[RISCV] Custom legalize vXbf16 BUILD_VECTOR without Zfbfmin.

By default, type legalization will try to promote the build_vector,
but that generic type legalizer doesn't support that. Bitcast to
vXi16 instead. Same as what we do for vXf16 without Zfhmin.

Fixes llvm#100846.

llvm/lib/Target/RISCV/RISCVISelLowering.cpp

@@ -1285,8 +1285,14 @@ RISCVTargetLowering::RISCVTargetLowering(const TargetMachine &TM,
 
         if (VT.getVectorElementType() == MVT::bf16) {
           setOperationAction({ISD::VP_FP_ROUND, ISD::VP_FP_EXTEND}, VT, Custom);
-          // FIXME: We should prefer BUILD_VECTOR over SPLAT_VECTOR.
-          setOperationAction(ISD::SPLAT_VECTOR, VT, Custom);
+          if (Subtarget.hasStdExtZfbfmin()) {
+            // FIXME: We should prefer BUILD_VECTOR over SPLAT_VECTOR.
+            setOperationAction(ISD::SPLAT_VECTOR, VT, Custom);
+          } else {
+            // We need to custom legalize bf16 build vectors if Zfbfmin isn't
+            // available.
+            setOperationAction(ISD::BUILD_VECTOR, MVT::bf16, Custom);
+          }
           setOperationAction(
               {ISD::VP_MERGE, ISD::VP_SELECT, ISD::VSELECT, ISD::SELECT}, VT,
               Custom);
@@ -3935,9 +3941,9 @@ static SDValue lowerBUILD_VECTOR(SDValue Op, SelectionDAG &DAG,
   MVT VT = Op.getSimpleValueType();
   assert(VT.isFixedLengthVector() && "Unexpected vector!");
 
-  // If we don't have scalar f16, we need to bitcast to an i16 vector.
-  if (VT.getVectorElementType() == MVT::f16 &&
-      !Subtarget.hasStdExtZfhmin())
+  // If we don't have scalar f16/bf16, we need to bitcast to an i16 vector.
+  if ((VT.getVectorElementType() == MVT::f16 && !Subtarget.hasStdExtZfhmin()) ||
+      (VT.getVectorElementType() == MVT::bf16 && !Subtarget.hasStdExtZfbfmin()))
     return lowerBUILD_VECTORvXf16(Op, DAG);
 
   if (ISD::isBuildVectorOfConstantSDNodes(Op.getNode()) ||

llvm/test/CodeGen/RISCV/rvv/fixed-vectors-fp-splat-bf16.ll

@@ -0,0 +1,111 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc -mtriple=riscv32 -target-abi=ilp32d -mattr=+v,+zfbfmin,+zvfbfmin -verify-machineinstrs < %s | FileCheck %s --check-prefixes=ZFBFMIN-ZVFBFMIN
+; RUN: llc -mtriple=riscv32 -target-abi=ilp32d -mattr=+v,+zvfbfmin -verify-machineinstrs < %s | FileCheck %s --check-prefixes=ZVFBFMIN
+; RUN: llc -mtriple=riscv64 -target-abi=lp64d -mattr=+v,+zfbfmin,+zvfbfmin -verify-machineinstrs < %s | FileCheck %s --check-prefixes=ZFBFMIN-ZVFBFMIN
+; RUN: llc -mtriple=riscv64 -target-abi=lp64d -mattr=+v,+zvfbfmin -verify-machineinstrs < %s | FileCheck %s --check-prefixes=ZVFBFMIN
+
+define <8 x bfloat> @splat_v8bf16(ptr %x, bfloat %y) {
+; ZFBFMIN-ZVFBFMIN-LABEL: splat_v8bf16:
+; ZFBFMIN-ZVFBFMIN:       # %bb.0:
+; ZFBFMIN-ZVFBFMIN-NEXT:    fcvt.s.bf16 fa5, fa0
+; ZFBFMIN-ZVFBFMIN-NEXT:    vsetvli a0, zero, e32, m2, ta, ma
+; ZFBFMIN-ZVFBFMIN-NEXT:    vfmv.v.f v10, fa5
+; ZFBFMIN-ZVFBFMIN-NEXT:    vsetvli zero, zero, e16, m1, ta, ma
+; ZFBFMIN-ZVFBFMIN-NEXT:    vfncvtbf16.f.f.w v8, v10
+; ZFBFMIN-ZVFBFMIN-NEXT:    ret
+;
+; ZVFBFMIN-LABEL: splat_v8bf16:
+; ZVFBFMIN:       # %bb.0:
+; ZVFBFMIN-NEXT:    fmv.x.w a0, fa0
+; ZVFBFMIN-NEXT:    vsetivli zero, 8, e16, m1, ta, ma
+; ZVFBFMIN-NEXT:    vmv.v.x v8, a0
+; ZVFBFMIN-NEXT:    ret
+  %a = insertelement <8 x bfloat> poison, bfloat %y, i32 0
+  %b = shufflevector <8 x bfloat> %a, <8 x bfloat> poison, <8 x i32> zeroinitializer
+  ret <8 x bfloat> %b
+}
+
+define <16 x bfloat> @splat_16bf16(ptr %x, bfloat %y) {
+; ZFBFMIN-ZVFBFMIN-LABEL: splat_16bf16:
+; ZFBFMIN-ZVFBFMIN:       # %bb.0:
+; ZFBFMIN-ZVFBFMIN-NEXT:    fcvt.s.bf16 fa5, fa0
+; ZFBFMIN-ZVFBFMIN-NEXT:    vsetvli a0, zero, e32, m4, ta, ma
+; ZFBFMIN-ZVFBFMIN-NEXT:    vfmv.v.f v12, fa5
+; ZFBFMIN-ZVFBFMIN-NEXT:    vsetvli zero, zero, e16, m2, ta, ma
+; ZFBFMIN-ZVFBFMIN-NEXT:    vfncvtbf16.f.f.w v8, v12
+; ZFBFMIN-ZVFBFMIN-NEXT:    ret
+;
+; ZVFBFMIN-LABEL: splat_16bf16:
+; ZVFBFMIN:       # %bb.0:
+; ZVFBFMIN-NEXT:    fmv.x.w a0, fa0
+; ZVFBFMIN-NEXT:    vsetivli zero, 16, e16, m2, ta, ma
+; ZVFBFMIN-NEXT:    vmv.v.x v8, a0
+; ZVFBFMIN-NEXT:    ret
+  %a = insertelement <16 x bfloat> poison, bfloat %y, i32 0
+  %b = shufflevector <16 x bfloat> %a, <16 x bfloat> poison, <16 x i32> zeroinitializer
+  ret <16 x bfloat> %b
+}
+
+define <8 x bfloat> @splat_zero_v8bf16(ptr %x) {
+; ZFBFMIN-ZVFBFMIN-LABEL: splat_zero_v8bf16:
+; ZFBFMIN-ZVFBFMIN:       # %bb.0:
+; ZFBFMIN-ZVFBFMIN-NEXT:    vsetvli a0, zero, e16, m1, ta, ma
+; ZFBFMIN-ZVFBFMIN-NEXT:    vmv.v.i v8, 0
+; ZFBFMIN-ZVFBFMIN-NEXT:    ret
+;
+; ZVFBFMIN-LABEL: splat_zero_v8bf16:
+; ZVFBFMIN:       # %bb.0:
+; ZVFBFMIN-NEXT:    vsetivli zero, 8, e16, m1, ta, ma
+; ZVFBFMIN-NEXT:    vmv.v.i v8, 0
+; ZVFBFMIN-NEXT:    ret
+  ret <8 x bfloat> splat (bfloat 0.0)
+}
+
+define <16 x bfloat> @splat_zero_16bf16(ptr %x) {
+; ZFBFMIN-ZVFBFMIN-LABEL: splat_zero_16bf16:
+; ZFBFMIN-ZVFBFMIN:       # %bb.0:
+; ZFBFMIN-ZVFBFMIN-NEXT:    vsetvli a0, zero, e16, m2, ta, ma
+; ZFBFMIN-ZVFBFMIN-NEXT:    vmv.v.i v8, 0
+; ZFBFMIN-ZVFBFMIN-NEXT:    ret
+;
+; ZVFBFMIN-LABEL: splat_zero_16bf16:
+; ZVFBFMIN:       # %bb.0:
+; ZVFBFMIN-NEXT:    vsetivli zero, 16, e16, m2, ta, ma
+; ZVFBFMIN-NEXT:    vmv.v.i v8, 0
+; ZVFBFMIN-NEXT:    ret
+  ret <16 x bfloat> splat (bfloat 0.0)
+}
+
+define <8 x bfloat> @splat_negzero_v8bf16(ptr %x) {
+; ZFBFMIN-ZVFBFMIN-LABEL: splat_negzero_v8bf16:
+; ZFBFMIN-ZVFBFMIN:       # %bb.0:
+; ZFBFMIN-ZVFBFMIN-NEXT:    lui a0, 1048568
+; ZFBFMIN-ZVFBFMIN-NEXT:    vsetvli a1, zero, e16, m1, ta, ma
+; ZFBFMIN-ZVFBFMIN-NEXT:    vmv.v.x v8, a0
+; ZFBFMIN-ZVFBFMIN-NEXT:    ret
+;
+; ZVFBFMIN-LABEL: splat_negzero_v8bf16:
+; ZVFBFMIN:       # %bb.0:
+; ZVFBFMIN-NEXT:    lui a0, 1048568
+; ZVFBFMIN-NEXT:    vsetivli zero, 8, e16, m1, ta, ma
+; ZVFBFMIN-NEXT:    vmv.v.x v8, a0
+; ZVFBFMIN-NEXT:    ret
+  ret <8 x bfloat> splat (bfloat -0.0)
+}
+
+define <16 x bfloat> @splat_negzero_16bf16(ptr %x) {
+; ZFBFMIN-ZVFBFMIN-LABEL: splat_negzero_16bf16:
+; ZFBFMIN-ZVFBFMIN:       # %bb.0:
+; ZFBFMIN-ZVFBFMIN-NEXT:    lui a0, 1048568
+; ZFBFMIN-ZVFBFMIN-NEXT:    vsetvli a1, zero, e16, m2, ta, ma
+; ZFBFMIN-ZVFBFMIN-NEXT:    vmv.v.x v8, a0
+; ZFBFMIN-ZVFBFMIN-NEXT:    ret
+;
+; ZVFBFMIN-LABEL: splat_negzero_16bf16:
+; ZVFBFMIN:       # %bb.0:
+; ZVFBFMIN-NEXT:    lui a0, 1048568
+; ZVFBFMIN-NEXT:    vsetivli zero, 16, e16, m2, ta, ma
+; ZVFBFMIN-NEXT:    vmv.v.x v8, a0
+; ZVFBFMIN-NEXT:    ret
+  ret <16 x bfloat> splat (bfloat -0.0)
+}