... in order to improve quality of C++ assembly.

This CL also switches C++ code to use branchful decompression.

Bug: v8:9353
Change-Id: Id6a5cc5db2ad729b4394cd541a7ec8035c0d4571
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1677204
Commit-Queue: Igor Sheludko <ishell@chromium.org>
Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/master@{#62372}

Bug: v8:9247
Change-Id: I2f999ed3a8cc0931e5092f2ac6e709b8ff3f9e42
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1630678
Commit-Queue: Yang Guo <yangguo@chromium.org>
Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#61896}

TBR=mvstanton@chromium.org,neis@chromium.org,ahaas@chromium.org

Bug: v8:9247
Change-Id: I5433c863a54f3412d73df0d38aba3fdbcfac7ebe
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1627973
Commit-Queue: Yang Guo <yangguo@chromium.org>
Auto-Submit: Yang Guo <yangguo@chromium.org>
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#61830}

This CL uses pc-relative jumps and calls (B/BL) for calls from embedded
builtins to embedded builtins. To make this work, the code range size is
limited to 32MB on arm during mksnapshot, which ensures that all builtin
to builtin offsets for jumps/calls fit into the B/BL immediate. At code
generation time, we put a placeholder into the instruction offset which
we resolve to the right code object when the code is copied to the heap.
We use a new relocation mode RELATIVE_CODE_TARGET for these relative jumps.
The relocation mode RELATIVE_CODE_TARGET should never appear after
generating the snapshot.

We modify the target_address/set_target_address methods of RelocInfo
such that they return the absolute target addresses for pc-relative B/BL
instructions. This ensures that the GC can treat RELATIVE_CODE_TARGET in
the same way as code targets. This, however, only matters during
snapshot creation time, and production code never contains
RELATIVE_CODE_TARGET relocations.

Bug: v8:6666
Cq-Include-Trybots: luci.chromium.try:linux_chromium_rel_ng
Change-Id: If7eab83ad588859ca87c654a5ddc3e37caea884c
Reviewed-on: https://chromium-review.googlesource.com/1117181Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Commit-Queue: Sigurd Schneider <sigurds@chromium.org>
Cr-Commit-Position: refs/heads/master@{#54320}

We had a kRootRegisterBias on x64 before. This CL ports the feature to
all other platforms as well. The root register bias is helpful to adjust
the value of the root register, which allows to better utilize signed
immediate offset constants in load instructions.

We currently use a separate add instruction to add kRootRegisterBias
in the code that initializes the root register. This could be improved
by adding a custom relocation mode ensuring that instead of the root
address, the root address plus the bias is inserted (and in this way
the add instruction can be omitted).

Bug: v8:6666
Change-Id: I55cf02ab85d11e3c6d0d83a8f7905dbf924890f1
Reviewed-on: https://chromium-review.googlesource.com/1113539
Commit-Queue: Sigurd Schneider <sigurds@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#54023}