[Bug target/58945] Improve atomic_compare_and_swap*_doubleword pattern

[ubizjak at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58945

--- Comment #5 from Uroš Bizjak <ubizjak at gmail dot com> ---
Created attachment 33744
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=33744&action=edit
Simplified patch

Somehow simplified patch for mainline. Still fails with -O2 -mcx16:

atomic-store-6.c: In function ‘main’:
atomic-store-6.c:13:1: error: unable to find a register to spill
 }
 ^
atomic-store-6.c:13:1: error: this is the insn:
(insn 9 48 47 3 (parallel [
            (set (reg:TI 101 [86])
                (unspec_volatile:TI [
                        (mem/v:TI (symbol_ref:DI ("i")  <var_decl
0x2adae9631c60 i>) [-1  S16 A128])
                        (reg:TI 101 [86])
                        (reg:DI 102 [99])
                        (reg:DI 99)
                        (const_int 5 [0x5])
                    ] UNSPECV_CMPXCHG))
            (set (mem/v:TI (symbol_ref:DI ("i")  <var_decl 0x2adae9631c60 i>)
[-1  S16 A128])
                (unspec_volatile:TI [
                        (const_int 0 [0])
                    ] UNSPECV_CMPXCHG))
            (set (reg:CCZ 17 flags)
                (unspec_volatile:CCZ [
                        (const_int 0 [0])
                    ] UNSPECV_CMPXCHG))
        ]) atomic-store-6.c:9 4876 {atomic_compare_and_swapti_doubleword}
     (expr_list:REG_DEAD (reg:DI 102 [99])
        (nil)))
atomic-store-6.c:13:1: internal compiler error: in assign_by_spills, at
lra-assigns.c:1363