[PATCH] Add default parameter to MCSymbol accessors to control IsUsed

[Vedant Kumar via llvm-commits]

Hi Rafael,

Sorry for the delay on this.

> I think that dates from the early days of MC. My understanding is that
> it was added just as a safety so that we have to reason about code
> like
> 
> foo = bar
> .long foo
> foo = zed
> .long foo
> 
> Should that produce two relocations with bar, two with foo or one each?

Here is what GAS does:

SYMBOL TABLE:
00000000 l    d  .text	00000000 .text
00000000 l    d  .data	00000000 .data
00000000 l    d  .bss	00000000 .bss
00000000         *UND*	00000000 bar
00000000         *UND*	00000000 zed

RELOCATION RECORDS FOR [.text]:
OFFSET   TYPE              VALUE 
00000000 R_386_32          bar
00000004 R_386_32          zed

Here is a different test that initially triggered this issue:

> foo = bar
> .long foo
> foo = bar
> .long foo


And here is GAS's output:

RELOCATION RECORDS FOR [.text]:
OFFSET   TYPE              VALUE 
00000000 R_386_32          bar
00000004 R_386_32          bar

With the patch I suggested, both of these examples just work with llvm-mc. Here's what the relocation table looks like on Darwin for comparison:

Relocation information (__TEXT,__text) 2 entries
address  pcrel length extern type    scattered symbolnum/value
00000004 0     2      1      0       0         1
00000000 0     2      1      0       0         1

This looks sane to me. I've updated the patch to get rid of the "invalid reassignment to non-absolute variable" error and fixed the test cases. Could you review it for any issues?

thanks
vedant

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