[llvm] [DXIL] Implement pow lowering (PR #86733)

[Farzon Lotfi via llvm-commits]

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@@ -197,6 +198,26 @@ static bool expandLog10Intrinsic(CallInst *Orig) {
   return expandLogIntrinsic(Orig, numbers::ln2f / numbers::ln10f);
 }
 
+static bool expandPowIntrinsic(CallInst *Orig) {
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farzonl wrote:

> Or, perhaps false can be returned in certain cases, like if Orig is null or if Ty happens to be invalid.

I think for invalid cases we probably want to end execution something like `llvm_unreachable` having a return false in this case wouldn't make us handle the invalid case it would just prevent further removal of the function we are expanding. 

https://github.com/llvm/llvm-project/pull/86733