[llvm] r175270 - Teach InstCombine to work with smaller legal types in icmp (shl %v, C1), C2

[Arnaud de Grandmaison]

Hi Benjamin and Duncan,

Attached is a patch proposal to fix my previous commit :

 - It now combines only if the icmp is the unique use of the shl.
 - It still does not check for legality of the type on the target, but it at 
least don't do the combining if the resulting type has an odd-width.

Let me know if this looks reasonable to you.

Cheers,
--
Arnaud

On Saturday 09 March 2013 11:08:07 Benjamin Kramer wrote:
> On 15.02.2013, at 15:35, Arnaud A. de Grandmaison <arnaud.adegm at gmail.com> 
wrote:
> > Author: aadg
> > Date: Fri Feb 15 08:35:47 2013
> > New Revision: 175270
> > 
> > URL: http://llvm.org/viewvc/llvm-project?rev=175270&view=rev
> > Log:
> > Teach InstCombine to work with smaller legal types in icmp (shl %v, C1),
> > C2
> 
> It says legal types, but the code never actually checks for legality.
> Combined with the not checking for multiple uses on the shift you're
> introducing potentially expensive operations here.
> 
> The attached test case (extracted from scimark) shows a case where your
> patch adds a trunc to i61.
> 
> - Ben
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