JIT: Incorrect last use propagation for implicit byrefs when undoing promotion #80488
Description
The propagation done at
runtime/src/coreclr/jit/morph.cpp
Lines 4785 to 4790 in 97cb762
GTF_VAR_DEATH on a promoted struct local if any of its fields are dying, but we can only know that the implicit byref local is dying if all of its fields are. Noticed this while trying to revive #78818.
using System;
using System.Runtime.CompilerServices;
class EarlyLiveness_ImplicitByRefPropagation
{
static int Main(string[] args)
{
int code = Foo(new S16 { F1 = 100 });
if (code != 100)
{
Console.WriteLine("FAIL: Returned {0}", code);
}
return code;
}
[MethodImpl(MethodImplOptions.NoInlining)]
private static int Foo(S16 s)
{
Bar(s);
return (int)s.F1;
}
[MethodImpl(MethodImplOptions.NoInlining)]
private static void Bar(S16 s)
{
s.F1 = 12345;
Consume(s);
}
[MethodImpl(MethodImplOptions.NoInlining)]
private static void Consume(S16 s) { }
private struct S16
{
public long F0, F1;
}
}