[AArch64] Cannot select: t4: nxv4bf16 = fp_round t2, TargetConstant:i64<0>

[d0k]

Loop vectorizer creates these vectors if there are bf16 types in the input

target datalayout = "e-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128-Fn32"
target triple = "aarch64-unknown-linux-gnu"

define <vscale x 4 x bfloat> @Conv.9(<vscale x 4 x float> %wide.masked.load) {
  %f = fptrunc <vscale x 4 x float> %wide.masked.load to <vscale x 4 x bfloat>
  ret <vscale x 4 x bfloat> %f
}

$ llc -mtriple=aarch64-linux-gnu -mcpu=neoverse-n2 < t.ll
LLVM ERROR: Cannot select: t4: nxv4bf16 = fp_round t2, TargetConstant:i64<0>
  t2: nxv4f32,ch = CopyFromReg t0, Register:nxv4f32 %0
    t1: nxv4f32 = Register %0
  t3: i64 = TargetConstant<0>
In function: Conv.9

[llvmbot]

@llvm/issue-subscribers-backend-aarch64

Author: Benjamin Kramer (d0k)

Loop vectorizer creates these vectors if there are bf16 types in the input

target datalayout = "e-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128-Fn32"
target triple = "aarch64-unknown-linux-gnu"

define &lt;vscale x 4 x bfloat&gt; @<!-- -->Conv.9(&lt;vscale x 4 x float&gt; %wide.masked.load) {
  %f = fptrunc &lt;vscale x 4 x float&gt; %wide.masked.load to &lt;vscale x 4 x bfloat&gt;
  ret &lt;vscale x 4 x bfloat&gt; %f
}

$ llc -mtriple=aarch64-linux-gnu -mcpu=neoverse-n2 < t.ll
LLVM ERROR: Cannot select: t4: nxv4bf16 = fp_round t2, TargetConstant:i64<0>
  t2: nxv4f32,ch = CopyFromReg t0, Register:nxv4f32 %0
    t1: nxv4f32 = Register %0
  t3: i64 = TargetConstant<0>
In function: Conv.9

[c-rhodes]

reproduced on 19, fixed since 20: https://godbolt.org/z/zx9749YPd