[PATCH] Teach Instcombine to use the nsw attribute for signed comparisons to 0 of (shl %v, Cst) or (mul %v, Cst)

[Duncan Sands]

Hi Arnaud,

On 17/03/13 18:11, Arnaud de Grandmaison wrote:
> The attached patch teaches InstCombine/visitICmpInstWithInstAndIntCst to
> optimize 'icmp pred (mul %v, Cst), 0' when the mul has the nsw attribute set.
>   The comparison can the be performed on the mul RHS.
>
> The patch also handles the case of the mul in strength reduced form : shl

it looks like this will transform

   %mul = mul nsw i32 %x, 0
   %cmp = icmp sgt i32 %mul, 0

into

   icmp sgt i32 %x, 0

which is wrong.

Ciao, Duncan.