------- Comment #30 from bergner at vnet dot ibm dot com 2006-12-05 04:22
-------
Ok, the problem from comment #28 was due to a latent bug in
reload1.c:eliminate_regs_in_insn(). The bug is that eliminate_regs_in_insn()
calls single_set() on the passed in insn. This has been fine before, but now
with the patch, we end up passing in a parallel insn for a load with update and
the load portion of the parallel has the REG_UNUSED flag set. This causes
single_set() to return the "update" portion of the parallel instead of
returning NULL as it would do normally with parallels. This causes us to only
eliminate the update portion of the parallel and we skip eliminating the load
portion. The problem insn belfore eliminate_regs_in_insn() looks like:
(insn 12 62 13 2 (parallel [
(set (reg:SI 0 0 [125])
(mem/s/j:SI (plus:SI (reg/f:SI 113 sfp)
(const_int 8 [0x8])) [0 S4 A32]))
(set (reg/f:SI 9 9 [orig:124 D.965 ] [124])
(plus:SI (reg/f:SI 113 sfp)
(const_int 8 [0x8])))
]) 373 {*movsi_update1} (nil)
(expr_list:REG_UNUSED (reg:SI 0 0 [125])
(nil)))
After eliminate_regs_in_insn(), we have:
(insn 12 62 13 2 (parallel [
(set (reg:SI 0 0 [125])
(mem/s/j:SI (plus:SI (reg/f:SI 113 sfp)
(const_int 8 [0x8])) [0 S4 A32]))
(set (reg/f:SI 9 9 [orig:124 D.965 ] [124])
(plus:SI (reg/f:SI 1 1)
(const_int 8 [0x8])))
]) 373 {*movsi_update1} (nil)
(expr_list:REG_UNUSED (reg:SI 0 0 [125])
(nil)))
However, calculate_needs_all_insns() ends up backing out the eliminated
(reg/f:SI 1 1) with the non eliminated (reg/f:SI 113 sfp) and (reg/f:SI 113
sfp) never gets eliminated after that and we generate bogus assembler.
In addition to the latest patch attached here, I added the following patch to
stop eliminate-regs_in_insn from calling single_set for parallel insns. It
fixed the bug here and bootstrapped and regtested with no errors. I'll post
the combined patch to gcc-patches.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28690
