Stop backends from needing to support nullary intrinsics

[oli-obk]

And then remove our infrastructure special casing them. Further improvements can now be done to them by avoiding the intermediate ConstValue step, but let's leave that to follow up work

r? @RalfJung

[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

Some changes occurred to the CTFE / Miri interpreter

cc @rust-lang/miri

Some changes occurred in compiler/rustc_codegen_cranelift

cc @bjorn3

Some changes occurred to the CTFE machinery

cc @RalfJung, @oli-obk, @lcnr

Some changes occurred in compiler/rustc_codegen_ssa

cc @WaffleLapkin

[oli-obk]

@bors try @rust-timer queue

[bors]

⌛ Trying commit a44843e with merge a5e9784...

[fbstj]

nit: I see this is a code-move & fixup to work in here, but is it worth sorting these arms into the rest of the match? though I guess the other arms are also not sorted simply... it was mostly that needs_drop is between type_id & type_name that caught my eye hehe

[oli-obk]

yea, could do that, good point. didn't want to do it in the first commit to kinda make the diff line up

[bors]

☀️ Try build successful - checks-actions
Build commit: a5e9784 (a5e97845d0268f3cbfc1f7da350c0e9127ab0b99)

[rust-timer]

Finished benchmarking commit (a5e9784): comparison URL.

Overall result: ❌✅ regressions and improvements - please read the text below

Benchmarking this pull request means it may be perf-sensitive – we'll automatically label it not fit for rolling up. You can override this, but we strongly advise not to, due to possible changes in compiler perf.

Next Steps: If you can justify the regressions found in this try perf run, please do so in sufficient writing along with @rustbot label: +perf-regression-triaged. If not, please fix the regressions and do another perf run. If its results are neutral or positive, the label will be automatically removed.

@bors rollup=never
@rustbot label: -S-waiting-on-perf +perf-regression

Instruction count

Our most reliable metric. Used to determine the overall result above. However, even this metric can be noisy.

	mean	range	count
Regressions ❌ (primary)	3.2%	[2.8%, 3.5%]	2
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.3%	[-0.3%, -0.3%]	1
Improvements ✅ (secondary)	-0.3%	[-0.3%, -0.2%]	2
All ❌✅ (primary)	2.0%	[-0.3%, 3.5%]	3

Max RSS (memory usage)

Results (primary 3.7%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	3.7%	[2.0%, 5.5%]	2
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	3.7%	[2.0%, 5.5%]	2

Cycles

Results (primary 2.7%, secondary -6.5%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	2.7%	[2.7%, 2.8%]	2
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-6.5%	[-6.5%, -6.5%]	1
All ❌✅ (primary)	2.7%	[2.7%, 2.8%]	2

Binary size

Results (primary 0.4%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	0.5%	[0.0%, 1.1%]	9
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.1%	[-0.1%, -0.0%]	2
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.4%	[-0.1%, 1.1%]	11

Bootstrap: 691.091s -> 687.91s (-0.46%)
Artifact size: 371.86 MiB -> 371.89 MiB (0.01%)

[rustbot]

Some changes occurred in compiler/rustc_codegen_gcc

cc @antoyo, @GuillaumeGomez

[rust-log-analyzer]

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

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

tests/pass/shims/x86/intrinsics-x86-avx2.rs ... ok
tests/pass/shims/x86/intrinsics-x86-gfni.rs ... ok

FAILED TEST: tests/pass/float.rs
command: MIRI_ENV_VAR_TEST="0" MIRI_TEMP="/tmp/miri-uitest-HxvQaw" RUST_BACKTRACE="1" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/bin/miri" "--error-format=json" "--sysroot=/checkout/obj/build/x86_64-unknown-linux-gnu/miri-sysroot" "-Dwarnings" "-Dunused" "-Ainternal_features" "-Zui-testing" "--out-dir" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage1-tools/x86_64-unknown-linux-gnu/tmp/miri_ui/0/tests/pass" "tests/pass/float.rs" "--edition" "2021" "--target" "i686-pc-windows-msvc"

error: test got exit status: 101, but expected 0
 = note: the compiler panicked

error: no output was expected
Execute `./miri test --bless` to update `tests/pass/float.stderr` to the actual output
+++ <stderr output>

thread 'main' panicked at tests/pass/float.rs:1378:5:
expected non-determinism, got 16 times the same result: true
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
note: in Miri, you may have to set `MIRIFLAGS=-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect


full stderr:

thread 'main' panicked at tests/pass/float.rs:1378:5:
expected non-determinism, got 16 times the same result: true
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
note: in Miri, you may have to set `MIRIFLAGS=-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect

full stdout:


FAILURES:
---

Location:
   /cargo/registry/src/index.crates.io-1949cf8c6b5b557f/ui_test-0.29.2/src/lib.rs:369

Backtrace omitted. Run with RUST_BACKTRACE=1 environment variable to display it.
Run with RUST_BACKTRACE=full to include source snippets.
error: test failed, to rerun pass `--test ui`

Caused by:
  process didn't exit successfully: `/checkout/obj/build/x86_64-unknown-linux-gnu/stage1-tools/x86_64-unknown-linux-gnu/release/deps/ui-40dd690eb6b2c4a4` (exit status: 1)
Command has failed. Rerun with -v to see more details.
Build completed unsuccessfully in 0:01:57
  local time: Wed Jun 25 09:11:50 UTC 2025
  network time: Wed, 25 Jun 2025 09:11:50 GMT
##[error]Process completed with exit code 1.
Post job cleanup.

[oli-obk]

oops wrong PR

r? @RalfJung