[Bug rtl-optimization/43286] Missed related value optimization in cse.c

[carrot at google dot com]

------- Comment #5 from carrot at google dot com  2010-03-18 03:52 -------
In this case arm_arm_address_cost does the right thing. The problem is in
function should_replace_address.

When two addresses have same address cost, we choose the one with higher rtx
cost. The reason is "That has the potential of eliminating the most insns
without additional costs". But when two addresses have the same rtx cost, they
also have the potential to eliminate a previous definition. Just as
demonstrated by this test case.

One of the candidate is

old_rtx
(plus:SI (reg/v/f:SI 133 [ saveArea ])
    (const_int 8 [0x8]))

new_rtx
(plus:SI (reg/v/f:SI 140 [ fp ])
    (const_int -8 [0xfffffffffffffff8]))

After all of these addresses being replaced, instruction A can be removed.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43286