On Thu, Mar 29, 2012 at 5:25 PM, Bin.Cheng <amker.ch...@gmail.com> wrote: > On Thu, Mar 29, 2012 at 6:14 PM, Richard Guenther > <richard.guent...@gmail.com> wrote: >> On Thu, Mar 29, 2012 at 12:10 PM, Bin.Cheng <amker.ch...@gmail.com> wrote: >>> On Thu, Mar 29, 2012 at 6:07 PM, Richard Guenther >>> <richard.guent...@gmail.com> wrote: >>>> On Thu, Mar 29, 2012 at 12:02 PM, Bin.Cheng <amker.ch...@gmail.com> wrote: >>>>> Hi, >>>>> Following is the tree dump of 094t.pre for a test program. >>>>> Question is loads of D.5375_12/D.5375_14 are redundant on path <bb2, >>>>> bb7, bb5, bb6>, >>>>> but why not lowered into basic block 3, where it is used. >>>>> >>>>> BTW, seems no tree pass handles this case currently. >>>> >>>> tree-ssa-sink.c should do this. >>>> >>> It does not work for me, I will double check and update soon. >> >> Well, "should" as in, it's the place to do it. And certainly the pass can >> sink >> loads, so this must be a missed optimization. >> > Curiously, it is said explicitly that "We don't want to sink loads from > memory." > in tree-ssa-sink.c function statement_sink_location, and the condition is > > if (stmt_ends_bb_p (stmt) > || gimple_has_side_effects (stmt) > || gimple_has_volatile_ops (stmt) > || (gimple_vuse (stmt) && !gimple_vdef (stmt)) > <-----------------check load > || (cfun->has_local_explicit_reg_vars > && TYPE_MODE (TREE_TYPE (gimple_assign_lhs (stmt))) == BLKmode)) > return false; > > I haven't found any clue about this decision in ChangeLogs.
Ah, that's probably because usually you want to hoist loads and sink stores, separating them (like a scheduler would do). We'd want to restrict sinking of loads to sink into not post-dominated regions (thus where they end up being executed less times). Richard. > > -- > Best Regards.
