[Bug rtl-optimization/80818] LRA clobbers live hard reg clobbered during rematerialization

[krebbel at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80818

--- Comment #4 from Andreas Krebbel <krebbel at gcc dot gnu.org> ---
Created attachment 41609
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=41609&action=edit
Reduced testcase

gcc -O3 -march=z900 t.c

r33 is marked as unused in process_bb_lives for the compare (insn 10), although
the value is used by the add with carry (insn 18).

(insn 10 23 24 2 (parallel [
            (set (reg:CCL3 33 %cc)
                (compare:CCL3 (reg/v:DI 73 [orig:64 a ] [64])
                    (reg/v:DI 65 [ b ])))
            (clobber (reg/v:DI 73 [orig:64 a ] [64]))
        ]) "t.c":6 1632 {*subdi3_cconly2}
     (expr_list:REG_UNUSED (reg:CC 33 %cc)
        (expr_list:REG_UNUSED (reg/v:DI 73 [orig:64 a ] [64])
            (expr_list:REG_DEAD (reg/v:DI 65 [ b ])
                (nil)))))