[mono] Append -sroa and -instcombine to LLVM-JIT pass manager

[EgorBo]

Partially fixes #37449

static ReadOnlySpan<byte> Arr
{
    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    get => new byte[] {1, 2, 3, 4};
}

[MethodImpl(MethodImplOptions.NoInlining)]
public static byte GetByte(int i) => Arr[0];

Codegen for GetByte() in LLVM-JIT mode:

0000000000000000 <gram_GetByte__int_>:
<BB>:1
   0:   48 83 ec 28             sub    $0x28,%rsp
   4:   c5 f8 57 c0             vxorps %xmm0,%xmm0,%xmm0
   8:   c5 f8 29 04 24          vmovaps %xmm0,(%rsp)
   d:   48 b8 b0 bd 55 d2 3f    movabs $0x563fd255bdb0,%rax
  14:   56 00 00
  17:   48 89 04 24             mov    %rax,(%rsp)
  1b:   c7 44 24 08 04 00 00    movl   $0x4,0x8(%rsp)
  22:   00
  23:   48 8b 04 24             mov    (%rsp),%rax
  27:   48 89 44 24 10          mov    %rax,0x10(%rsp)
  2c:   8b 44 24 08             mov    0x8(%rsp),%eax
  30:   89 44 24 18             mov    %eax,0x18(%rsp)
  34:   8b 44 24 0c             mov    0xc(%rsp),%eax
  38:   89 44 24 1c             mov    %eax,0x1c(%rsp)
  3c:   83 7c 24 18 00          cmpl   $0x0,0x18(%rsp)
  41:   74 0c                   je     4f <gram_GetByte__int_+0x4f>
  43:   48 8b 44 24 10          mov    0x10(%rsp),%rax
  48:   8a 00                   mov    (%rax),%al
  4a:   48 83 c4 28             add    $0x28,%rsp
  4e:   c3                      retq
  4f:   48 b8 d0 ae 42 d2 3f    movabs $0x563fd242aed0,%rax
  56:   56 00 00
  59:   bf 02 01 00 00          mov    $0x102,%edi
  5e:   ff 10                   callq  *(%rax)

Codegen after I appended -sroa -instcombine (makes sense to add/move extra -simplifycfg for hygiene) to the end of LLVM passes list:

0000000000000000 <gram_GetByte__int_>:
<BB>:1
   0:   48 b8 d0 ef a6 ba 31    movabs $0x5631baa6efd0,%rax
   7:   56 00 00
   a:   8a 00                   mov    (%rax),%al
   c:   c3                      retq

This https://godbolt.org/z/YKjzsV link explains motivation (on the left is the "final" LLVM IR our llvm-jit produces after the default optimizations). Zoltan noticed that LLVM-AOT where we use opt -O2 instead of custom pass order optimized that code perfectly.

The other issue remains: for some reason we don't inline get_Arr() without AggressiveInlining, coreclr does inline it:

Successfully inlined Program:get_Arr():System.ReadOnlySpan`1[Byte] (12 IL bytes) (depth 1) [below ALWAYS_INLINE size]

[ghost]

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[vargaz]

We don't inline get_Arr () because it hits the inlining cost limit of 60.