[llvm] [X86][SelectionDAG] - Add support for llvm.canonicalize intrinsic (PR #106370)

[Matt Arsenault via llvm-commits]

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@@ -57976,6 +57977,124 @@ static SDValue combineINTRINSIC_VOID(SDNode *N, SelectionDAG &DAG,
   return SDValue();
 }
 
+SDValue combineConstantCanonicalize(SDNode *Node, SelectionDAG &DAG) {
+  SDValue Operand = Node->getOperand(0);
+  SDLoc dl(Node);
+  EVT VT = Operand.getValueType();
+  if (ConstantFPSDNode *CFP = dyn_cast<ConstantFPSDNode>(Operand)) {
+    const APFloat &C = CFP->getValueAPF();
+    if (C.isDenormal()) {
+      DenormalMode Mode =
+          DAG.getMachineFunction().getDenormalMode(C.getSemantics());
+      assert((Mode != DenormalMode::getPositiveZero()) &&
+             "Positive denormal mode is not valid for X86 target.");
+      if (Mode == DenormalMode::getPreserveSign()) {
+        SDValue SDZero =
+            DAG.getConstantFP((C.isNegative() ? -0.0 : 0.0), dl, VT);
+        return SDZero;
+      } else if (Mode == DenormalMode::getIEEE()) {
+        return Operand;
+      }
+    } else if (C.isNaN() && C.isSignaling()) {
+      APFloat CanonicalQNaN = APFloat::getQNaN(C.getSemantics());
+      SDValue QuitNaN = DAG.getConstantFP(CanonicalQNaN, dl, VT);
+      return QuitNaN;
+    }
+  }
+  return Operand;
+}
+
+SDValue findLastStrictOpChain(SDNode *N, SelectionDAG &DAG) {
+  assert(N!=nullptr && "Trying to find last chain for a NULL Node");
+  for (unsigned i = 0, e = N->getNumOperands(); i != e; ++i) {
+    SDValue Op = N->getOperand(i);
+    if (Op.getValueType() == MVT::Other && Op.getNode()->isStrictFPOpcode())
+      return Op;
+  }
+  return DAG.getEntryNode();
+}
+
+bool isNonCanonicalizingOperation(SDNode *N) {
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arsenm wrote:

Leave optimizations for a separate patch. It's likely unsafe to do mid lowering 

https://github.com/llvm/llvm-project/pull/106370