match_operand 3 "q_regs_operand" "") >> + (zero_extend (match_dup 1)))] >> + "(peep2_reg_dead_p (3, operands[1]) >> + || operands_match_p (operands[1], operands[3])) >> + && ! reg_overlap_mentioned_p (operands[3], operands[0])" > > I understand that you're assuming the shape of operands[4] to be the > same as operands[3], but would it be preferrable to add another overlap > check on operands[4]? > > For example the transformation is invalid if you had an overlap between > operands[3] and the destination of operands[4].
The destination of operands[4] _always_ matches one of operands inside operand[0]. All arithmetic insn that set flags are destructive on x86. Uros.
