Cleanup offload datatransfer

[ZuseZ4]

There are 3 steps to run code on a GPU: Copy data from the host to the device, launch the kernel, and move it back.
At the moment, we have a single variable describing the memory handling to do in each step, but that makes it hard for LLVM's opt pass to understand what's going on. We therefore split it into three variables, each only including the bits relevant for the corresponding stage.

cc @jdoerfert @kevinsala

r? compiler

[ZuseZ4]

I don't think jieyouxu will want to review this part of rustc.
r? @oli-obk

[rustbot]

oli-obk is not on the review rotation at the moment.
They may take a while to respond.

[rustbot]

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

[ZuseZ4]

@rustbot reroll

[rustbot]

Some changes occurred to the intrinsics. Make sure the CTFE / Miri interpreter
gets adapted for the changes, if necessary.

cc @rust-lang/miri, @RalfJung, @oli-obk, @lcnr

[rust-log-analyzer]

The job x86_64-gnu-tools failed! Check out the build log: (web) (plain enhanced) (plain)

Click to see the possible cause of the failure (guessed by this bot)

REPOSITORY                                   TAG       IMAGE ID       CREATED      SIZE
ghcr.io/dependabot/dependabot-updater-core   latest    bcec0b4e062b   6 days ago   783MB
=> Removing docker images...
Deleted Images:
untagged: ghcr.io/dependabot/dependabot-updater-core:latest
untagged: ghcr.io/dependabot/dependabot-updater-core@sha256:b662be51f7b8ef7e2c8464428f14e49cb79c36aa9afb7ecb9221dfe0f507050c
deleted: sha256:bcec0b4e062b5ffe11cc1c2729558c0cd96621c0271ab5e97ff3a56e0c25045a
deleted: sha256:64e147d5e54d9be8b8aa322e511cda02296eda4b8b8d063c6a314833aca50e29
deleted: sha256:5cba409bb463f4e7fa1a19f695450170422582c1bc7c0e934d893b4e5f558bc6
deleted: sha256:cddc6ebd344b0111eaab170ead1dfda24acdfe865ed8a12599a34d338fa8e28b
deleted: sha256:2412c3f334d79134573cd45e657fb6cc0abd75bef3881458b0d498d936545c8d
---
tests/ui/double_parens.rs ... ok
tests/ui/duplicate_underscore_argument.rs ... ok
tests/ui/drop_non_drop.rs ... ok
tests/ui/duplicated_attributes.rs ... ok
tests/ui/duration_suboptimal_units_days_weeks.rs ... ok
tests/ui/duration_suboptimal_units.rs ... ok
tests/ui/duration_suboptimal_units_days_weeks.fixed ... ok
tests/ui/duration_subsec.rs ... ok
tests/ui/double_parens.fixed ... ok
tests/ui/duration_suboptimal_units.fixed ... ok
tests/ui/duration_subsec.fixed ... ok
tests/ui/eager_transmute.rs ... ok
---
...............................................    (147/147)

======== tests/rustdoc-gui/globals.goml ========

[ERROR] line 14: Error: The window properties still all match: for command `wait-for-window-property-false: {"searchIndex": null}`
    at <file:///checkout/obj/build/x86_64-unknown-linux-gnu/test/rustdoc-gui/doc/test_docs/index.html?search=Foo>

======== tests/rustdoc-gui/search-result-display.goml ========

[WARNING] line 39: Delta is 0 for "x", maybe try to use `compare-elements-position` instead?

[ZuseZ4]

spurious failure, cc @jieyouxu
I think the doc ones fail somewhat often, lately? But I couldn't find this one in the open issues.