Emit switch for suitable 'or' patterns

[YairHalberstadt]

Version Used: master as of 3rd July

Steps to Reproduce:

Look at the IL for this code:

public class C 
{
    public bool M1(string a)
    {
        return (a is "1" or "2" or "3" or "4" or "5" or "6" or "7" or "8");
    }
    public bool M2(string a)
    {
        switch (a) 
        {
            case "1":
            case "2":
            case "3":
            case "4":
            case "5":
            case "6":
            case "7":
            case "8":
                return true;
            default:
                return false;       
        }
    }
    
    public bool M1(int a)
    {
        return (a is 1 or 2 or 3 or 4 or 5 or 6 or 7 or 8);
    }
    public bool M2(int a)
    {
        switch (a) 
        {
            case 1:
            case 2:
            case 3:
            case 4:
            case 5:
            case 6:
            case 7:
            case 8:
                return true;
            default:
                return false;       
        }
    }
}

IL:

.class private auto ansi '<Module>'
{
} // end of class <Module>

.class public auto ansi beforefieldinit C
    extends [System.Private.CoreLib]System.Object
{
    // Methods
    .method public hidebysig 
        instance bool M1 (
            string a
        ) cil managed 
    {
        // Method begins at RVA 0x2050
        // Code size 105 (0x69)
        .maxstack 2

        IL_0000: ldarg.1
        IL_0001: ldstr "1"
        IL_0006: call bool [System.Private.CoreLib]System.String::op_Equality(string, string)
        IL_000b: brtrue.s IL_0067

        IL_000d: ldarg.1
        IL_000e: ldstr "2"
        IL_0013: call bool [System.Private.CoreLib]System.String::op_Equality(string, string)
        IL_0018: brtrue.s IL_0067

        IL_001a: ldarg.1
        IL_001b: ldstr "3"
        IL_0020: call bool [System.Private.CoreLib]System.String::op_Equality(string, string)
        IL_0025: brtrue.s IL_0067

        IL_0027: ldarg.1
        IL_0028: ldstr "4"
        IL_002d: call bool [System.Private.CoreLib]System.String::op_Equality(string, string)
        IL_0032: brtrue.s IL_0067

        IL_0034: ldarg.1
        IL_0035: ldstr "5"
        IL_003a: call bool [System.Private.CoreLib]System.String::op_Equality(string, string)
        IL_003f: brtrue.s IL_0067

        IL_0041: ldarg.1
        IL_0042: ldstr "6"
        IL_0047: call bool [System.Private.CoreLib]System.String::op_Equality(string, string)
        IL_004c: brtrue.s IL_0067

        IL_004e: ldarg.1
        IL_004f: ldstr "7"
        IL_0054: call bool [System.Private.CoreLib]System.String::op_Equality(string, string)
        IL_0059: brtrue.s IL_0067

        IL_005b: ldarg.1
        IL_005c: ldstr "8"
        IL_0061: call bool [System.Private.CoreLib]System.String::op_Equality(string, string)
        IL_0066: ret

        IL_0067: ldc.i4.1
        IL_0068: ret
    } // end of method C::M1

    .method public hidebysig 
        instance bool M2 (
            string a
        ) cil managed 
    {
        // Method begins at RVA 0x20c8
        // Code size 240 (0xf0)
        .maxstack 2
        .locals init (
            [0] uint32
        )

        // sequence point: hidden
        IL_0000: ldarg.1
        IL_0001: call uint32 '<PrivateImplementationDetails>'::ComputeStringHash(string)
        IL_0006: stloc.0
        IL_0007: ldloc.0
        IL_0008: ldc.i4 856466825
        IL_000d: bgt.un.s IL_0047

        IL_000f: ldloc.0
        IL_0010: ldc.i4 822911587
        IL_0015: bgt.un.s IL_002f

        IL_0017: ldloc.0
        IL_0018: ldc.i4 806133968
        IL_001d: beq IL_00b2

        IL_0022: ldloc.0
        IL_0023: ldc.i4 822911587
        IL_0028: beq.s IL_00a3

        IL_002a: br IL_00ee

        IL_002f: ldloc.0
        IL_0030: ldc.i4 839689206
        IL_0035: beq IL_00d0

        IL_003a: ldloc.0
        IL_003b: ldc.i4 856466825
        IL_0040: beq.s IL_00c1

        IL_0042: br IL_00ee

        IL_0047: ldloc.0
        IL_0048: ldc.i4 906799682
        IL_004d: bgt.un.s IL_0064

        IL_004f: ldloc.0
        IL_0050: ldc.i4 873244444
        IL_0055: beq.s IL_0076

        IL_0057: ldloc.0
        IL_0058: ldc.i4 906799682
        IL_005d: beq.s IL_0094

        IL_005f: br IL_00ee

        IL_0064: ldloc.0
        IL_0065: ldc.i4 923577301
        IL_006a: beq.s IL_0085

        IL_006c: ldloc.0
        IL_006d: ldc.i4 1024243015
        IL_0072: beq.s IL_00df

        IL_0074: br.s IL_00ee

        IL_0076: ldarg.1
        IL_0077: ldstr "1"
        IL_007c: call bool [System.Private.CoreLib]System.String::op_Equality(string, string)
        IL_0081: brtrue.s IL_00ec

        IL_0083: br.s IL_00ee

        IL_0085: ldarg.1
        IL_0086: ldstr "2"
        IL_008b: call bool [System.Private.CoreLib]System.String::op_Equality(string, string)
        IL_0090: brtrue.s IL_00ec

        IL_0092: br.s IL_00ee

        IL_0094: ldarg.1
        IL_0095: ldstr "3"
        IL_009a: call bool [System.Private.CoreLib]System.String::op_Equality(string, string)
        IL_009f: brtrue.s IL_00ec

        IL_00a1: br.s IL_00ee

        IL_00a3: ldarg.1
        IL_00a4: ldstr "4"
        IL_00a9: call bool [System.Private.CoreLib]System.String::op_Equality(string, string)
        IL_00ae: brtrue.s IL_00ec

        IL_00b0: br.s IL_00ee

        IL_00b2: ldarg.1
        IL_00b3: ldstr "5"
        IL_00b8: call bool [System.Private.CoreLib]System.String::op_Equality(string, string)
        IL_00bd: brtrue.s IL_00ec

        IL_00bf: br.s IL_00ee

        IL_00c1: ldarg.1
        IL_00c2: ldstr "6"
        IL_00c7: call bool [System.Private.CoreLib]System.String::op_Equality(string, string)
        IL_00cc: brtrue.s IL_00ec

        IL_00ce: br.s IL_00ee

        IL_00d0: ldarg.1
        IL_00d1: ldstr "7"
        IL_00d6: call bool [System.Private.CoreLib]System.String::op_Equality(string, string)
        IL_00db: brtrue.s IL_00ec

        IL_00dd: br.s IL_00ee

        IL_00df: ldarg.1
        IL_00e0: ldstr "8"
        IL_00e5: call bool [System.Private.CoreLib]System.String::op_Equality(string, string)
        IL_00ea: brfalse.s IL_00ee

        IL_00ec: ldc.i4.1
        IL_00ed: ret

        IL_00ee: ldc.i4.0
        IL_00ef: ret
    } // end of method C::M2

    .method public hidebysig 
        instance bool M1 (
            int32 a
        ) cil managed 
    {
        // Method begins at RVA 0x21c4
        // Code size 35 (0x23)
        .maxstack 8

        IL_0000: ldarg.1
        IL_0001: ldc.i4.1
        IL_0002: beq.s IL_0021

        IL_0004: ldarg.1
        IL_0005: ldc.i4.2
        IL_0006: beq.s IL_0021

        IL_0008: ldarg.1
        IL_0009: ldc.i4.3
        IL_000a: beq.s IL_0021

        IL_000c: ldarg.1
        IL_000d: ldc.i4.4
        IL_000e: beq.s IL_0021

        IL_0010: ldarg.1
        IL_0011: ldc.i4.5
        IL_0012: beq.s IL_0021

        IL_0014: ldarg.1
        IL_0015: ldc.i4.6
        IL_0016: beq.s IL_0021

        IL_0018: ldarg.1
        IL_0019: ldc.i4.7
        IL_001a: beq.s IL_0021

        IL_001c: ldarg.1
        IL_001d: ldc.i4.8
        IL_001e: ceq
        IL_0020: ret

        IL_0021: ldc.i4.1
        IL_0022: ret
    } // end of method C::M1

    .method public hidebysig 
        instance bool M2 (
            int32 a
        ) cil managed 
    {
        // Method begins at RVA 0x21e8
        // Code size 10 (0xa)
        .maxstack 8

        // sequence point: hidden
        IL_0000: ldarg.1
        IL_0001: ldc.i4.1
        IL_0002: sub
        IL_0003: ldc.i4.7
        IL_0004: bgt.un.s IL_0008

        IL_0006: ldc.i4.1
        IL_0007: ret

        IL_0008: ldc.i4.0
        IL_0009: ret
    } // end of method C::M2

    .method public hidebysig specialname rtspecialname 
        instance void .ctor () cil managed 
    {
        // Method begins at RVA 0x21f3
        // Code size 7 (0x7)
        .maxstack 8

        IL_0000: ldarg.0
        IL_0001: call instance void [System.Private.CoreLib]System.Object::.ctor()
        IL_0006: ret
    } // end of method C::.ctor

} // end of class C

.class private auto ansi sealed '<PrivateImplementationDetails>'
    extends [System.Private.CoreLib]System.Object
{
    .custom instance void [System.Private.CoreLib]System.Runtime.CompilerServices.CompilerGeneratedAttribute::.ctor() = (
        01 00 00 00
    )
    // Methods
    .method assembly hidebysig static 
        uint32 ComputeStringHash (
            string s
        ) cil managed 
    {
        // Method begins at RVA 0x21fc
        // Code size 44 (0x2c)
        .maxstack 2
        .locals init (
            [0] uint32,
            [1] int32
        )

        IL_0000: ldarg.0
        IL_0001: brfalse.s IL_002a

        IL_0003: ldc.i4 -2128831035
        IL_0008: stloc.0
        IL_0009: ldc.i4.0
        IL_000a: stloc.1
        IL_000b: br.s IL_0021
        // loop start (head: IL_0021)
            IL_000d: ldarg.0
            IL_000e: ldloc.1
            IL_000f: callvirt instance char [System.Private.CoreLib]System.String::get_Chars(int32)
            IL_0014: ldloc.0
            IL_0015: xor
            IL_0016: ldc.i4 16777619
            IL_001b: mul
            IL_001c: stloc.0
            IL_001d: ldloc.1
            IL_001e: ldc.i4.1
            IL_001f: add
            IL_0020: stloc.1

            IL_0021: ldloc.1
            IL_0022: ldarg.0
            IL_0023: callvirt instance int32 [System.Private.CoreLib]System.String::get_Length()
            IL_0028: blt.s IL_000d
        // end loop

        IL_002a: ldloc.0
        IL_002b: ret
    } // end of method '<PrivateImplementationDetails>'::ComputeStringHash

} // end of class <PrivateImplementationDetails>

Expected Behavior:
Same IL for both M1 and M2

Actual Behavior:
Differing IL for M1 and M2

[jcouv]

Tagging @stephentoub as FYI (since closed #58246 as duplicate of this)