[PATCH] D144789: [DAG] Match select(icmp(x,y),sub(x,y),sub(y,x)) -> abd(x,y) patterns

[Simon Pilgrim via Phabricator via llvm-commits]

RKSimon added inline comments.


================
Comment at: llvm/test/CodeGen/X86/abds-vector-128.ll:1116
 ; SSE42-NEXT:    pcmpeqd %xmm0, %xmm0
 ; SSE42-NEXT:    pxor %xmm1, %xmm0
+; SSE42-NEXT:    paddq %xmm4, %xmm0
----------------
RKSimon wrote:
> goldstein.w.n wrote:
> > the:
> > ```
> > pcmpgtq %xmm2, %xmm1
> > pcmpeqd %xmm0, %xmm0
> > pxor %xmm1, %xmm0
> > ```
> > 
> > is just a duplicate of `pcmpgtq %xmm1, %xmm0`?
> > 
> > Likewise for the avx/avx2 tests.
> > 
> > Know whats going on there?
> > 
> > But guess at the end of the day, this can be fixed in `LowerABD` by looking for existing dag nodes and will be probably be easier to do after this patch.
> > 
> > Maybe add a TODO in x86 `LowerABD` to fixup missed optimizations. (Likewise we always `blendv` on `cmp` result, but should be doable on the `sub`, and for avx512 should be `vpternlogd` instead of `blendv`)
> Yes, IIRC we have an existing problem with other problems with patterns using min/max pairs - we don't do enough to share SETCC nodes.
We last looked at this for rG813459ed2b0b but I wonder if really we should be doing more generically with SETCC nodes before we get this far.


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