llvm dev - Jan 2011 - [LLVMdev] Question about nsw and nuw flags

Hi everybody,

I saw that there are some instructions in the programs in which the flag nsw
or nuw is placed. I wonder what rules does LLVM follows to put these flags
in some instructions.


Best,

Douglas
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On Jan 12, 2011, at 11:31 AM, Douglas do Couto Teixeira wrote:
> Hi everybody,
> 
> I saw that there are some instructions in the programs in which the flag
nsw or nuw is placed. I wonder what rules does LLVM follows to put these flags
in some instructions.
Hi Douglas,

The canonical reference for these types of questions is the IR description,
here: http://llvm.org/docs/LangRef.html

-Chris

Douglas do Couto Teixeira <douglasdocouto <at> gmail.com>
writes:
> Hi everybody,I saw that there are some instructions in the programs in
which
the flag nsw or nuw is placed. I wonder what rules does LLVM follows to put
these flags in some instructions.Best,Douglas

Language requirements appears to drive their placement.  In C, "signed
int"
overflow produces a trap value and undefined behavior.  Thus, C "signed
int"
operations do not wrap on overflow and get tagged with "nsw" in the
LLVM IR.

Brian West