[LLVMdev] Simple question on sign

[Eli Friedman]

On Wed, Feb 22, 2012 at 4:28 PM, Ryan Taylor <ryta1203 at gmail.com> wrote:
On Wed, Feb 22, 2012 at 4:28 PM, Ryan Taylor <ryta1203 at gmail.com> wrote:
> How do you determine if a shift is signed or not?
>
> ashr = always signed?

Essentially, yes.

> lshr = always unsigned?

Essentially, yes.

> shl = always signed?

Signed left shift and unsigned left shift are both shl.

http://llvm.org/docs/LangRef.html#i_shl describes the semantics of shifts.

> The CmpInst has the "isSigned()" function, but it appears that every other
> Instruction I've looked at doesn't seem to have this.

There isn't an isSigned() function because the query doesn't really
make sense.  LLVM IR doesn't in general track whether a value is
signed or unsigned.

-Eli