[llvm-commits] Thumb2 and-tst peephole optimization

[Gabor Greif]

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Hi all,

I am entering deeper waters with this patch, so I'd better put it
up to review...

I managed to eliminate the 'tst.w' instruction after a thumb2 'and'
by converting the latter to 'andS'.

Unfortunately the transformation is all but straightforward:

the 'tst.t' feeds on a register that is also ARM::COPYed and ends
up as the register argument to the 'and'.
So we have look through those copies to find the 'and'.
I am unsure whether I have gotten the logic right, as I want
to avoid a wildly branching algorithm and so I look for the
'and' only immediately behind the COPY.

Any hint how to get this coded up elegantly and efficiently
is welcome. The patch is attached.

Cheers,

	Gabor