The GNU assembler treats things like:
brasl %r14, 100
in the same way as:
brasl %r14, .+100
rather than as a branch to absolute address 100. We implemented this in
LLVM by creating an immediate operand rather than the usual expr operand,
and by handling immediate operands specially in the code emitter.
This was undesirable for (at least) three reasons:
- the specialness of immediate operands was exposed to the backend MC code,
rather than being limited to the assembler parser.
- in disassembly, an immediate operand really is an absolute address.
(Note that this means reassembling printed disassembly can't recreate
the original code.)
- it would interfere with any assembly manipulation that we might
try in future. E.g. operations like branch shortening can change
the relative position of instructions, but any code that updates
sym+offset addresses wouldn't update an immediate "100" operand
in the same way as an explicit ".+100" operand.
This patch changes the implementation so that the assembler creates
a "." label for immediate PC-relative operands, so that the operand
to the MCInst is always the absolute address. The patch also adds
some error checking of the offset.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@181773 91177308-0d34-0410-b5e6-96231b3b80d8
