[PATCH] D78092: [GlobalISel] add legalization for G_FREEZE

[Juneyoung Lee via Phabricator via llvm-commits]

aqjune added inline comments.


================
Comment at: llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp:1772
+    Observer.changingInstr(MI);
+    widenScalarSrc(MI, WideTy, 1, TargetOpcode::G_ANYEXT);
+    widenScalarDst(MI, WideTy);
----------------
gargaroff wrote:
> arsenm wrote:
> > Is this what the DAG does? I would be slightly surprised that undef high bits would be OK
> I'm not familiar with SelectionDAG, so I might have misunderstood the extension used.
> 
> This is the code in the DAG:
> 
> ```
> SDValue DAGTypeLegalizer::PromoteIntRes_FREEZE(SDNode *N) {
>   SDValue V = GetPromotedInteger(N->getOperand(0));
>   return DAG.getNode(ISD::FREEZE, SDLoc(N),
>                      V.getValueType(), V);
> }
> ```
> 
> In the documentation of `GetPromotedInteger` it says that the upper bits contain rubbish, which suggested to me that this corresponds to `G_ANYEXT`
In case of SelDag, I think PromoteIntRes_FREEZE is correct: it is creating FREEZE instruction, so even if GetPromotedInteger returned undef bits, the result is frozen, so the high bits are frozen bits.


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  https://reviews.llvm.org/D78092/new/

https://reviews.llvm.org/D78092