[PATCH] D133399: [DAGCombiner] Fold (mul (sra X, BW-1), Y) -> (neg (and (sra X, BW-1), Y))

[Simon Pilgrim via Phabricator via llvm-commits]

RKSimon added inline comments.


================
Comment at: llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp:3953
+                                  SelectionDAG &DAG) {
+  if (N0.getOpcode() != ISD::SRA)
+    return SDValue();
----------------
craig.topper wrote:
> RKSimon wrote:
> > Would this work more generally if we tested for NumSignBits == BitWidth instead?
> It’s starts picking up vectors of constants if we do that and it wasn’t clear that the test changes were improvements.
> 
> I can add a TODO?
Yes a TODO would be fine


Repository:
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  https://reviews.llvm.org/D133399/new/

https://reviews.llvm.org/D133399