Add -Z small-data-threshold

[paulmenage]

Proposal

On some targets (including MIPS, M68K, RISC-V, Hexagon) and configurations, LLVM will place small static data objects in the .sdata and .sbss sections, intended to allow size optimizations in embedded systems that can access data in these sections via small offsets from a register. LLVM provides command line arguments and/or IR module flags to control/disable this behavior in the event that it's unwanted, but they're different on every target.

This proposal is to add the -Z small-data-threshold flag, which appropriately configures LLVM's small-data threshold for the target in use.

See rust-lang/rust#117465 for a possible implementation of the proposed change.

Mentors or Reviewers

Process

The main points of the Major Change Process are as follows:

• File an issue describing the proposal.
• A compiler team member or contributor who is knowledgeable in the area can second by writing @rustbot second.
  • Finding a "second" suffices for internal changes. If however, you are proposing a new public-facing feature, such as a -C flag, then full team check-off is required.
  • Compiler team members can initiate a check-off via @rfcbot fcp merge on either the MCP or the PR.
• Once an MCP is seconded, the Final Comment Period begins. If no objections are raised after 10 days, the MCP is considered approved.

You can read more about Major Change Proposals on forge.

Comments

[rustbot]

This issue is not meant to be used for technical discussion. There is a Zulip stream for that. Use this issue to leave procedural comments, such as volunteering to review, indicating that you second the proposal (or third, etc), or raising a concern that you would like to be addressed.

cc @rust-lang/compiler @rust-lang/compiler-contributors

[nikic]

@rustbot second

[apiraino]

@rustbot label -final-comment-period +major-change-accepted