------- Comment #7 from ramana dot radhakrishnan at codito dot com 2006-10-09 16:33 ------- (In reply to comment #5)
flow.c is responsible for generating POST_INCs and POST_MODIFY's in 3.4 / 4.0 / 4.1 / 4.2 . I believe this is being replaced by the new data flow bits in the data flow branch. This might not be ready until 4.3 . We have hit similar issues in a private port that I maintain. 2 options are either to fix flow.c or use some of Joern's auto increment patches for 4.1 / 4.2 to fix this issue. This doesn't really take care of POST_MODIFY but I don't think that affects ARM that much. > Here's what's going on in this case: > > CSE changes an address if: > A) The cost of the address is lower > or > B) The cost of the address is the same and the cost of the RTX would be > higher outside of an address > > So, CSE changes (R) to (R+4) because it is lower cost as specified by the > address_costs hook. > > It doesn't change beyond (R+4) because (R+8) is the same cost as (R+4). > > Once the address (R+4) gets in the RTL sequence, it never gets converted to > a postincrement form. > > So by adding the cost of a simple REG RTX as being lower than (+ (REG) > (CONST)) > in the addressing modes, CSE doesn't convert the address to base+offset, and > we get the postincrement code back again in 4.x. > -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29294
