On Jan 16, 2013, Richard Henderson <r...@redhat.com> wrote: > I notice that these expressions (including the first hunk that uses > ifs) are now all the same.
*nod* > It would seem extremely prudent to pull > this out to a function so that they stay the same. ack, will do. > That said, I question the change of <= to == 0. If negative, we don't > know how much overlap there is as far as I can see. Why not? Since the addresses are constants, and the negative sizes are just the adjusted sizes, negated to indicate they were conservatively lengthened by an alignment operation, we can determine that two references don't overlap if they're far enough from each other that, even with the alignment adjustment, they're still clearly non-overlapping. Say, if x is 0x0fff and y is 0x1234, both originally referenced with size 8 and x aligned to 0x20, it is obvious that the accesses won't overlap, in spite of the alignment on x. The test applied on constant addresses wouldn't realize that and would say they could overlap, because any alignment-adjusted size would be mistaken as “overlaps with anything”. >> if (GET_CODE (x) == CONST) >> @@ -2139,7 +2141,8 @@ memrefs_conflict_p (int xsize, rtx x, int ysize, rtx >> y, HOST_WIDE_INT c) >> if (CONSTANT_P (y)) >> return (xsize <= 0 || ysize <= 0 >> || (rtx_equal_for_memref_p (x, y) >> - && ((c >= 0 && xsize > c) || (c < 0 && ysize+c > 0)))); >> + && ((c >= 0 && abs (xsize) - c > 0) >> + || (c < 0 && abs (ysize) + c > 0)))); > This hunk is not needed, as we begin by eliminating <= 0. So the abs > is certain to do nothing. The function I'll introduce to keep the expressions the same will have the abs and I'll use it here, but you're right that after testing for negative sizes they abses won't make much of a difference. -- Alexandre Oliva, freedom fighter http://FSFLA.org/~lxoliva/ You must be the change you wish to see in the world. -- Gandhi Be Free! -- http://FSFLA.org/ FSF Latin America board member Free Software Evangelist Red Hat Brazil Compiler Engineer
