Simplify `slice::Iter::next` enough that it inlines #136771

scottmcm · 2025-02-09T11:00:05Z

Inspired by this zulip conversation: https://rust-lang.zulipchat.com/#narrow/channel/189540-t-compiler.2Fwg-mir-opt/topic/Feedback.20on.20a.20MIR.20optimization.20idea/near/498579990

Draft for now because it needs #136735 to get the codegen tests to pass.

rustbot · 2025-02-09T11:00:13Z

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scottmcm · 2025-02-09T11:05:21Z

Let's see whether it actually improves things:
@bors try @rust-timer queue

bors · 2025-02-09T11:06:31Z

⌛ Trying commit f7970b3 with merge 30df00cd8218095deb80cc6b913de02f5ae4a5b0...

Simplify `slice::Iter::next` enough that it inlines Inspired by this zulip conversation: <https://rust-lang.zulipchat.com/#narrow/channel/189540-t-compiler.2Fwg-mir-opt/topic/Feedback.20on.20a.20MIR.20optimization.20idea/near/498579990> Draft for now because it needs rust-lang#136735 to get the codegen tests to pass.

rust-log-analyzer · 2025-02-09T11:23:00Z

The job x86_64-gnu-llvm-18 failed! Check out the build log: (web) (plain)

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

#21 exporting to docker image format
#21 sending tarball 27.3s done
#21 DONE 33.7s
##[endgroup]
Setting extra environment values for docker:  --env ENABLE_GCC_CODEGEN=1 --env GCC_EXEC_PREFIX=/usr/lib/gcc/
[CI_JOB_NAME=x86_64-gnu-llvm-18]
debug: `DISABLE_CI_RUSTC_IF_INCOMPATIBLE` configured.
---
sccache: Starting the server...
##[group]Configure the build
configure: processing command line
configure: 
configure: build.configure-args := ['--build=x86_64-unknown-linux-gnu', '--llvm-root=/usr/lib/llvm-18', '--enable-llvm-link-shared', '--set', 'rust.randomize-layout=true', '--set', 'rust.thin-lto-import-instr-limit=10', '--enable-verbose-configure', '--enable-sccache', '--disable-manage-submodules', '--enable-locked-deps', '--enable-cargo-native-static', '--set', 'rust.codegen-units-std=1', '--set', 'dist.compression-profile=balanced', '--dist-compression-formats=xz', '--set', 'rust.lld=false', '--disable-dist-src', '--release-channel=nightly', '--enable-debug-assertions', '--enable-overflow-checks', '--enable-llvm-assertions', '--set', 'rust.verify-llvm-ir', '--set', 'rust.codegen-backends=llvm,cranelift,gcc', '--set', 'llvm.static-libstdcpp', '--enable-new-symbol-mangling']
configure: target.x86_64-unknown-linux-gnu.llvm-config := /usr/lib/llvm-18/bin/llvm-config
configure: llvm.link-shared     := True
configure: rust.randomize-layout := True
configure: rust.thin-lto-import-instr-limit := 10
---
failures:

---- [codegen] tests/codegen/issues/issue-37945.rs stdout ----

error: verification with 'FileCheck' failed
status: exit status: 1
command: "/usr/lib/llvm-18/bin/FileCheck" "--input-file" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/codegen/issues/issue-37945/issue-37945.ll" "/checkout/tests/codegen/issues/issue-37945.rs" "--check-prefix=CHECK" "--allow-unused-prefixes" "--dump-input-context" "100"
--- stderr -------------------------------
/checkout/tests/codegen/issues/issue-37945.rs:14:17: error: CHECK-NEXT: expected string not found in input
/checkout/tests/codegen/issues/issue-37945.rs:14:17: error: CHECK-NEXT: expected string not found in input
 // CHECK-NEXT: [[A:%.*]] = icmp ne ptr {{%xs.0|%xs.1}}, null
                ^
/checkout/obj/build/x86_64-unknown-linux-gnu/test/codegen/issues/issue-37945/issue-37945.ll:8:7: note: scanning from here
      ^
      ^
/checkout/obj/build/x86_64-unknown-linux-gnu/test/codegen/issues/issue-37945/issue-37945.ll:9:3: note: possible intended match here
 %_3.not = icmp eq ptr %xs.1, %xs.0
/checkout/tests/codegen/issues/issue-37945.rs:27:17: error: CHECK-NEXT: expected string not found in input
/checkout/tests/codegen/issues/issue-37945.rs:27:17: error: CHECK-NEXT: expected string not found in input
 // CHECK-NEXT: [[C:%.*]] = icmp ne ptr {{%xs.0|%xs.1}}, null
                ^
/checkout/obj/build/x86_64-unknown-linux-gnu/test/codegen/issues/issue-37945/issue-37945.ll:15:7: note: scanning from here
      ^
      ^
/checkout/obj/build/x86_64-unknown-linux-gnu/test/codegen/issues/issue-37945/issue-37945.ll:16:4: note: possible intended match here
 %_12.not = icmp eq ptr %xs.1, %xs.0

Input file: /checkout/obj/build/x86_64-unknown-linux-gnu/test/codegen/issues/issue-37945/issue-37945.ll
Check file: /checkout/tests/codegen/issues/issue-37945.rs


-dump-input=help explains the following input dump.
Input was:
<<<<<<
<<<<<<
           1: ; ModuleID = 'issue_37945.20c1cf91498ad042-cgu.0' 
           2: source_filename = "issue_37945.20c1cf91498ad042-cgu.0" 
           3: target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128" 
           5:  
           5:  
           6: ; Function Attrs: mustprogress nofree norecurse nosync nounwind nonlazybind willreturn memory(none) uwtable 
           7: define noundef zeroext i1 @is_empty_1(ptr noundef readnone %xs.0, ptr noundef nonnull readnone %xs.1) unnamed_addr #0 { 
           8: start: 
next:14'0           X error: no match found
           9:  %_3.not = icmp eq ptr %xs.1, %xs.0 
next:14'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
next:14'1       ?                                  possible intended match
          10:  ret i1 %_3.not 
next:14'0     ~~~~~~~~~~~~~~~~
          11: } 
next:14'0     ~~
next:14'0     ~
next:14'0     ~
          13: ; Function Attrs: mustprogress nofree norecurse nosync nounwind nonlazybind willreturn memory(none) uwtable 
next:14'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
          14: define noundef zeroext i1 @is_empty_2(ptr noundef readnone %xs.0, ptr noundef nonnull readnone %xs.1) unnamed_addr #0 { 
next:14'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
          15: start: 
next:27'0           X error: no match found
          16:  %_12.not = icmp eq ptr %xs.1, %xs.0 
next:27'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
next:27'1        ?                                  possible intended match
          17:  ret i1 %_12.not 
next:27'0     ~~~~~~~~~~~~~~~~~
          18: } 
next:27'0     ~~
next:27'0     ~
next:27'0     ~
          20: attributes #0 = { mustprogress nofree norecurse nosync nounwind nonlazybind willreturn memory(none) uwtable "probe-stack"="inline-asm" "target-cpu"="x86-64" } 
next:27'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
next:27'0     ~
next:27'0     ~
          22: !llvm.module.flags = !{!0, !1} 
next:27'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
          23: !llvm.ident = !{!2} 
next:27'0     ~~~~~~~~~~~~~~~~~~~~
next:27'0     ~
next:27'0     ~
          25: !0 = !{i32 8, !"PIC Level", i32 2} 
next:27'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
          26: !1 = !{i32 2, !"RtLibUseGOT", i32 1} 
next:27'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
          27: !2 = !{!"rustc version 1.86.0-nightly (1e1da50a0 2025-02-09)"} 
next:27'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
------------------------------------------

bors · 2025-02-09T12:58:41Z

☀️ Try build successful - checks-actions
Build commit: 30df00c (30df00cd8218095deb80cc6b913de02f5ae4a5b0)

rust-timer · 2025-02-09T15:26:04Z

Finished benchmarking commit (30df00c): 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)	0.4%	[0.4%, 0.4%]	1
Regressions ❌ (secondary)	9.4%	[9.4%, 9.4%]	1
Improvements ✅ (primary)	-0.6%	[-2.2%, -0.1%]	210
Improvements ✅ (secondary)	-0.5%	[-1.1%, -0.1%]	131
All ❌✅ (primary)	-0.6%	[-2.2%, 0.4%]	211

Max RSS (memory usage)

Results (primary -2.2%, secondary -2.5%)

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)	2.4%	[1.7%, 2.8%]	3
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-4.4%	[-8.5%, -2.4%]	6
Improvements ✅ (secondary)	-2.5%	[-2.5%, -2.5%]	1
All ❌✅ (primary)	-2.2%	[-8.5%, 2.8%]	9

Cycles

Results (primary -1.0%, 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)	4.6%	[4.6%, 4.6%]	1
Improvements ✅ (primary)	-1.0%	[-1.1%, -0.9%]	2
Improvements ✅ (secondary)	-1.1%	[-1.1%, -1.1%]	1
All ❌✅ (primary)	-1.0%	[-1.1%, -0.9%]	2

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)	0.5%	[0.0%, 5.0%]	28
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.2%	[-0.5%, -0.0%]	45
Improvements ✅ (secondary)	-0.1%	[-1.3%, -0.0%]	48
All ❌✅ (primary)	0.1%	[-0.5%, 5.0%]	73

Bootstrap: 780.488s -> 778.559s (-0.25%)
Artifact size: 329.04 MiB -> 329.26 MiB (0.06%)

Simplify slice::Iter::next enough that it inlines

f7970b3

rustbot assigned joboet Feb 9, 2025

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. T-libs Relevant to the library team, which will review and decide on the PR/issue. labels Feb 9, 2025

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rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Feb 9, 2025

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rustbot added perf-regression Performance regression. and removed S-waiting-on-perf Status: Waiting on a perf run to be completed. labels Feb 9, 2025

FractalFir mentioned this pull request Feb 9, 2025

[perf experiment] A MIR pass dedicated to optimizing common iterators #136745

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Simplify `slice::Iter::next` enough that it inlines #136771

Simplify `slice::Iter::next` enough that it inlines #136771

scottmcm commented Feb 9, 2025

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rust-timer commented Feb 9, 2025

Simplify slice::Iter::next enough that it inlines #136771

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Simplify slice::Iter::next enough that it inlines #136771

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scottmcm commented Feb 9, 2025

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bors commented Feb 9, 2025

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rust-timer commented Feb 9, 2025

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

Instruction count

Max RSS (memory usage)

Cycles

Binary size

Simplify `slice::Iter::next` enough that it inlines #136771

Simplify `slice::Iter::next` enough that it inlines #136771