[Bug rtl-optimization/87871] [9 Regression] testcases fail after r265398 on arm

[bergner at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87871

--- Comment #28 from Peter Bergner <bergner at gcc dot gnu.org> ---
Vlad, in looking at add_insn_allocno_copies(), it looks like it relies on
seeing REG_DEAD notes on whether to record a copy/shuffle that should be
handled.  Shouldn't we instead be looking at whether the source and destination
regs conflict or not?  Ie, there might not be a REG_DEAD note, but that doesn't
mean the two regs/pseudos conflict.  And conversely, if there is a REG_DEAD
note on the copy/shuffle, the two regs/pseudos still could conflict.