[Bug rtl-optimization/92602] New: Failure in gcc.target/powerpc/bswap64-2.c

[segher at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92602

            Bug ID: 92602
           Summary: Failure in gcc.target/powerpc/bswap64-2.c
           Product: gcc
           Version: 10.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: rtl-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: segher at gcc dot gnu.org
  Target Milestone: ---

r278509 exposes this problem (the -fno-common patch).  It causes global
variables to be accessed via an anchor.

But now fwprop1 does:

In insn 8, replacing
 (mem/c:DI (reg/f:DI 119) [1 ul+0 S8 A64])
 with (mem/c:DI (unspec:DI [
                (symbol_ref:DI ("*.LANCHOR0") [flags 0x182])
                (reg:DI 2 2)
            ] UNSPEC_TOCREL) [1 ul+0 S8 A64])

after which we have

(insn 6 3 8 2 (parallel [
            (set (reg:DI 117 [ _1 ])
                (bswap:DI (reg/v:DI 118 [ a ])))
            (clobber (scratch:DI))
            (clobber (scratch:DI))
        ]) "bswap64-2.c":10:45 156 {bswapdi2_reg}
     (expr_list:REG_DEAD (reg/v:DI 118 [ a ])
        (nil)))
(insn 8 6 0 2 (set (mem/c:DI (unspec:DI [
                    (symbol_ref:DI ("*.LANCHOR0") [flags 0x182])
                    (reg:DI 2 2)
                ] UNSPEC_TOCREL) [1 ul+0 S8 A64])
        (reg:DI 117 [ _1 ])) "bswap64-2.c":10:43 622 {*movdi_internal64}
     (expr_list:REG_DEAD (reg/f:DI 119)
        (expr_list:REG_DEAD (reg:DI 117 [ _1 ])
            (nil))))

and those can no longer be combined.  Before the change, combine would
combine the reg-reg bswap and the simple indirect store to a bswapping
store.