[llvm] AMDGPU: Libcall expand fast pow/powr/pown/rootn for float case (PR #180553)

[Matt Arsenault via llvm-commits]

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@@ -1170,6 +1198,260 @@ bool AMDGPULibCalls::fold_rootn(FPMathOperator *FPOp, IRBuilder<> &B,
   return false;
 }
 
+// is_integer(y) => trunc(y) == y
+static Value *emitIsInteger(IRBuilder<> &B, Value *Y) {
+  Value *TruncY = B.CreateUnaryIntrinsic(Intrinsic::trunc, Y);
+  return B.CreateFCmpOEQ(TruncY, Y);
+}
+
+static Value *emitIsEvenInteger(IRBuilder<> &B, Value *Y) {
+  // Even integers are still integers after division by 2.
+  auto *HalfY = B.CreateFMul(Y, ConstantFP::get(Y->getType(), 0.5));
+  return emitIsInteger(B, HalfY);
+}
+
+// is_odd_integer(y) => is_integer(y) && !is_even_integer(y)
+static Value *emitIsOddInteger(IRBuilder<> &B, Value *Y) {
+  Value *IsIntY = emitIsInteger(B, Y);
+  Value *IsEvenY = emitIsEvenInteger(B, Y);
+  Value *NotEvenY = B.CreateNot(IsEvenY);
+  return B.CreateAnd(IsIntY, NotEvenY);
+}
----------------
arsenm wrote:

The fmul is preferable to the integer operations. All of these alternatives have much worse codegen and break value tracking. I'm actually trying to eliminate all bithacking on FP operations in all library functions. 

https://github.com/llvm/llvm-project/pull/180553