[Bug target/47764] The constant load instruction should be hoisted out of loop

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

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47764

Ramana Radhakrishnan <ramana at gcc dot gnu.org> changed:

           What    |Removed                     |Added
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                 CC|                            |ramana at gcc dot gnu.org

--- Comment #4 from Ramana Radhakrishnan <ramana at gcc dot gnu.org> 2011-08-10 22:17:23 UTC ---
(In reply to comment #3)
> > Any ideas of how this improvement could be implemented, Carrot?
> 
> The root cause of this problem is that arm/thumb store instruction can't
> directly store a immediate number to memory, but gcc doesn't realize this early
> enough. In most part of the rtl phase, the following form is kept.
> 
>   (insn 41 38 42 3 (set (mem:HI (plus:SI (reg/f:SI 169)
>                   (const_int 60 [0x3c])) [2 MEM[(struct deflate_state *)D.2085 
>   _3 + 60B]+0 S2 A16])
>           (const_int 0 [0])) src/trees.c:45 696 {*thumb2_movhi_insn}
>        (expr_list:REG_DEAD (reg/f:SI 169)
>           (nil)))
> 
> Until register allocation it finds the restriction of the store instruction and
> split it into two instructions, load 0 into register and store register to
> memory. But it's too late to do a loop optimization.

Eh, how is splitting this early going to help with hoisting this out of a loop
? 

Ramana