dotnet/roslyn
Int64 indices are silently truncated when used to access MD array elements
Aberta
#30.648 aberto em 22 de out. de 2018
Area-CompilersBughelp wanted
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Description
The following code should produce an exception (IndexOutOfRangeException but OverflowException would do too I guess) but it does not:
static void Main() => Test(new int[42, 42], 41, 41);
[MethodImpl(MethodImplOptions.NoInlining)]
static void Test(int[,] a, long x, long y) => a[x | (0x12345678L << 32), y] = 42;
The generated IL code is:
ldarg.0
ldarg.1
ldc.i8 0x1234567800000000
or
conv.ovf.i
ldarg.2
conv.ovf.i
ldc.i4.s 42
call instance void int32[0..., 0...]::Set(int32,int32,int32)
The spec appears to be silent about this case. From the generated code it looks like the intention was to handle this case by using a checked cast, the same is done with SZ arrays.
There must have been some confusion with ldelem. That one accepts both int32 and native int but MD array accessors support only int32 indices and passing a native int argument in this case would result in silent truncation. That conv.ovf.i should really be conv.ovf.i4.
Reproduced with VS 15.8.7 but I'd guess that the problem is much older.