Target: Add mips mti baremetal support

[wzssyqa]

Do the same thing as gcc, which use the vendor mti to mark the toolchain as MIPS32r2 default.

We support both big endian and little endian flavor:
mips-mti-none-elf
mipsel-mti-none-elf

[rustbot]

r? @oli-obk

rustbot has assigned @oli-obk.
They will have a look at your PR within the next two weeks and either review your PR or reassign to another reviewer.

Use r? to explicitly pick a reviewer

[rustbot]

These commits modify compiler targets.
(See the Target Tier Policy.)

Some changes occurred in src/doc/rustc/src/platform-support

cc @Noratrieb

[wzssyqa]

I noticed #134721.
For baremetal toolchain, we may follow the gcc naming.

[oli-obk]

Who is maintaining the mips targets?

[wzssyqa]

Who is maintaining the mips targets?

It's me. I am also the MIPS maintainer of GCC/LLVM mips maintainer.

[oli-obk]

how is the new mipsel target different from mipsel-unknown-none and should the none target keep existing at all?

[wzssyqa]

how is the new mipsel target different from mipsel-unknown-none and should the none target keep existing at all?

Maybe we should remove unknown target or switch it to mips2 instead of mips32r2.
For the triple policy of MIPS in gcc, the default vendor (unknown) means mips1 (for 32bit) or mips3 (for 64bit).

We use the vendor mti for toolchains for MIPSr2, and img for MIPSr6.

If there is no objection, I will switch mipsel-unknown-none to mips2, due to LLVM has no mips1 support yet.

[wzssyqa]

For -mti- toolchains we try to use lld instead of gnu ld, which is another difference.

[oli-obk]

@bors r+ rollup

Let's land this and look at the unknown target(s?) In follow-ups. If they have no users we should probably just remove them instead of doing sth that no one is testing that it works

[bors]

📌 Commit 1a82287 has been approved by oli-obk

It is now in the queue for this repository.

[bors]

⌛ Testing commit 1a82287 with merge 7270e73...

[bors]

☀️ Test successful - checks-actions
Approved by: oli-obk
Pushing 7270e73 to master...

[rust-timer]

Finished benchmarking commit (7270e73): comparison URL.

Overall result: ❌✅ regressions and improvements - no action needed

@rustbot label: -perf-regression

Instruction count

This is the most reliable metric that we have; it was used to determine the overall result at the top of this comment. However, even this metric can sometimes exhibit noise.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	0.4%	[0.4%, 0.5%]	3
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-0.2%	[-0.2%, -0.2%]	1
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

Results (primary -3.2%, secondary -1.7%)

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-3.2%	[-3.2%, -3.2%]	1
Improvements ✅ (secondary)	-1.7%	[-2.2%, -1.4%]	5
All ❌✅ (primary)	-3.2%	[-3.2%, -3.2%]	1

Cycles

Results (primary -2.3%)

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-2.3%	[-2.3%, -2.3%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-2.3%	[-2.3%, -2.3%]	1

Binary size

This benchmark run did not return any relevant results for this metric.

Bootstrap: 763.624s -> 763.064s (-0.07%)
Artifact size: 325.63 MiB -> 325.65 MiB (0.01%)