If a register is used for both input and output by a SAME_INPUT_OUTPUT
operand, then it represents a different virtual register for the end
use-position of an instruction (since that will become the output's
virtual register). It therefore can't be used to represent the input
virtual register for any input operands that are USED_AT_END.

BUG=chromium:1163715,v8:9684

Change-Id: I8dc0008ba81d5f1d0e38091b6dc013725c62b1b4
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2632700Reviewed-by: Santiago Aboy Solanes <solanes@chromium.org>
Commit-Queue: Ross McIlroy <rmcilroy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#72149}