Comment 24 for bug 836588

Note, can't be reproduced on the trunk, the strcmp isn't DCEd there, but guess the problem is just latent there.

It looks like a target bug to me. Before RTL loop opts we have:
(insn 91 90 92 13 (set (reg:SI 167)
        (unspec:SI [
                (const:SI (unspec:SI [
                            (symbol_ref/v/f:SI ("*.LC4") [flags 0x82] <var_decl 0x7f5ebb0a5500 *.LC4>)
                            (const:SI (plus:SI (unspec:SI [
                                            (const_int 4 [0x4])
                                        ] 21)
                                    (const_int 8 [0x8])))
                        ] 27))
            ] 3)) pr48308.i:228 170 {pic_load_addr_32bit}
     (nil))

(insn 92 91 94 13 (set (reg:SI 167)
        (unspec:SI [
                (reg:SI 167)
                (const_int 8 [0x8])
                (const_int 4 [0x4])
            ] 4)) pr48308.i:228 173 {pic_add_dot_plus_eight}
     (expr_list:REG_EQUAL (symbol_ref/v/f:SI ("*.LC4") [flags 0x82] <var_decl 0x7f5ebb0a5500 *.LC4>)
        (nil)))

and the pseudo 167 is then used to load one of the strcmp parameters.
Then (probably loop invariant motion) moves insn 91 before the loop, as it looks to be loop invariant, but insn 92 is kept in the loop.
Next during RA, the register pressure is high and thus pseudo 167 is spilled, so
before the loop there is a store. Then during the *.csa pass DCE is performed and the strcmp is removed, which means insn 92 is removed as well, but the store before the loop of course is kept. And there is no further DSE pass that would optimize that (now dead) store away.
So, IMHO arm_reorg needs to handle this case, find out what minipool entries don't have the corresponding UNSPEC_PIC_BASE insn and handle them somehow (either by emitting there a dummy 0 or similar, or trying to replace the insn with UNSPEC_PIC_SYM with something else, ...).
That said, perhaps it would be nice to help the loop optimizers somehow figure out that even the UNSPEC_PIC_BASE is loop invariant (wrap it into CONST?).