------- Comment #14 from ubizjak at gmail dot com 2010-06-10 15:12 ------- (In reply to comment #11)
> ADD is always faster than LEA for adding a register. However > there is a special case on Atom where ADD should be avoided. > It is true that LEA doesn't touch flags and we used it instead > of ADD which touches flags. It is an optimization specific for > Atom. You can think it as a special ADD for Atom and pretend > it clobbers flags. We shouldn't model it as a real LEA since > it is used to implement a faster ADD in this special case. LEA can also implement true three-operand add (rX = rY + rZ), so it can save a move. Expansion of three operands is effectively disabled due to usage of ix86_binary_operand_ok in PLUS patterns, so split to LEA certainly has some benefit. -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44470
