This is the mail archive of the mailing list for the GCC project.

Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]
Other format: [Raw text]

Re: Missed optimization in PRE?

On Thu, Mar 29, 2012 at 6:14 PM, Richard Guenther
<> wrote:
> On Thu, Mar 29, 2012 at 12:10 PM, Bin.Cheng <> wrote:
>> On Thu, Mar 29, 2012 at 6:07 PM, Richard Guenther
>> <> wrote:
>>> On Thu, Mar 29, 2012 at 12:02 PM, Bin.Cheng <> 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.

Best Regards.

Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]