Optimize Span.Slice by using IsKnownConstant for start = 0 #69193
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Tagging subscribers to this area: @dotnet/area-system-runtime Issue DetailsThere are numerous places in the runtime where we call We can use the IsKnownConstant helper and check for the condition start = 0 to avoid the extension to 64 bits. There's not a significant throughput improvement since zero-extensions are already fast, but it does provide the opportunity to be more conservative with register usage, and it eliminates wasteful codegen. These could give second-order performance and space saving benefits. Crossgen doesn't seem to be inlining this method across assemblies, but here's the diff just within corelib. Found 274 files with textual diffs.
Summary of Code Size diffs:
(Lower is better)
Total bytes of base: 37308702
Total bytes of diff: 37307222
Total bytes of delta: -1480 (-0.00 % of base)
Total relative delta: NaN
diff is an improvement.
relative diff is a regression.
Top file improvements (bytes):
-1480 : System.Private.CoreLib.dasm (-0.05% of base)
1 total files with Code Size differences (1 improved, 0 regressed), 271 unchanged.
Top method improvements (bytes):
-35 (-5.45% of base) : System.Private.CoreLib.dasm - System.Collections.Generic.ArraySortHelper`2:IntroSort(System.Span`1[System.Byte],System.Span`1[System.Byte],int,System.Collections.Generic.IComparer`1[System.Byte])
-35 (-5.40% of base) : System.Private.CoreLib.dasm - System.Collections.Generic.ArraySortHelper`2:IntroSort(System.Span`1[System.Double],System.Span`1[System.Double],int,System.Collections.Generic.IComparer`1[System.Double])
-35 (-5.41% of base) : System.Private.CoreLib.dasm - System.Collections.Generic.ArraySortHelper`2:IntroSort(System.Span`1[System.Int16],System.Span`1[System.Int16],int,System.Collections.Generic.IComparer`1[System.Int16])
-35 (-5.40% of base) : System.Private.CoreLib.dasm - System.Collections.Generic.ArraySortHelper`2:IntroSort(System.Span`1[System.Int32],System.Span`1[System.Int32],int,System.Collections.Generic.IComparer`1[System.Int32])
-35 (-5.40% of base) : System.Private.CoreLib.dasm - System.Collections.Generic.ArraySortHelper`2:IntroSort(System.Span`1[System.Int64],System.Span`1[System.Int64],int,System.Collections.Generic.IComparer`1[System.Int64])
-35 (-5.45% of base) : System.Private.CoreLib.dasm - System.Collections.Generic.ArraySortHelper`2:IntroSort(System.Span`1[System.SByte],System.Span`1[System.SByte],int,System.Collections.Generic.IComparer`1[System.SByte])
-35 (-5.40% of base) : System.Private.CoreLib.dasm - System.Collections.Generic.ArraySortHelper`2:IntroSort(System.Span`1[System.Single],System.Span`1[System.Single],int,System.Collections.Generic.IComparer`1[System.Single])
-35 (-5.41% of base) : System.Private.CoreLib.dasm - System.Collections.Generic.ArraySortHelper`2:IntroSort(System.Span`1[System.UInt16],System.Span`1[System.UInt16],int,System.Collections.Generic.IComparer`1[System.UInt16])
-35 (-5.40% of base) : System.Private.CoreLib.dasm - System.Collections.Generic.ArraySortHelper`2:IntroSort(System.Span`1[System.UInt32],System.Span`1[System.UInt32],int,System.Collections.Generic.IComparer`1[System.UInt32])
-35 (-5.40% of base) : System.Private.CoreLib.dasm - System.Collections.Generic.ArraySortHelper`2:IntroSort(System.Span`1[System.UInt64],System.Span`1[System.UInt64],int,System.Collections.Generic.IComparer`1[System.UInt64])
-24 (-1.69% of base) : System.Private.CoreLib.dasm - System.IO.PathHelper:TryExpandShortFileName(byref,System.String):System.String
-23 (-5.36% of base) : System.Private.CoreLib.dasm - System.Collections.Generic.ArraySortHelper`1:IntroSort(System.Span`1[System.Byte],int,System.Comparison`1[System.Byte])
-23 (-5.35% of base) : System.Private.CoreLib.dasm - System.Collections.Generic.ArraySortHelper`1:IntroSort(System.Span`1[System.Diagnostics.Tracing.EventProvider+SessionInfo],int,System.Comparison`1[System.Diagnostics.Tracing.EventProvider+SessionInfo])
-23 (-5.35% of base) : System.Private.CoreLib.dasm - System.Collections.Generic.ArraySortHelper`1:IntroSort(System.Span`1[System.Double],int,System.Comparison`1[System.Double])
-23 (-5.35% of base) : System.Private.CoreLib.dasm - System.Collections.Generic.ArraySortHelper`1:IntroSort(System.Span`1[System.Int16],int,System.Comparison`1[System.Int16])
-23 (-5.35% of base) : System.Private.CoreLib.dasm - System.Collections.Generic.ArraySortHelper`1:IntroSort(System.Span`1[System.Int32],int,System.Comparison`1[System.Int32])
-23 (-5.35% of base) : System.Private.CoreLib.dasm - System.Collections.Generic.ArraySortHelper`1:IntroSort(System.Span`1[System.Int64],int,System.Comparison`1[System.Int64])
-23 (-5.36% of base) : System.Private.CoreLib.dasm - System.Collections.Generic.ArraySortHelper`1:IntroSort(System.Span`1[System.SByte],int,System.Comparison`1[System.SByte])
-23 (-5.35% of base) : System.Private.CoreLib.dasm - System.Collections.Generic.ArraySortHelper`1:IntroSort(System.Span`1[System.Single],int,System.Comparison`1[System.Single])
-23 (-5.36% of base) : System.Private.CoreLib.dasm - System.Collections.Generic.ArraySortHelper`1:IntroSort(System.Span`1[System.Threading.Tasks.ConcurrentExclusiveSchedulerPair+ProcessingMode],int,System.Comparison`1[System.Threading.Tasks.ConcurrentExclusiveSchedulerPair+ProcessingMode])
Top method improvements (percentages):
-7 (-14.89% of base) : System.Private.CoreLib.dasm - System.Runtime.CompilerServices.DefaultInterpolatedStringHandler:get_Text():System.ReadOnlySpan`1[System.Char]:this
-7 (-14.89% of base) : System.Private.CoreLib.dasm - System.Text.ValueStringBuilder:AsSpan():System.ReadOnlySpan`1[System.Char]:this
-6 (-9.23% of base) : System.Private.CoreLib.dasm - System.Runtime.CompilerServices.DefaultInterpolatedStringHandler:ToString():System.String:this
-6 (-6.74% of base) : System.Private.CoreLib.dasm - System.MemoryExtensions:TrimEnd(System.ReadOnlySpan`1[System.Char],ushort):System.ReadOnlySpan`1[System.Char]
-5 (-6.41% of base) : System.Private.CoreLib.dasm - System.ReadOnlyMemory`1:Slice(int,int):System.ReadOnlyMemory`1[System.__Canon]:this
-5 (-6.41% of base) : System.Private.CoreLib.dasm - System.ReadOnlyMemory`1:Slice(int,int):System.ReadOnlyMemory`1[System.Byte]:this
-5 (-6.41% of base) : System.Private.CoreLib.dasm - System.ReadOnlyMemory`1:Slice(int,int):System.ReadOnlyMemory`1[System.Char]:this
-7 (-6.14% of base) : System.Private.CoreLib.dasm - System.Globalization.TimeSpanParse:ParseExactLiteral(byref,byref):bool
-6 (-6.12% of base) : System.Private.CoreLib.dasm - Kernel32:GetAndTrimString(System.Span`1[System.Char]):System.String
-17 (-5.94% of base) : System.Private.CoreLib.dasm - System.MemoryExtensions:TrimEnd(System.ReadOnlyMemory`1[System.Char]):System.ReadOnlyMemory`1[System.Char]
-6 (-5.71% of base) : System.Private.CoreLib.dasm - System.Text.ValueStringBuilder:AsSpan(bool):System.ReadOnlySpan`1[System.Char]:this
-10 (-5.49% of base) : System.Private.CoreLib.dasm - <>c:<ToLower>b__2_0(System.Span`1[System.Char],System.ValueTuple`2[System.String, System.Int32]):this
-10 (-5.49% of base) : System.Private.CoreLib.dasm - <>c:<ToUpper>b__3_0(System.Span`1[System.Char],System.ValueTuple`2[System.String, System.Int32]):this
-35 (-5.45% of base) : System.Private.CoreLib.dasm - System.Collections.Generic.ArraySortHelper`2:IntroSort(System.Span`1[System.Byte],System.Span`1[System.Byte],int,System.Collections.Generic.IComparer`1[System.Byte])
-35 (-5.45% of base) : System.Private.CoreLib.dasm - System.Collections.Generic.ArraySortHelper`2:IntroSort(System.Span`1[System.SByte],System.Span`1[System.SByte],int,System.Collections.Generic.IComparer`1[System.SByte])
-35 (-5.41% of base) : System.Private.CoreLib.dasm - System.Collections.Generic.ArraySortHelper`2:IntroSort(System.Span`1[System.Int16],System.Span`1[System.Int16],int,System.Collections.Generic.IComparer`1[System.Int16])
-35 (-5.41% of base) : System.Private.CoreLib.dasm - System.Collections.Generic.ArraySortHelper`2:IntroSort(System.Span`1[System.UInt16],System.Span`1[System.UInt16],int,System.Collections.Generic.IComparer`1[System.UInt16])
-35 (-5.40% of base) : System.Private.CoreLib.dasm - System.Collections.Generic.ArraySortHelper`2:IntroSort(System.Span`1[System.Double],System.Span`1[System.Double],int,System.Collections.Generic.IComparer`1[System.Double])
-35 (-5.40% of base) : System.Private.CoreLib.dasm - System.Collections.Generic.ArraySortHelper`2:IntroSort(System.Span`1[System.Int32],System.Span`1[System.Int32],int,System.Collections.Generic.IComparer`1[System.Int32])
-35 (-5.40% of base) : System.Private.CoreLib.dasm - System.Collections.Generic.ArraySortHelper`2:IntroSort(System.Span`1[System.Int64],System.Span`1[System.Int64],int,System.Collections.Generic.IComparer`1[System.Int64])
142 total methods with Code Size differences (142 improved, 0 regressed), 254461 unchanged.
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@GrabYourPitchforks given this method has This is likely a broader issue and one that ideally we would optimize when we have a constant or known positive value (such as |
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What do diffs look like for this when |
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FWIW, there were some concerns with this pattern the last time we tried to use it, see #67285 (comment) and #64821. It might not matter for methods that already have aggressive inlining, however. |
When start is the constant 0, it turns into the comparison |
I don't think this should be difficult to fix in the JIT (famous last words). |
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@jakobbotsch Opened #69200 to track. I'll move this PR to draft for now while that issue is being discussed. |
I didn't observe any crossgen diff changes for start != 0. I didn't crack open the tests in a debugger to observe runtime JIT behaviors. |
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Superseded by #69247. |
ghost
locked as resolved and limited conversation to collaborators
There are numerous places in the runtime where we call
Span<T>.Slice(0, ...). This currently incurs needless expense due to the length argument and _length field both being zero-extended to 64 bits before comparison.We can use the IsKnownConstant helper and check for the condition start = 0 to avoid the extension to 64 bits. There's not a significant throughput improvement since zero-extensions are already fast, but it does provide the opportunity to be more conservative with register usage, and it eliminates wasteful codegen. These could give second-order performance and space saving benefits.
Crossgen doesn't seem to be inlining this method across assemblies, but here's the diff just within corelib.
Found 274 files with textual diffs. Summary of Code Size diffs: (Lower is better) Total bytes of base: 37308702 Total bytes of diff: 37307222 Total bytes of delta: -1480 (-0.00 % of base) Total relative delta: NaN diff is an improvement. relative diff is a regression. Top file improvements (bytes): -1480 : System.Private.CoreLib.dasm (-0.05% of base) 1 total files with Code Size differences (1 improved, 0 regressed), 271 unchanged. Top method improvements (bytes): -35 (-5.45% of base) : System.Private.CoreLib.dasm - System.Collections.Generic.ArraySortHelper`2:IntroSort(System.Span`1[System.Byte],System.Span`1[System.Byte],int,System.Collections.Generic.IComparer`1[System.Byte]) -35 (-5.40% of base) : System.Private.CoreLib.dasm - System.Collections.Generic.ArraySortHelper`2:IntroSort(System.Span`1[System.Double],System.Span`1[System.Double],int,System.Collections.Generic.IComparer`1[System.Double]) -35 (-5.41% of base) : System.Private.CoreLib.dasm - System.Collections.Generic.ArraySortHelper`2:IntroSort(System.Span`1[System.Int16],System.Span`1[System.Int16],int,System.Collections.Generic.IComparer`1[System.Int16]) -35 (-5.40% of base) : System.Private.CoreLib.dasm - System.Collections.Generic.ArraySortHelper`2:IntroSort(System.Span`1[System.Int32],System.Span`1[System.Int32],int,System.Collections.Generic.IComparer`1[System.Int32]) -35 (-5.40% of base) : System.Private.CoreLib.dasm - System.Collections.Generic.ArraySortHelper`2:IntroSort(System.Span`1[System.Int64],System.Span`1[System.Int64],int,System.Collections.Generic.IComparer`1[System.Int64]) -35 (-5.45% of base) : System.Private.CoreLib.dasm - System.Collections.Generic.ArraySortHelper`2:IntroSort(System.Span`1[System.SByte],System.Span`1[System.SByte],int,System.Collections.Generic.IComparer`1[System.SByte]) -35 (-5.40% of base) : System.Private.CoreLib.dasm - System.Collections.Generic.ArraySortHelper`2:IntroSort(System.Span`1[System.Single],System.Span`1[System.Single],int,System.Collections.Generic.IComparer`1[System.Single]) -35 (-5.41% of base) : System.Private.CoreLib.dasm - System.Collections.Generic.ArraySortHelper`2:IntroSort(System.Span`1[System.UInt16],System.Span`1[System.UInt16],int,System.Collections.Generic.IComparer`1[System.UInt16]) -35 (-5.40% of base) : System.Private.CoreLib.dasm - System.Collections.Generic.ArraySortHelper`2:IntroSort(System.Span`1[System.UInt32],System.Span`1[System.UInt32],int,System.Collections.Generic.IComparer`1[System.UInt32]) -35 (-5.40% of base) : System.Private.CoreLib.dasm - System.Collections.Generic.ArraySortHelper`2:IntroSort(System.Span`1[System.UInt64],System.Span`1[System.UInt64],int,System.Collections.Generic.IComparer`1[System.UInt64]) -24 (-1.69% of base) : System.Private.CoreLib.dasm - System.IO.PathHelper:TryExpandShortFileName(byref,System.String):System.String -23 (-5.36% of base) : System.Private.CoreLib.dasm - System.Collections.Generic.ArraySortHelper`1:IntroSort(System.Span`1[System.Byte],int,System.Comparison`1[System.Byte]) -23 (-5.35% of base) : System.Private.CoreLib.dasm - System.Collections.Generic.ArraySortHelper`1:IntroSort(System.Span`1[System.Diagnostics.Tracing.EventProvider+SessionInfo],int,System.Comparison`1[System.Diagnostics.Tracing.EventProvider+SessionInfo]) -23 (-5.35% of base) : System.Private.CoreLib.dasm - System.Collections.Generic.ArraySortHelper`1:IntroSort(System.Span`1[System.Double],int,System.Comparison`1[System.Double]) -23 (-5.35% of base) : System.Private.CoreLib.dasm - System.Collections.Generic.ArraySortHelper`1:IntroSort(System.Span`1[System.Int16],int,System.Comparison`1[System.Int16]) -23 (-5.35% of base) : System.Private.CoreLib.dasm - System.Collections.Generic.ArraySortHelper`1:IntroSort(System.Span`1[System.Int32],int,System.Comparison`1[System.Int32]) -23 (-5.35% of base) : System.Private.CoreLib.dasm - System.Collections.Generic.ArraySortHelper`1:IntroSort(System.Span`1[System.Int64],int,System.Comparison`1[System.Int64]) -23 (-5.36% of base) : System.Private.CoreLib.dasm - System.Collections.Generic.ArraySortHelper`1:IntroSort(System.Span`1[System.SByte],int,System.Comparison`1[System.SByte]) -23 (-5.35% of base) : System.Private.CoreLib.dasm - System.Collections.Generic.ArraySortHelper`1:IntroSort(System.Span`1[System.Single],int,System.Comparison`1[System.Single]) -23 (-5.36% of base) : System.Private.CoreLib.dasm - System.Collections.Generic.ArraySortHelper`1:IntroSort(System.Span`1[System.Threading.Tasks.ConcurrentExclusiveSchedulerPair+ProcessingMode],int,System.Comparison`1[System.Threading.Tasks.ConcurrentExclusiveSchedulerPair+ProcessingMode]) Top method improvements (percentages): -7 (-14.89% of base) : System.Private.CoreLib.dasm - System.Runtime.CompilerServices.DefaultInterpolatedStringHandler:get_Text():System.ReadOnlySpan`1[System.Char]:this -7 (-14.89% of base) : System.Private.CoreLib.dasm - System.Text.ValueStringBuilder:AsSpan():System.ReadOnlySpan`1[System.Char]:this -6 (-9.23% of base) : System.Private.CoreLib.dasm - System.Runtime.CompilerServices.DefaultInterpolatedStringHandler:ToString():System.String:this -6 (-6.74% of base) : System.Private.CoreLib.dasm - System.MemoryExtensions:TrimEnd(System.ReadOnlySpan`1[System.Char],ushort):System.ReadOnlySpan`1[System.Char] -5 (-6.41% of base) : System.Private.CoreLib.dasm - System.ReadOnlyMemory`1:Slice(int,int):System.ReadOnlyMemory`1[System.__Canon]:this -5 (-6.41% of base) : System.Private.CoreLib.dasm - System.ReadOnlyMemory`1:Slice(int,int):System.ReadOnlyMemory`1[System.Byte]:this -5 (-6.41% of base) : System.Private.CoreLib.dasm - System.ReadOnlyMemory`1:Slice(int,int):System.ReadOnlyMemory`1[System.Char]:this -7 (-6.14% of base) : System.Private.CoreLib.dasm - System.Globalization.TimeSpanParse:ParseExactLiteral(byref,byref):bool -6 (-6.12% of base) : System.Private.CoreLib.dasm - Kernel32:GetAndTrimString(System.Span`1[System.Char]):System.String -17 (-5.94% of base) : System.Private.CoreLib.dasm - System.MemoryExtensions:TrimEnd(System.ReadOnlyMemory`1[System.Char]):System.ReadOnlyMemory`1[System.Char] -6 (-5.71% of base) : System.Private.CoreLib.dasm - System.Text.ValueStringBuilder:AsSpan(bool):System.ReadOnlySpan`1[System.Char]:this -10 (-5.49% of base) : System.Private.CoreLib.dasm - <>c:<ToLower>b__2_0(System.Span`1[System.Char],System.ValueTuple`2[System.String, System.Int32]):this -10 (-5.49% of base) : System.Private.CoreLib.dasm - <>c:<ToUpper>b__3_0(System.Span`1[System.Char],System.ValueTuple`2[System.String, System.Int32]):this -35 (-5.45% of base) : System.Private.CoreLib.dasm - System.Collections.Generic.ArraySortHelper`2:IntroSort(System.Span`1[System.Byte],System.Span`1[System.Byte],int,System.Collections.Generic.IComparer`1[System.Byte]) -35 (-5.45% of base) : System.Private.CoreLib.dasm - System.Collections.Generic.ArraySortHelper`2:IntroSort(System.Span`1[System.SByte],System.Span`1[System.SByte],int,System.Collections.Generic.IComparer`1[System.SByte]) -35 (-5.41% of base) : System.Private.CoreLib.dasm - System.Collections.Generic.ArraySortHelper`2:IntroSort(System.Span`1[System.Int16],System.Span`1[System.Int16],int,System.Collections.Generic.IComparer`1[System.Int16]) -35 (-5.41% of base) : System.Private.CoreLib.dasm - System.Collections.Generic.ArraySortHelper`2:IntroSort(System.Span`1[System.UInt16],System.Span`1[System.UInt16],int,System.Collections.Generic.IComparer`1[System.UInt16]) -35 (-5.40% of base) : System.Private.CoreLib.dasm - System.Collections.Generic.ArraySortHelper`2:IntroSort(System.Span`1[System.Double],System.Span`1[System.Double],int,System.Collections.Generic.IComparer`1[System.Double]) -35 (-5.40% of base) : System.Private.CoreLib.dasm - System.Collections.Generic.ArraySortHelper`2:IntroSort(System.Span`1[System.Int32],System.Span`1[System.Int32],int,System.Collections.Generic.IComparer`1[System.Int32]) -35 (-5.40% of base) : System.Private.CoreLib.dasm - System.Collections.Generic.ArraySortHelper`2:IntroSort(System.Span`1[System.Int64],System.Span`1[System.Int64],int,System.Collections.Generic.IComparer`1[System.Int64]) 142 total methods with Code Size differences (142 improved, 0 regressed), 254461 unchanged. --------------------------------------------------------------------------------