[LLVMdev] Signed/Unsigned Instruction selection.

[Tim Northover]

> The sign information is no more available in the selection DAG.
> So how can I generate different instructions for binary operators with
> signed/unsigned operands in the assembler (e.g. mul/mulu)?

Instructions where it actually matters (assuming 2s-complement
representation) have different nodes in the DAG. If you look at
include/llvm/CodeGen/ISDOpcodes.h you'll see separate UDIV and SDIV
nodes, for example.

It only usually affects multiplications if you're doing an extend at
the same time (hence the MULHS, SMUL_LOHI and friends) or care about
overflow (hence SMULO/UMULO).

Cheers.

Tim.