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

[Damyan Pepper 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) {
+
+  Value *X = Orig->getOperand(0);
+  Value *Y = Orig->getOperand(1);
+  Type *Ty = X->getType();
+  IRBuilder<> Builder(Orig->getParent());
+  Builder.SetInsertPoint(Orig);
+
+  auto *Log2Call =
+      Builder.CreateIntrinsic(Ty, Intrinsic::log2, {X}, nullptr, "elt.log2");
+  auto *Mul = Builder.CreateFMul(Log2Call, Y);
+  auto *Exp2Call =
+      Builder.CreateIntrinsic(Ty, Intrinsic::exp2, {Mul}, nullptr, "elt.exp2");
+  Exp2Call->setTailCall(Orig->isTailCall());
+  Exp2Call->setAttributes(Orig->getAttributes());
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damyanp wrote:

I don't know...it's the sort of thing that looks like it's important and worth doing, but what do I know?!  If you can't think of a way to write a test that observes whether or not these have been copied properly then maybe it shouldn't be there.  Maybe this is something we should deal with in a follow-up issue, since it sounds like it is more widespread than just the code touched in this PR.

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