Allow `enum` and `union` literals to also create SSA values #138759

scottmcm · 2025-03-20T18:41:17Z

Today, Some(x) always goes through an alloca, even in trivial cases where the niching means the constructor doesn't even change the value.

For example, https://rust.godbolt.org/z/6KG6PqoYz

pub fn demo(r: &i32) -> Option<&i32> {
    Some(r)
}

currently emits the IR

define align 4 ptr @demo(ptr align 4 %r) unnamed_addr {
start:
  %_0 = alloca [8 x i8], align 8
  store ptr %r, ptr %_0, align 8
  %0 = load ptr, ptr %_0, align 8
  ret ptr %0
}

but with this PR it becomes just

define align 4 ptr @demo(ptr align 4 %r) unnamed_addr {
start:
  ret ptr %r
}

(Of course the optimizer can clean that up, but it'd be nice if it didn't have to -- especially in debug where it doesn't run. This is like #123886, but that only handled non-simd structs -- this PR generalizes it to all non-simd ADTs.)

Doing this means handing variants other than FIRST_VARIANT, handling the active field for unions, refactoring the discriminant code so the Place and Operand parts can share the calculation, etc.

Other PRs that led up to this one:

try-job: aarch64-gnu

rustbot · 2025-03-20T18:41:22Z

r? @Nadrieril

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rustbot · 2025-03-20T18:41:24Z

Some changes occurred in compiler/rustc_codegen_ssa

cc @WaffleLapkin

rustbot · 2025-03-20T18:58:00Z

These commits modify the Cargo.lock file. Unintentional changes to Cargo.lock can be introduced when switching branches and rebasing PRs.

If this was unintentional then you should revert the changes before this PR is merged.
Otherwise, you can ignore this comment.

saethlin · 2025-03-20T20:14:02Z

r? codegen

saethlin · 2025-03-20T20:14:16Z

Spiderman meme

scottmcm · 2025-03-20T20:22:43Z

@bors try @rust-timer queue

bors · 2025-03-20T20:23:55Z

⌛ Trying commit aa8ceb8 with merge 875f416...

Allow `enum` and `union` literals to also create SSA values Today, `Some(x)` always goes through an `alloca`, even in trivial cases where the niching means the constructor doesn't even change the value. For example, <https://rust.godbolt.org/z/6KG6PqoYz> ```rust pub fn demo(r: &i32) -> Option<&i32> { Some(r) } ``` currently emits the IR ```llvm define align 4 ptr `@demo(ptr` align 4 %r) unnamed_addr { start: %_0 = alloca [8 x i8], align 8 store ptr %r, ptr %_0, align 8 %0 = load ptr, ptr %_0, align 8 ret ptr %0 } ``` but with this PR it becomes just ```llvm define align 4 ptr `@demo(ptr` align 4 %r) unnamed_addr { start: ret ptr %r } ``` (Of course the optimizer can clean that up, but it'd be nice if it didn't have to -- especially in debug where it doesn't run. This is like rust-lang#123886, but that only handled non-simd `struct`s -- this PR generalizes it to all non-simd ADTs.) There's two commits you can review independently: 1. The first is simplifying how the aggregate handling works. Past-me wrote something overly complicated, needing arrayvecs and zipping, depending on a careful iteration order of the fields, and fragile enough that even for just structs it needed extra double-checks to make sure it even made the right variant. It's replaced with something far more direct that works just like `extract_field`: use the offset to put it in exactly the correct immediate in the `OperandValue`. This doesn't support anything new, just refactors -- including moving some things off `FunctionCx` that had no reason to be there. (I have no idea why my past self put them there.) 2. The second extends that work to support more ADTs. That means handing variants other than `FIRST_VARIANT`, handling the active field for unions, refactoring the discriminant code so the Place and Operand parts can share the calculation, etc.

bors · 2025-03-20T22:32:13Z

☀️ Try build successful - checks-actions
Build commit: 875f416 (875f416b9aa583f09153eac5b56d36fcd932b274)

rust-timer · 2025-03-20T23:49:26Z

Finished benchmarking commit (875f416): comparison URL.

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

Benchmarking this pull request likely means that it is perf-sensitive, so we're automatically marking it as not fit for rolling up. While you can manually mark this PR as fit for rollup, we strongly recommend not doing so since this PR may lead to changes in compiler perf.

Next Steps: If you can justify the regressions found in this try perf run, please indicate this with @rustbot label: +perf-regression-triaged along with sufficient written justification. If you cannot justify the regressions please fix the regressions and do another perf run. If the next run shows neutral or positive results, the label will be automatically removed.

@bors rollup=never
@rustbot label: -S-waiting-on-perf +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)	0.0%	[0.0%, 0.0%]	1
Regressions ❌ (secondary)	0.2%	[0.2%, 0.3%]	3
Improvements ✅ (primary)	-0.3%	[-0.5%, -0.2%]	7
Improvements ✅ (secondary)	-0.3%	[-0.4%, -0.3%]	2
All ❌✅ (primary)	-0.3%	[-0.5%, 0.0%]	8

Max RSS (memory usage)

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

Cycles

Results (secondary -2.1%)

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)	-	-	0
Improvements ✅ (secondary)	-2.1%	[-2.3%, -1.6%]	8
All ❌✅ (primary)	-	-	0

Binary size

Results (primary -0.1%, secondary -0.1%)

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)	-0.1%	[-0.2%, -0.0%]	57
Improvements ✅ (secondary)	-0.1%	[-0.3%, -0.0%]	27
All ❌✅ (primary)	-0.1%	[-0.2%, -0.0%]	57

Bootstrap: 775.297s -> 774.424s (-0.11%)
Artifact size: 365.52 MiB -> 365.52 MiB (0.00%)

rustbot · 2025-03-23T04:48:35Z

Some changes occurred to the CTFE machinery

cc @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

scottmcm · 2025-03-28T21:49:10Z

Ben said I should re-roll this
r? codegen

workingjubilee · 2025-05-01T04:52:21Z

hello.

Let `rvalue_creates_operand` return true for *all* `Rvalue::Aggregate`s Draft for now because it's built on Ralf's #143291 Inspired by #138759 (comment) where I noticed that we were nearly at this point, plus the comments I was writing in #143410 that reminded me a type-dependent `true` is fine. This PR splits the `OperandRef::builder` logic out to a separate type, with the updates needed to handle SIMD as well. In doing so, that makes the existing `Aggregate` path in `codegen_rvalue_operand` capable of handing SIMD values just fine. As a result, we no longer need to do layout calculations for aggregate result types when running the analysis to determine which things can be SSA in codegen.

Inspired by <rust-lang#138759 (comment)> where I noticed that we were nearly at this point, plus the comments I was writing in 143410 that reminded me a type-dependent `true` is fine. This PR splits the `OperandRef::builder` logic out to a separate type, with the updates needed to handle SIMD as well. In doing so, that makes the existing `Aggregate` path in `codegen_rvalue_operand` capable of handing SIMD values just fine. As a result, we no longer need to do layout calculations for aggregate result types when running the analysis to determine which things can be SSA in codegen.

Let `rvalue_creates_operand` return true for *all* `Rvalue::Aggregate`s ~~Draft for now because it's built on Ralf's #143291~~ Inspired by #138759 (comment) where I noticed that we were nearly at this point, plus the comments I was writing in #143410 that reminded me a type-dependent `true` is fine. This PR splits the `OperandRef::builder` logic out to a separate type, with the updates needed to handle SIMD as well. In doing so, that makes the existing `Aggregate` path in `codegen_rvalue_operand` capable of handing SIMD values just fine. As a result, we no longer need to do layout calculations for aggregate result types when running the analysis to determine which things can be SSA in codegen.

Let `rvalue_creates_operand` return true for *all* `Rvalue::Aggregate`s ~~Draft for now because it's built on Ralf's rust-lang/rust#143291~~ Inspired by rust-lang/rust#138759 (comment) where I noticed that we were nearly at this point, plus the comments I was writing in rust-lang/rust#143410 that reminded me a type-dependent `true` is fine. This PR splits the `OperandRef::builder` logic out to a separate type, with the updates needed to handle SIMD as well. In doing so, that makes the existing `Aggregate` path in `codegen_rvalue_operand` capable of handing SIMD values just fine. As a result, we no longer need to do layout calculations for aggregate result types when running the analysis to determine which things can be SSA in codegen.

Inspired by <rust-lang#138759 (comment)> where I noticed that we were nearly at this point, plus the comments I was writing in 143410 that reminded me a type-dependent `true` is fine. This PR splits the `OperandRef::builder` logic out to a separate type, with the updates needed to handle SIMD as well. In doing so, that makes the existing `Aggregate` path in `codegen_rvalue_operand` capable of handing SIMD values just fine. As a result, we no longer need to do layout calculations for aggregate result types when running the analysis to determine which things can be SSA in codegen.

Let `rvalue_creates_operand` return true for *all* `Rvalue::Aggregate`s ~~Draft for now because it's built on Ralf's rust-lang/rust#143291~~ Inspired by rust-lang/rust#138759 (comment) where I noticed that we were nearly at this point, plus the comments I was writing in rust-lang/rust#143410 that reminded me a type-dependent `true` is fine. This PR splits the `OperandRef::builder` logic out to a separate type, with the updates needed to handle SIMD as well. In doing so, that makes the existing `Aggregate` path in `codegen_rvalue_operand` capable of handing SIMD values just fine. As a result, we no longer need to do layout calculations for aggregate result types when running the analysis to determine which things can be SSA in codegen.

Inspired by <rust-lang#138759 (comment)> where I noticed that we were nearly at this point, plus the comments I was writing in 143410 that reminded me a type-dependent `true` is fine. This PR splits the `OperandRef::builder` logic out to a separate type, with the updates needed to handle SIMD as well. In doing so, that makes the existing `Aggregate` path in `codegen_rvalue_operand` capable of handing SIMD values just fine. As a result, we no longer need to do layout calculations for aggregate result types when running the analysis to determine which things can be SSA in codegen.

saethlin · 2025-10-09T22:42:31Z

@craterbot run mode=build-and-test start=master#d98a5da813da67eb189387b8ccfb73cf481275d8+rustflags=-Copt-level=3 end=master#733b47ea4b1b86216f14ef56e49440c33933f230+rustflags=-Copt-level=3

craterbot · 2025-10-09T22:42:48Z

👌 Experiment pr-138759 created and queued.
🔍 You can check out the queue and this experiment's details.

ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

craterbot · 2025-10-11T04:02:39Z

🚧 Experiment pr-138759 is now running

ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

…ottmcm Change int-to-ptr transmute lowering back to inttoptr This is a revert of rust-lang#121282, but with a regression test to cover the reported miscompile in rust-lang#147265 that was caused by the way the code here combines with rust-lang#138759.

Change int-to-ptr transmute lowering back to inttoptr This is a revert of #121282, but with a regression test to cover the reported miscompile in #147265 that was caused by the way the code here combines with #138759.

Change int-to-ptr transmute lowering back to inttoptr This is a revert of rust-lang/rust#121282, but with a regression test to cover the reported miscompile in rust-lang/rust#147265 that was caused by the way the code here combines with rust-lang/rust#138759.

craterbot · 2025-10-15T12:29:07Z

🎉 Experiment pr-138759 is completed!
📊 272 regressed and 231 fixed (713837 total)
📊 6273 spurious results on the retry-regessed-list.txt, consider a retry¹ if this is a significant amount.
📰 Open the summary report.

⚠️ If you notice any spurious failure please add them to the denylist!
ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

re-run the experiment with crates=https://crater-reports.s3.amazonaws.com/pr-138759/retry-regressed-list.txt ↩

saethlin · 2025-10-15T12:35:32Z

@craterbot run mode=build-and-test start=master#d98a5da813da67eb189387b8ccfb73cf481275d8+rustflags=-Copt-level=3 end=master#733b47ea4b1b86216f14ef56e49440c33933f230+rustflags=-Copt-level=3 crates=https://crater-reports.s3.amazonaws.com/pr-138759/retry-regressed-list.txt name=pr-138759-retry p=1

craterbot · 2025-10-15T12:35:43Z

👌 Experiment pr-138759-retry created and queued.
🔍 You can check out the queue and this experiment's details.

ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

rustbot assigned Nadrieril Mar 20, 2025

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scottmcm force-pushed the operand-builder branch from 9423566 to a9031aa Compare March 23, 2025 05:04

scottmcm mentioned this pull request Mar 23, 2025

Simplify PartialOrd on tuples containing primitives #138135

Merged

rustbot assigned workingjubilee and unassigned saethlin Mar 28, 2025

scottmcm mentioned this pull request Apr 1, 2025

Rust fails to optimize away useless unwrap check #57166

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scottmcm mentioned this pull request Jul 5, 2025

Let rvalue_creates_operand return true for *all* Rvalue::Aggregates #143502

Merged

hanna-kruppe mentioned this pull request Aug 2, 2025

Large match statements that compile down to small assembly don't get inlined automatically #118921

Open

nnethercote mentioned this pull request Oct 1, 2025

Update to nightly-2025-07-07. Rust-GPU/rust-gpu#420

Open

apiraino mentioned this pull request Oct 6, 2025

Rust 1.90 compiler optimization (O2, O3) triggers UB with Box::from_raw() #147265

Open

craterbot added S-waiting-on-crater Status: Waiting on a crater run to be completed. and removed S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. labels Oct 9, 2025

saethlin mentioned this pull request Oct 9, 2025

Change int-to-ptr transmute lowering back to inttoptr #147541

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craterbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-crater Status: Waiting on a crater run to be completed. labels Oct 15, 2025

craterbot added S-waiting-on-crater Status: Waiting on a crater run to be completed. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Oct 15, 2025

Allow enum and union literals to also create SSA values #138759

Allow enum and union literals to also create SSA values #138759

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

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Max RSS (memory usage)

Cycles

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Allow `enum` and `union` literals to also create SSA values #138759

Allow `enum` and `union` literals to also create SSA values #138759

scottmcm commented Mar 20, 2025 •

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