Hydrogen attempts to force representation changes on certain operations in order
to deoptimise on the change rather than the operation. However, these forced
changes are often unnecessary on 64-bit platforms, and cause poor code
generation, so this patch makes some of them conditional on whether it's
possible for deoptimisation to occur in the change.
On ARM64, this prevents sequences like:
;;; <@46,#89> smi-tag
0x7ff282c7f050 144 lsl x4, x4, #32
;;; <@48,#90> smi-untag
0x7ff282c7f054 148 asr x5, x4, #32
;;; <@50,#31> mul-const-i-s
0x7ff282c7f058 152 lsl w6, w5, #3
BUG=
R=jkummerow@chromium.org
Review URL: https://codereview.chromium.org/303263010
git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21818 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
649057e05c