dotnet/roslyn

Optimize pattern matching over large tuple literals

Open

#48,052 opened on Sep 25, 2020

View on GitHub
 (2 comments) (0 reactions) (0 assignees)C# (4,257 forks)batch import
Area-CompilersCode Gen QualityFeature - Pattern Matchinghelp wanted

Repository metrics

Stars
 (20,414 stars)
PR merge metrics
 (Avg merge 6d 17h) (256 merged PRs in 30d)

Description

Follow-up to #47878

Version Used: f33a0fd1d5e9e1387e2bc3879b0ee1b14bd0a5a7

Steps to Reproduce:

Compile the following program:

using System;
public class C
{
    public static void Main()
    {
        int x = (1, 2, 3, 4, 5, 6, 7, 8) switch
        {
            (1, 2, 3, 4, 5, 6, 7, 8) => 1,
            _ => -1,
        };
        Console.WriteLine(x);
    }
}

Expected Behavior: Emitted code does not use ValueTuple, except to throw SwitchExpressionException(object), if applicable. This is what is done for smaller tuple literals. The optimization in RewriteTupleInput instead creates locals for the fields of the tuple literal.

Actual Behavior: Emitted code uses ValueTuple:

{
  // Code size      110 (0x6e)
  .maxstack  9
  .locals init (int V_0,
                System.ValueTuple<int, int, int, int, int, int, int, System.ValueTuple<int>> V_1)
  IL_0000:  ldloca.s   V_1
  IL_0002:  ldc.i4.1
  IL_0003:  ldc.i4.2
  IL_0004:  ldc.i4.3
  IL_0005:  ldc.i4.4
  IL_0006:  ldc.i4.5
  IL_0007:  ldc.i4.6
  IL_0008:  ldc.i4.7
  IL_0009:  ldc.i4.8
  IL_000a:  newobj     ""System.ValueTuple<int>..ctor(int)""
  IL_000f:  call       ""System.ValueTuple<int, int, int, int, int, int, int, System.ValueTuple<int>>..ctor(int, int, int, int, int, int, int, System.ValueTuple<int>)""
  IL_0014:  ldloc.1
  IL_0015:  ldfld      ""int System.ValueTuple<int, int, int, int, int, int, int, System.ValueTuple<int>>.Item1""
  IL_001a:  ldc.i4.1
  IL_001b:  bne.un.s   IL_0065
  IL_001d:  ldloc.1
  IL_001e:  ldfld      ""int System.ValueTuple<int, int, int, int, int, int, int, System.ValueTuple<int>>.Item2""
  IL_0023:  ldc.i4.2
  IL_0024:  bne.un.s   IL_0065
  IL_0026:  ldloc.1
  IL_0027:  ldfld      ""int System.ValueTuple<int, int, int, int, int, int, int, System.ValueTuple<int>>.Item3""
  IL_002c:  ldc.i4.3
  IL_002d:  bne.un.s   IL_0065
  IL_002f:  ldloc.1
  IL_0030:  ldfld      ""int System.ValueTuple<int, int, int, int, int, int, int, System.ValueTuple<int>>.Item4""
  IL_0035:  ldc.i4.4
  IL_0036:  bne.un.s   IL_0065
  IL_0038:  ldloc.1
  IL_0039:  ldfld      ""int System.ValueTuple<int, int, int, int, int, int, int, System.ValueTuple<int>>.Item5""
  IL_003e:  ldc.i4.5
  IL_003f:  bne.un.s   IL_0065
  IL_0041:  ldloc.1
  IL_0042:  ldfld      ""int System.ValueTuple<int, int, int, int, int, int, int, System.ValueTuple<int>>.Item6""
  IL_0047:  ldc.i4.6
  IL_0048:  bne.un.s   IL_0065
  IL_004a:  ldloc.1
  IL_004b:  ldfld      ""int System.ValueTuple<int, int, int, int, int, int, int, System.ValueTuple<int>>.Item7""
  IL_0050:  ldc.i4.7
  IL_0051:  bne.un.s   IL_0065
  IL_0053:  ldloc.1
  IL_0054:  ldfld      ""System.ValueTuple<int> System.ValueTuple<int, int, int, int, int, int, int, System.ValueTuple<int>>.Rest""
  IL_0059:  ldfld      ""int System.ValueTuple<int>.Item1""
  IL_005e:  ldc.i4.8
  IL_005f:  bne.un.s   IL_0065
  IL_0061:  ldc.i4.1
  IL_0062:  stloc.0
  IL_0063:  br.s       IL_0067
  IL_0065:  ldc.i4.m1
  IL_0066:  stloc.0
  IL_0067:  ldloc.0
  IL_0068:  call       ""void System.Console.WriteLine(int)""
  IL_006d:  ret
}

Contributor guide