[Bug target/39942] Nonoptimal code - leaveq; xchg %ax,%ax; retq

["jakub at gcc dot gnu dot org" <gcc-bugzilla@gcc.gnu.org>]

------- Comment #37 from jakub at gcc dot gnu dot org  2009-05-15 07:56 -------
This patch looks very wrong.  It assumes that min_insn_size gives exact insn
sizes (current min_insn_size is very far from that, but even get_attr_length
isn't exact), doesn't take into account label alignments nor branch shortening
which can change the insn sizes afterwards and assumes that a p2align always
aligns to 16 bytes (it does not).
While the previous algorithm works with estimated 16 consecutive bytes rather
than 16 byte pages 0xXXXX0 ... 0xXXXF, that's because during machine reorg
you simply can't know in most cases where exactly the 16 byte page will start,
so you assume it can start (almost) anywhere (and use .p2align behavior to
align when needed).


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39942