R600: Add BFE DAG combines

[Tom Stellard]

On Tue, May 13, 2014 at 03:52:17PM -0700, Matt Arsenault wrote:
> On 05/13/2014 03:47 PM, Tom Stellard wrote:
> > On Mon, May 12, 2014 at 11:46:39AM -0700, Matt Arsenault wrote:
> >> On Apr 25, 2014, at 1:57 PM, Matt Arsenault <arsenm2 at gmail.com> wrote:
> >>
> >>> These patches allow some simplifications of BFE nodes. I just noticed the instruction patterns aren’t actually trying to match the BFE pattern, but that can be fixed later
> >>>
> >>>
> >>> <0001-R600-Implement-computeMaskedBitsForTargetNode-for-BF.patch><0002-R600-Implement-ComputeNumSignBitsForTargetNode-for-B.patch><0003-R600-Add-dag-combine-for-BFE.patch><0004-R600-Try-to-convert-BFE-back-to-standard-bit-ops-whe.patch>
> >> Ping
> > Can you explain the purpose of patch #4?  I don't understand why we are
> > converting BFE back to bit ops.
> >
> > -Tom
> To allow the standard DAG combines to work. The cases that convert back 
> are already equivalent to a single standard opcode. Mostly I was seeing 
> redundant sign extensions, and replacing an equivalent BFE with 
> sign_extend_inreg would allow it to be removed.

So this only covers the case where we have used a BFE instrinsic that is
equivalent to sign_extend_inreg?

-Tom