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Fixup if T::CONST in MIR #123259

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Fixup if T::CONST in MIR #123259

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scottmcm
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r? ghost

@rustbot rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Mar 31, 2024
scottmcm
scottmcm commented Mar 31, 2024
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tests/mir-opt/pre-codegen/slice_iter.forward_loop.PreCodegen.after.panic-abort.mir
@@ -25,19 +25,18 @@ fn forward_loop(_1: &[T], _2: impl Fn(&T)) -> () {
debug slice => _1;
let _3: usize;
let mut _5: std::ptr::NonNull<[T]>;
let mut _8: bool;
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This PR means this local -- and its associated storage markers -- are no longer needed.

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@bors try @rust-timer queue

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@rustbot rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Mar 31, 2024
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bors commented Mar 31, 2024

⌛ Trying commit 2fb9d27 with merge 3d3fbc3...

bors added a commit to rust-lang-ci/rust that referenced this pull request Mar 31, 2024
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Auto merge of rust-lang#123259 - scottmcm:tweak-if-const, r=<try>
3d3fbc3 
Fixup `if T::CONST` in MIR

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RalfJung
RalfJung reviewed Mar 31, 2024
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compiler/rustc_mir_transform/src/switch_const.rs

/// A `MirPass` for simplifying `if T::CONST`.
///
/// Today, MIR building for things like `if T::IS_ZST` introduce a constant
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Suggested change
/// Today, MIR building for things like `if T::IS_ZST` introduce a constant
/// Today, MIR building for things like `if T::IS_ZST` introduce a temporary

RalfJung
RalfJung reviewed Mar 31, 2024
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compiler/rustc_mir_transform/src/switch_const.rs
#[derive(Default)]
pub struct SwitchConst;

impl<'tcx> MirPass<'tcx> for SwitchConst {
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Note that as a pass that runs in opt-level 0, this pass should not do UB-based reasoning or transform code with UB into code without UB. Miri relies on that.

The pass seems fine but this is worth pointing out with a comment as the requirement is implicit in the absence of an opt-level check.

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bors commented Mar 31, 2024

☀️ Try build successful - checks-actions
Build commit: 3d3fbc3 (3d3fbc3c91e604af5b9b333f21043027fab15906)

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bjorn3
bjorn3 reviewed Mar 31, 2024
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compiler/rustc_codegen_ssa/src/mir/block.rs
let target = targets.target_for_value(const_discr);
bx.br(helper.llbb_with_cleanup(self, target));
return;
};
}
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Note to self: cg_clif needs this too

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Finished benchmarking commit (3d3fbc3): comparison URL.

Overall result: ❌✅ regressions and improvements - ACTION NEEDED

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 a highly reliable metric that was used to determine the overall result at the top of this comment.

mean range count
Regressions ❌
(primary)		 0.6% [0.4%, 0.9%] 3
Regressions ❌
(secondary)		 - - 0
Improvements ✅
(primary)		 -0.6% [-1.3%, -0.2%] 6
Improvements ✅
(secondary)		 - - 0
All ❌✅ (primary) -0.2% [-1.3%, 0.9%] 9

Max RSS (memory usage)

Results

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)		 2.0% [0.2%, 3.3%] 3
Regressions ❌
(secondary)		 - - 0
Improvements ✅
(primary)		 -4.6% [-4.6%, -4.6%] 1
Improvements ✅
(secondary)		 - - 0
All ❌✅ (primary) 0.4% [-4.6%, 3.3%] 4

Cycles

Results

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)		 0.9% [0.8%, 1.1%] 2
Regressions ❌
(secondary)		 - - 0
Improvements ✅
(primary)		 -1.2% [-1.2%, -1.2%] 1
Improvements ✅
(secondary)		 - - 0
All ❌✅ (primary) 0.2% [-1.2%, 1.1%] 3

Binary size

Results

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)		 0.6% [0.1%, 2.0%] 62
Regressions ❌
(secondary)		 0.5% [0.2%, 2.7%] 18
Improvements ✅
(primary)		 -0.4% [-0.8%, -0.1%] 14
Improvements ✅
(secondary)		 - - 0
All ❌✅ (primary) 0.4% [-0.8%, 2.0%] 76

Bootstrap: 668.042s -> 671.806s (0.56%)
Artifact size: 315.71 MiB -> 315.75 MiB (0.01%)

@rustbot rustbot added perf-regression Performance regression. and removed S-waiting-on-perf Status: Waiting on a perf run to be completed. labels Mar 31, 2024
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