[PATCH] D60854: [DAGLegalize][PowerPC] Add promote legalization of addc/adde and subc/sube

[Zixuan Wu via Phabricator via llvm-commits]

wuzish added a comment.

In D60854#1472624 <https://reviews.llvm.org/D60854#1472624>, @efriedma wrote:

> Oh, I see, we start with an i32 ADDE, then https://github.com/llvm/llvm-project/blob/e7fe6dd5edb828e702d02c7cdc6565ace4c84f5b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp#L10232 narrows the operation.  We probably shouldn't perform that transform if it would produce an illegal ADDE.




>   if ((N0.getOpcode() == ISD::ADDE || N0.getOpcode() == ISD::ADDCARRY) &&
>        N0.hasOneUse() && !N0.getNode()->hasAnyUseOfValue(1) &&
>        (!LegalOperations || TLI.isOperationLegal(N0.getOpcode(), VT))) {

I think there are 2 conditions to combine as above code does. One is before operation legalization phase (!LegalOperations) and the other one is after. 
In former condition, such transformation is acceptable even operation ADDE is illegal and it only cares about type legality because illegal operation will be legalized later in DAG legalization phase (as I want to promote it). 
So the second condition does consider the legality of ADDE because it's after DAG operation legalization.


Repository:
  rL LLVM

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  https://reviews.llvm.org/D60854/new/

https://reviews.llvm.org/D60854