PR 11319 analyzed (Re: Patch fixing 3.3 bug PR 9745 and PR 10021)

[David Edelsohn]

>>>>> Dale Johannesen writes:

Dale> It is not necessarily true that fixing the bug will introduce 
Dale> performance regressions.
Dale> If it is the case that the buggy code is moving some memory references 
Dale> out of
Dale> loops in cases where the compiler cannot tell that it is safe, and is 
Dale> getting lucky,
Dale> then yes, fixing the bug will cause regressions.  But I don't think we 
Dale> have
Dale> evidence of that.  (In practice, I mean - certainly that can happen in 
Dale> theory.)

	Compile the testcase from PR 9745 dumping out the GCC loop phase
with and without Jim's patch.  With Jim's patch about 2/3 of the
replaceable givs and Hoisted references disappear.  Those loop
transformations were partially more aggressive loop optimization as Jim
has suggested restoring and partially "getting lucky".

David