[llvm] [X86][FP16] Widen 128/256-bit CVTTP2xI to 512-bit when VLX not enabled (PR #142763)

[Simon Pilgrim via llvm-commits]

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@@ -21612,22 +21616,39 @@ SDValue X86TargetLowering::LowerFP_TO_INT(SDValue Op, SelectionDAG &DAG) const {
     }
 
     if (Subtarget.hasFP16() && SrcVT.getVectorElementType() == MVT::f16) {
-      if (VT == MVT::v8i16 || VT == MVT::v16i16 || VT == MVT::v32i16)
+      if ((HasVLX && (VT == MVT::v8i16 || VT == MVT::v16i16)) ||
+          VT == MVT::v32i16)
         return Op;
 
       MVT ResVT = VT;
       MVT EleVT = VT.getVectorElementType();
       if (EleVT != MVT::i64)
         ResVT = EleVT == MVT::i32 ? MVT::v4i32 : MVT::v8i16;
 
-      if (SrcVT != MVT::v8f16) {
+      if (SrcVT == MVT::v2f16 || SrcVT == MVT::v4f16) {
         SDValue Tmp =
             IsStrict ? DAG.getConstantFP(0.0, dl, SrcVT) : DAG.getUNDEF(SrcVT);
         SmallVector<SDValue, 4> Ops(SrcVT == MVT::v2f16 ? 4 : 2, Tmp);
         Ops[0] = Src;
         Src = DAG.getNode(ISD::CONCAT_VECTORS, dl, MVT::v8f16, Ops);
       }
 
+      if (!HasVLX) {
+        assert(Subtarget.useAVX512Regs() && "Unexpected features!");
+        // Widen to 512-bits.
+        unsigned IntSize = EleVT.getSizeInBits();
+        unsigned Num = IntSize > 16 ? 512 / IntSize : 32;
+        MVT TmpVT = MVT::getVectorVT(MVT::f16, Num);
+        ResVT = MVT::getVectorVT(EleVT, Num);
+        // Need to concat with zero vector for strict fp to avoid spurious
+        // exceptions.
+        // TODO: Should we just do this for non-strict as well?
+        SDValue Tmp =
+            IsStrict ? DAG.getConstantFP(0.0, dl, TmpVT) : DAG.getUNDEF(TmpVT);
+        Src = DAG.getNode(ISD::INSERT_SUBVECTOR, dl, TmpVT, Tmp, Src,
+                          DAG.getVectorIdxConstant(0, dl));
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RKSimon wrote:

use widenSubVector ?

https://github.com/llvm/llvm-project/pull/142763