static void Test(int x)
{
switch (x)
{
case 1:
Console.WriteLine(x == 1);
break;
case 2:
Console.WriteLine(x == 2);
break;
case 3:
Console.WriteLine(x == 3);
break;
}
}Currently, JIT can't fold these x == y checks, but should be able to. This is a minimal repro for a popular case when Span/Array Length is used for switch and then all legs use that span.
For example, any attempt to remove unsafe code from the following function will hit regressions because of it:
|
[MethodImpl(MethodImplOptions.AggressiveInlining)] |
|
public static ulong GetKey(ReadOnlySpan<byte> name) |
|
{ |
|
ref byte reference = ref MemoryMarshal.GetReference(name); |
|
int length = name.Length; |
|
ulong key = (ulong)(byte)length << 56; |
|
|
|
switch (length) |
|
{ |
|
case 0: goto ComputedKey; |
|
case 1: goto OddLength; |
|
case 2: key |= Unsafe.ReadUnaligned<ushort>(ref reference); goto ComputedKey; |
|
case 3: key |= Unsafe.ReadUnaligned<ushort>(ref reference); goto OddLength; |
|
case 4: key |= Unsafe.ReadUnaligned<uint>(ref reference); goto ComputedKey; |
|
case 5: key |= Unsafe.ReadUnaligned<uint>(ref reference); goto OddLength; |
|
case 6: key |= Unsafe.ReadUnaligned<uint>(ref reference) | (ulong)Unsafe.ReadUnaligned<ushort>(ref Unsafe.Add(ref reference, 4)) << 32; goto ComputedKey; |
|
case 7: key |= Unsafe.ReadUnaligned<uint>(ref reference) | (ulong)Unsafe.ReadUnaligned<ushort>(ref Unsafe.Add(ref reference, 4)) << 32; goto OddLength; |
|
default: key |= Unsafe.ReadUnaligned<ulong>(ref reference) & 0x00ffffffffffffffL; goto ComputedKey; |
Currently, JIT can't fold these
x == ychecks, but should be able to. This is a minimal repro for a popular case when Span/Array Length is used for switch and then all legs use that span.For example, any attempt to remove unsafe code from the following function will hit regressions because of it:
runtime/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Metadata/PropertyRef.cs
Lines 52 to 69 in a37049f