On Mon, Jul 02, 2018 at 09:44:04AM +0200, Richard Biener wrote:
> Given the array has size i + 1 it's upper bound should be 'i' and 'i'
> should be available via DW_OP_[GNU_]entry_value.
>
> I see it is
>
> <175> DW_AT_upper_bound : 10 byte block: 75 1 8 20 24 8 20 26 31
> 1c (DW_OP_breg5 (rdi): 1; DW_OP_const1u: 32; DW_OP_shl;
> DW_OP_const1u: 32; DW_OP_shra; DW_OP_lit1; DW_OP_minus)
>
> and %rdi is 1. Not sure why gdb fails to print it's length. Yes, the
> storage itself doesn't have a location but the
> type specifies the size.
>
> (gdb) ptype a
> type = char [variable length]
> (gdb) p sizeof(a)
> $3 = 0
>
> this looks like a gdb bug to me?
>
> Btw, the location expression looks odd, if I deciper it correctly
> we end up with ((%rdi << 32) >> 32) - 1 which computes to 4
> but the upper bound should be 5. The GIMPLE debug stmts compute
> the upper bound as (sizetype)((long)(i_1(D) + 1) - 1)
The << 32 >> 32 is sign extension. And yes, for f1 I don't see why
DW_OP_GNU_entry_value shouldn't work, i in main is needed for the call to
f2, so needs to live in some register or memory in that function until the
second call. For f2 i is needed after the bar call for the a[i + 4] read,
worst case in form of precomputed i + 4, but that is reversible op.
Jakub
