MaybeImprove MaybeUninit

[saethlin]

I'm investigating possible solutions to #139355.

[saethlin]

@bors try @rust-timer queue

[bors]

⌛ Trying commit 1e1bc5f with merge 6b3cc92...

[rust-log-analyzer]

The job aarch64-gnu-llvm-19-1 failed! Check out the build log: (web) (plain)

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

failures:

---- [codegen] tests/codegen/maybeuninit-rvo.rs stdout ----

error: verification with 'FileCheck' failed
status: exit status: 1
command: "/usr/lib/llvm-19/bin/FileCheck" "--input-file" "/checkout/obj/build/aarch64-unknown-linux-gnu/test/codegen/maybeuninit-rvo/maybeuninit-rvo.ll" "/checkout/tests/codegen/maybeuninit-rvo.rs" "--check-prefix=CHECK" "--allow-unused-prefixes" "--dump-input-context" "100"
stdout: none
--- stderr -------------------------------
/checkout/tests/codegen/maybeuninit-rvo.rs:14:16: error: CHECK-NOT: excluded string found in input
 // CHECK-NOT: call void @llvm.memcpy.
               ^
/checkout/obj/build/aarch64-unknown-linux-gnu/test/codegen/maybeuninit-rvo/maybeuninit-rvo.ll:13:2: note: found here
 call void @llvm.memcpy.p0.p0.i64(ptr noundef nonnull align 1 dereferenceable(1000) %_0, ptr noundef nonnull align 1 dereferenceable(1000) %x, i64 1000, i1 false)
 ^~~~~~~~~~~~~~~~~~~~~~~
/checkout/tests/codegen/maybeuninit-rvo.rs:28:16: error: CHECK-NOT: excluded string found in input
 // CHECK-NOT: call void @llvm.memcpy.
               ^
/checkout/obj/build/aarch64-unknown-linux-gnu/test/codegen/maybeuninit-rvo/maybeuninit-rvo.ll:25:2: note: found here
 call void @llvm.memcpy.p0.p0.i64(ptr noundef nonnull align 1 dereferenceable(1000) %_0, ptr noundef nonnull align 1 dereferenceable(1000) %x, i64 1000, i1 false)
 ^~~~~~~~~~~~~~~~~~~~~~~

Input file: /checkout/obj/build/aarch64-unknown-linux-gnu/test/codegen/maybeuninit-rvo/maybeuninit-rvo.ll
Check file: /checkout/tests/codegen/maybeuninit-rvo.rs

-dump-input=help explains the following input dump.

Input was:
<<<<<<
        1: ; ModuleID = 'maybeuninit_rvo.85baa64fab381482-cgu.0' 
        2: source_filename = "maybeuninit_rvo.85baa64fab381482-cgu.0" 
        3: target datalayout = "e-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128-Fn32" 
        4: target triple = "aarch64-unknown-linux-gnu" 
        5:  
        6: ; maybeuninit_rvo::new_from_uninit 
        7: ; Function Attrs: nounwind uwtable 
        8: define void @_ZN15maybeuninit_rvo15new_from_uninit17h3bb6bd9c8758d8a5E(ptr dead_on_unwind noalias nocapture noundef writable writeonly sret([1000 x i8]) align 1 dereferenceable(1000) %_0) unnamed_addr #0 { 
        9: start: 
       10:  %x = alloca [1000 x i8], align 1 
       11:  call void @llvm.lifetime.start.p0(i64 1000, ptr nonnull %x) 
       12:  call void @init(ptr noundef nonnull %x) #4 
       13:  call void @llvm.memcpy.p0.p0.i64(ptr noundef nonnull align 1 dereferenceable(1000) %_0, ptr noundef nonnull align 1 dereferenceable(1000) %x, i64 1000, i1 false) 
not:14      !~~~~~~~~~~~~~~~~~~~~~~                                                                                                                                            error: no match expected
       14:  call void @llvm.lifetime.end.p0(i64 1000, ptr nonnull %x) 
       15:  ret void 
       16: } 
       17:  
       18: ; maybeuninit_rvo::new_from_uninit_unwind 
       19: ; Function Attrs: uwtable 
       20: define void @_ZN15maybeuninit_rvo22new_from_uninit_unwind17hb427b69ebf77e7d4E(ptr dead_on_unwind noalias nocapture noundef writable writeonly sret([1000 x i8]) align 1 dereferenceable(1000) %_0) unnamed_addr #1 { 
       21: start: 
       22:  %x = alloca [1000 x i8], align 1 
       23:  call void @llvm.lifetime.start.p0(i64 1000, ptr nonnull %x) 
       24:  call void @init_unwind(ptr noundef nonnull %x) 
       25:  call void @llvm.memcpy.p0.p0.i64(ptr noundef nonnull align 1 dereferenceable(1000) %_0, ptr noundef nonnull align 1 dereferenceable(1000) %x, i64 1000, i1 false) 
not:28      !~~~~~~~~~~~~~~~~~~~~~~                                                                                                                                            error: no match expected
       26:  call void @llvm.lifetime.end.p0(i64 1000, ptr nonnull %x) 
       27:  ret void 
       28: } 
       29:  
       30: ; Function Attrs: mustprogress nocallback nofree nosync nounwind willreturn memory(argmem: readwrite) 
       31: declare void @llvm.lifetime.start.p0(i64 immarg, ptr nocapture) #2 
       32:  
       33: ; Function Attrs: mustprogress nocallback nofree nounwind willreturn memory(argmem: readwrite) 
       34: declare void @llvm.memcpy.p0.p0.i64(ptr noalias nocapture writeonly, ptr noalias nocapture readonly, i64, i1 immarg) #3 
       35:  
       36: ; Function Attrs: nounwind uwtable 
       37: declare void @init(ptr noundef) unnamed_addr #0 
       38:  
       39: ; Function Attrs: mustprogress nocallback nofree nosync nounwind willreturn memory(argmem: readwrite) 
       40: declare void @llvm.lifetime.end.p0(i64 immarg, ptr nocapture) #2 
       41:  
       42: ; Function Attrs: uwtable 
       43: declare void @init_unwind(ptr noundef) unnamed_addr #1 
       44:  
       45: attributes #0 = { nounwind uwtable "frame-pointer"="non-leaf" "probe-stack"="inline-asm" "target-cpu"="generic" "target-features"="+v8a,+outline-atomics" } 
       46: attributes #1 = { uwtable "frame-pointer"="non-leaf" "probe-stack"="inline-asm" "target-cpu"="generic" "target-features"="+v8a,+outline-atomics" } 
       47: attributes #2 = { mustprogress nocallback nofree nosync nounwind willreturn memory(argmem: readwrite) } 
       48: attributes #3 = { mustprogress nocallback nofree nounwind willreturn memory(argmem: readwrite) } 
       49: attributes #4 = { nounwind } 
       50:  
       51: !llvm.module.flags = !{!0} 
       52: !llvm.ident = !{!1} 
       53:  
       54: !0 = !{i32 8, !"PIC Level", i32 2} 
       55: !1 = !{!"rustc version 1.89.0-nightly (843d46a22 2025-06-21)"} 
>>>>>>
------------------------------------------

[bors]

☀️ Try build successful - checks-actions
Build commit: 6b3cc92 (6b3cc9235e039b02dec997d63bec6109b13b694e)

[rust-timer]

Finished benchmarking commit (6b3cc92): 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)	0.3%	[0.1%, 0.8%]	20
Regressions ❌ (secondary)	0.3%	[0.2%, 0.3%]	7
Improvements ✅ (primary)	-4.8%	[-4.8%, -4.8%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.0%	[-4.8%, 0.8%]	21

Max RSS (memory usage)

Results (primary 0.1%, secondary 2.1%)

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

	mean	range	count
Regressions ❌ (primary)	2.5%	[2.2%, 2.9%]	2
Regressions ❌ (secondary)	2.1%	[2.1%, 2.1%]	1
Improvements ✅ (primary)	-4.8%	[-4.8%, -4.8%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.1%	[-4.8%, 2.9%]	3

Cycles

Results (primary -3.2%, secondary 7.3%)

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

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	7.3%	[7.3%, 7.3%]	1
Improvements ✅ (primary)	-3.2%	[-3.2%, -3.2%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-3.2%	[-3.2%, -3.2%]	1

Binary size

Results (primary 0.1%, secondary 0.0%)

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

	mean	range	count
Regressions ❌ (primary)	0.1%	[0.0%, 0.4%]	28
Regressions ❌ (secondary)	0.0%	[0.0%, 0.1%]	6
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-0.0%	[-0.0%, -0.0%]	1
All ❌✅ (primary)	0.1%	[0.0%, 0.4%]	28

Bootstrap: 690.042s -> 692.595s (0.37%)
Artifact size: 371.86 MiB -> 372.01 MiB (0.04%)