------- Comment #4 from carrot at google dot com 2009-07-14 09:14 ------- In TREE level, the two stores are different statements. Only after register allocation, the two stores get same register and make the load redundant.
try_crossjump_bb tries to find same instruction sequence in all predecessors of a basic block bb, and move that code sequence to head of bb. It is triggered by this function, and the store is moved just before the load. I tried -fgcse-las but it couldn't do the work. (In reply to comment #2) > -fgcse-las should do the trick. Note that PRE would do this kind of > optimization on the tree-level, but it is disabled with -Os (so is gcse). > > <bb 2>: > D.1614_2 = p2_1(D)->front; > p1_3(D)->head = D.1614_2; > goto <bb 4>; > > <bb 3>: > D.1616_8 = D.1615_4->next; > p1_3(D)->head = D.1616_8; > > <bb 4>: > D.1615_4 = p1_3(D)->head; > -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40730
