[Bug target/63442] [AArch64] ICE with ubsan/overflow-int128.c test

[jiwang at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63442

--- Comment #4 from Jiong Wang <jiwang at gcc dot gnu.org> ---
the root cause should be one minor bug in prepare_cmp_insn.

the last mode parameter "pmode" of "prepare_cmp_insn" should match the mode of
the first parameter "x", while during the recursive call of "prepare_cmp_insn",

x is with mode of targetm.libgcc_cmp_return_mode (),
pmode is assign to word_mode.

there comes the problem, aarch64 implemented libgcc_cmp_return_mode to always
return SImode, so there is a unmatch.

we should assign pmode with targetm.libgcc_cmp_return_mode () also.

this problem is hidding because nearly all other targets use the default hook
which return word_mode.