[X86][BF16] Customize INSERT_VECTOR_ELT for bf16 when feature BF16 is on

Fixes root cause of #63017.
The reason is similar to BUILD_VECTOR. We have legal vector type but
still soft promote for scalar type. So we need to customize these scalar
to vector nodes.

Reviewed By: RKSimon

Differential Revision: https://reviews.llvm.org/D155961

llvm/lib/Target/X86/X86ISelLowering.cpp

@@ -2276,9 +2276,10 @@ X86TargetLowering::X86TargetLowering(const X86TargetMachine &TM,
     addRegisterClass(MVT::v8bf16, &X86::VR128XRegClass);
     addRegisterClass(MVT::v16bf16, &X86::VR256XRegClass);
     // We set the type action of bf16 to TypeSoftPromoteHalf, but we don't
-    // provide the method to promote BUILD_VECTOR. Set the operation action
-    // Custom to do the customization later.
+    // provide the method to promote BUILD_VECTOR and INSERT_VECTOR_ELT.
+    // Set the operation action Custom to do the customization later.
     setOperationAction(ISD::BUILD_VECTOR, MVT::bf16, Custom);
+    setOperationAction(ISD::INSERT_VECTOR_ELT, MVT::bf16, Custom);
     for (auto VT : {MVT::v8bf16, MVT::v16bf16}) {
       setF16Action(VT, Expand);
       setOperationAction(ISD::FADD, VT, Expand);
@@ -20751,6 +20752,14 @@ SDValue X86TargetLowering::LowerINSERT_VECTOR_ELT(SDValue Op,
   SDValue N2 = Op.getOperand(2);
   auto *N2C = dyn_cast<ConstantSDNode>(N2);
 
+  if (EltVT == MVT::bf16) {
+    MVT IVT = VT.changeVectorElementTypeToInteger();
+    SDValue Res = DAG.getNode(ISD::INSERT_VECTOR_ELT, dl, IVT,
+                              DAG.getBitcast(IVT, N0),
+                              DAG.getBitcast(MVT::i16, N1), N2);
+    return DAG.getBitcast(VT, Res);
+  }
+
   if (!N2C) {
     // Variable insertion indices, usually we're better off spilling to stack,
     // but AVX512 can use a variable compare+select by comparing against all

llvm/test/CodeGen/X86/bfloat.ll

@@ -1158,4 +1158,29 @@ define <32 x bfloat> @pr63017_2() nounwind {
   ret <32 x bfloat> %1
 }
 
+define <32 x bfloat> @pr62997_3(<32 x bfloat> %0, bfloat %1) {
+; SSE2-LABEL: pr62997_3:
+; SSE2:       # %bb.0:
+; SSE2-NEXT:    movq %xmm0, %rax
+; SSE2-NEXT:    movabsq $-4294967296, %rcx # imm = 0xFFFFFFFF00000000
+; SSE2-NEXT:    andq %rax, %rcx
+; SSE2-NEXT:    movzwl %ax, %eax
+; SSE2-NEXT:    movd %xmm4, %edx
+; SSE2-NEXT:    shll $16, %edx
+; SSE2-NEXT:    orl %eax, %edx
+; SSE2-NEXT:    orq %rcx, %rdx
+; SSE2-NEXT:    movq %rdx, %xmm4
+; SSE2-NEXT:    movsd {{.*#+}} xmm0 = xmm4[0],xmm0[1]
+; SSE2-NEXT:    retq
+;
+; BF16-LABEL: pr62997_3:
+; BF16:       # %bb.0:
+; BF16-NEXT:    vmovd %xmm1, %eax
+; BF16-NEXT:    vpinsrw $1, %eax, %xmm0, %xmm1
+; BF16-NEXT:    vinserti32x4 $0, %xmm1, %zmm0, %zmm0
+; BF16-NEXT:    retq
+  %3 = insertelement <32 x bfloat> %0, bfloat %1, i64 1
+  ret <32 x bfloat> %3
+}
+
 declare <32 x bfloat> @llvm.masked.load.v32bf16.p0(ptr, i32, <32 x i1>, <32 x bfloat>)