[PATCH] D115629: [RISCV] Use binvi and bexti to fold and (not (srl X, C)), 1

[Jianjian Guan via Phabricator via llvm-commits]

jacquesguan added inline comments.


================
Comment at: llvm/lib/Target/RISCV/RISCVInstrInfoZb.td:795
+def : Pat<(and (not (srl GPR:$rs1, uimmlog2xlen:$shamt)), (XLenVT 1)),
+          (BEXTI (BINVI GPR:$rs1, uimmlog2xlen:$shamt),
+                 uimmlog2xlen:$shamt)>;
----------------
jacquesguan wrote:
> craig.topper wrote:
> > I wonder if the (XORI (BEXTI GPR:$rs1, $shamt), 1) we would have gotten from the original InstCombine canonicalization would be better.
> > 
> > Guess it depends on whether the Zbs instructions are implemented as well as XORI or not. There is no c.xori or that would have been a good reason to favor xori.
> Thanks, so that I could change DAGCombine to keep ` xor (and(srl X, C),1), 1`  when we have single-Bit extract instruction in backend. In this situation, at least, we fold  `(and(srl X, C),1)` into `BEXTI X, C`. What's your option about this?
Sorry, I misunderstanded your comment. Please ignore my last reply. I would simply change that pattern into 
```def : Pat<(and (not (srl GPR:$rs1, uimmlog2xlen:$shamt)), (XLenVT 1)),
                   (XORI (BEXTI GPR:$rs1, uimmlog2xlen:$shamt), (XLenVT 1)) 
```


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  https://reviews.llvm.org/D115629/new/

https://reviews.llvm.org/D115629