[llvm] [X86] Use an FP-based expansion for v4i32 ctlz on SSE2-only targets (PR #167034)

[Matt Arsenault via llvm-commits]

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@@ -9480,6 +9480,53 @@ SDValue TargetLowering::expandVPCTLZ(SDNode *Node, SelectionDAG &DAG) const {
   return DAG.getNode(ISD::VP_CTPOP, dl, VT, Op, Mask, VL);
 }
 
+
+SDValue TargetLowering::expandCTLZWithFP(SDNode *Node, SelectionDAG &DAG) const {
+  SDLoc dl(Node);
+  SDValue Op = Node->getOperand(0);
+  EVT VT = Op.getValueType();
+
+  assert(VT.isVector() && "This expansion is intended for vectors");
+
+  EVT EltVT = VT.getVectorElementType();
+  EVT FloatVT, CmpVT;
+  unsigned BitWidth, MantissaBits, ExponentBias;
+
+  // Converting to float type
+  if (EltVT == MVT::i32) {
+    FloatVT = VT.changeVectorElementType(MVT::f32);
+    BitWidth = 32;
+    MantissaBits = 23;
+    ExponentBias = 127;
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arsenm wrote:

Should get these from the fltSemantics instead of hardcoding it 

https://github.com/llvm/llvm-project/pull/167034