runtime: Coalescing calls to non-returning throw helpers?

Repro:

using System;

class Program
{
    public static void Main()
    {
        var arr = new int[20];
        var s0 = new Span<int>(arr, 0, 1);
        var s1 = new Span<int>(arr, 1, 1);
        var s2 = new Span<int>(arr, 2, 1);
        var s3 = new Span<int>(arr, 3, 1);
        var s4 = new Span<int>(arr, 4, 1);
        var s5 = new Span<int>(arr, 5, 1);
    }
}

The generated asm includes this at the end:

G_M45847_IG05:
       E84B8ECC5D           call     System.ThrowHelper:ThrowArgumentOutOfRangeException()

G_M45847_IG06:
       E8468ECC5D           call     System.ThrowHelper:ThrowArgumentOutOfRangeException()

G_M45847_IG07:
       E8418ECC5D           call     System.ThrowHelper:ThrowArgumentOutOfRangeException()

G_M45847_IG08:
       E83C8ECC5D           call     System.ThrowHelper:ThrowArgumentOutOfRangeException()

G_M45847_IG09:
       E8378ECC5D           call     System.ThrowHelper:ThrowArgumentOutOfRangeException()

G_M45847_IG10:
       E8328ECC5D           call     System.ThrowHelper:ThrowArgumentOutOfRangeException()
       CC                   int3

Can/should these be coalesced into a common call point?

category:cq theme:basic-cq skill-level:expert cost:medium

About this issue

Original URL
State: closed
Created 7 years ago
Comments: 20 (20 by maintainers)

Commits related to this issue

JIT: add pass to merge common throw helper calls Look for blocks with single statement noreturn calls, and try to reroute flow so there's just one block call that all predecessors target. Resolves #... — committed to AndyAyersMS/coreclr by AndyAyersMS 5 years ago
JIT: add pass to merge common throw helper calls Look for blocks with single statement noreturn calls, and try to reroute flow so there's just one block call that all predecessors target. Resolves #... — committed to AndyAyersMS/coreclr by AndyAyersMS 5 years ago
JIT: add pass to merge common throw helper calls (#27113) Look for blocks with single statement noreturn calls, and try to reroute flow so there's just one block call that all predecessors target. ... — committed to dotnet/coreclr by AndyAyersMS 5 years ago

Most upvoted comments

Here’s a prototype SimpleThrowTailMerge that can merge many common throw helper blocks.

Jit-Diffs reports:

Total bytes of diff: -39926 (-0.10% of base)
    diff is an improvement.

Top file improvements by size (bytes):
       -7162 : System.Private.CoreLib.dasm (-0.16% of base)
       -4440 : Microsoft.CodeAnalysis.VisualBasic.dasm (-0.08% of base)
       -4345 : System.Memory.dasm (-1.87% of base)
       -2488 : CommandLine.dasm (-0.56% of base)
       -2015 : Microsoft.CodeAnalysis.dasm (-0.12% of base)

82 total files with size differences (82 improved, 0 regressed), 47 unchanged.

Top method regressions by size (bytes):
         111 ( 5.69% of base) : System.Memory.dasm - SequenceReader`1:TryReadToSlow(byref,struct,struct,int,bool):bool:this (2 methods)
          87 (14.19% of base) : System.Security.Cryptography.Algorithms.dasm - PasswordBasedEncryption:Pbes2Decrypt(struct,struct,struct,struct,struct):int
          87 (14.19% of base) : System.Security.Cryptography.Cng.dasm - PasswordBasedEncryption:Pbes2Decrypt(struct,struct,struct,struct,struct):int
          78 (15.82% of base) : System.Memory.dasm - SequenceReader`1:TryReadToSlow(byref,struct,bool):bool:this
          56 ( 5.15% of base) : System.Security.Cryptography.Algorithms.dasm - KeyFormatHelper:WriteEncryptedPkcs8(struct,struct,ref,ref):ref

Top method improvements by size (bytes):
        -438 (-4.46% of base) : System.Memory.dasm - ReadOnlySequenceDebugView`1:.ctor(struct):this (7 methods)
        -396 (-5.97% of base) : Microsoft.CodeAnalysis.dasm - ArrayBuilderExtensions:SelectAsArray(ref,ref):struct (7 methods)
        -390 (-6.95% of base) : System.Memory.dasm - SequenceReader`1:TryCopyMultisegment(struct):bool:this (6 methods)
        -294 (-1.13% of base) : Microsoft.CodeAnalysis.dasm - AsyncQueue`1:WithCancellation(ref,struct):ref (49 methods)
        -294 (-1.80% of base) : System.Linq.Parallel.dasm - ParallelQuery`1:OfType():ref:this (49 methods)

Top method regressions by size (percentage):
          78 (15.82% of base) : System.Memory.dasm - SequenceReader`1:TryReadToSlow(byref,struct,bool):bool:this
          87 (14.19% of base) : System.Security.Cryptography.Algorithms.dasm - PasswordBasedEncryption:Pbes2Decrypt(struct,struct,struct,struct,struct):int
          87 (14.19% of base) : System.Security.Cryptography.Cng.dasm - PasswordBasedEncryption:Pbes2Decrypt(struct,struct,struct,struct,struct):int
          12 ( 9.52% of base) : System.Text.RegularExpressions.dasm - <>c:<AddConcatenate>b__78_0(struct,struct):this
          27 ( 8.79% of base) : System.Net.Http.dasm - Http2ReadStream:ReadAsync(struct,struct):struct:this

Top method improvements by size (percentage):
         -56 (-17.50% of base) : Microsoft.CodeAnalysis.VisualBasic.dasm - LookupResult:CompactSymbols(int):this
        -278 (-16.27% of base) : System.Reflection.Metadata.dasm - MetadataBuilder:GetRowCounts():struct:this
         -45 (-16.25% of base) : System.Private.CoreLib.dasm - Decimal:ToDecimal(struct):struct
         -56 (-16.18% of base) : Microsoft.CodeAnalysis.dasm - ExceptionHandlerContainerScope:CloseScope(ref):this
         -14 (-14.89% of base) : System.Security.Cryptography.Encoding.dasm - ThrowHelper:ValidateTransformBlock(ref,int,int,int)

1781 total methods with size differences (1756 improved, 25 regressed), 201163 unchanged.

The size win is modest, though still perhaps worth pursuing.

We might consider handling more general cases like BBJ_THROW blocks – not clear how often users write the exact same throw constructs in a method or across an inline complex.
Probably should to generalize the map key to include EH Region.
I haven’t looked at diffs extensively yet. Might be missing more cases than I realize.
Don’t expect regressions so will have to drill into those.
Might want to move this transformation earlier in the phase order to remove IR sooner.

AndyAyersMS on Oct 9, 2019