R600: Add BFE DAG combines

[Matt Arsenault]

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.