Fix alignment of stores to scalar pair

[nikic]

The alignment for the second element of a scalar pair is not the same as for the first element, make sure it is calculated correctly. This fixes #56267.

r? @eddyb

[eddyb]

@nikomatsakis @Mark-Simulacrum Any chance we could still get this into the beta?

[eddyb]

@bors r+

[bors]

📌 Commit d8190af has been approved by eddyb

[Mark-Simulacrum]

Cc @rust-lang/compiler for beta approval. This fixes a clear beta regression but I'm not sure what the impact of that regression is.

Overall I'm fairly neutral on backporting - the patch looks relatively small.

[oli-obk]

Accepting for beta, small patch for fixing an unsoundness regression.

[emilyalbini]

@bors p=10 (beta-accepted)

[eddyb]

I think there's more, similar, issues, I tried to do a search and found this:

rust/src/librustc_codegen_llvm/builder.rs

Line 594 in b68fc18

let load = self.load(llptr, place.align);

That's the load counterpart to this PR, so I think it should also be fixed..

EDIT: I'll be opening a PR soon.
EDIT2: Here it is: #56329.

[eddyb]

This could be using %{{.+}}, since TMP1 and TMP2 aren't used. (but we should merge this PR first)

[bors]

⌛ Testing commit d8190af with merge 5f387a6...

[bors]

☀️ Test successful - status-appveyor, status-travis
Approved by: eddyb
Pushing 5f387a6 to master...

[nikomatsakis]

Removing beta-accepted so we can discuss in today's @rust-lang/compiler meeting.

[nikomatsakis]

Relevant: affects num-cpus, a pretty fundamental crate

[pnkfelix]

discussed in T-compiler meeting. beta-accepting.

[alexcrichton]

@nikic can you help out with the backport to beta? While this patch applies cleanly it generates:

error[E0277]: the trait bound `&builder::Builder<'_, 'll, 'tcx>: rustc_target::abi::HasDataLayout` is not satisfied
   --> librustc_codegen_llvm/mir/operand.rs:301:47
    |
301 |                 let b_offset = a_scalar.value.size(bx).align_to(b_scalar.value.align(bx).abi);
    |                                               ^^^^ the trait `rustc_target::abi::HasDataLayout` is not implemented for `&builder::Builder<'_, 'll, 'tcx>`

error[E0599]: no method named `align_to` found for type `rustc_target::abi::Size` in the current scope
   --> librustc_codegen_llvm/mir/operand.rs:301:56
    |
301 |                 let b_offset = a_scalar.value.size(bx).align_to(b_scalar.value.align(bx).abi);
    |                                                        ^^^^^^^^

error[E0277]: the trait bound `&builder::Builder<'_, 'll, 'tcx>: rustc_target::abi::HasDataLayout` is not satisfied
   --> librustc_codegen_llvm/mir/operand.rs:301:80
    |
301 |                 let b_offset = a_scalar.value.size(bx).align_to(b_scalar.value.align(bx).abi);
    |                                                                                ^^^^^ the trait `rustc_target::abi::HasDataLayout` is not implemented for `&builder::Builder<'_, 'll, 'tcx>`

error[E0615]: attempted to take value of method `abi` on type `rustc_target::abi::Align`
   --> librustc_codegen_llvm/mir/operand.rs:301:90
    |
301 |                 let b_offset = a_scalar.value.size(bx).align_to(b_scalar.value.align(bx).abi);
    |                                                                                          ^^^
    |
    = help: maybe a `()` to call it is missing?

error: aborting due to 4 previous errors

Some errors occurred: E0277, E0599, E0615.
For more information about an error, try `rustc --explain E0277`.

and I'm not sure how to easily fix those off the top of my head!

[nikic]

@alexcrichton The bx arguments probably need to be bx.cx on beta.

[nikic]

The whole expression should be a_scalar.value.size(bx.cx).abi_align(b_scalar.value.align(bx.cx)).

[alexcrichton]

Thanks! I think that solves the first and third errors, but the second/fourth still persist :(

error[E0599]: no method named `align_to` found for type `rustc_target::abi::Size` in the current scope
   --> librustc_codegen_llvm/mir/operand.rs:301:59
    |
301 |                 let b_offset = a_scalar.value.size(bx.cx).align_to(b_scalar.value.align(bx.cx).abi);
    |                                                           ^^^^^^^^

error[E0615]: attempted to take value of method `abi` on type `rustc_target::abi::Align`
   --> librustc_codegen_llvm/mir/operand.rs:301:96
    |
301 |                 let b_offset = a_scalar.value.size(bx.cx).align_to(b_scalar.value.align(bx.cx).abi);
    |                                                                                                ^^^
    |
    = help: maybe a `()` to call it is missing?

error: aborting due to 2 previous errors

Some errors occurred: E0599, E0615.
For more information about an error, try `rustc --explain E0599`.

[nikic]

@alexcrichton Could you please try the a_scalar.value.size(bx.cx).abi_align(b_scalar.value.align(bx.cx)) variant from my last comment? That's what similar code on beta uses. If that doesn't do it I'll try locally.

[alexcrichton]

Appears to work! Or at least it compiles, running some tests real quick. Thanks!