[RISCV] Cannot select nxv2bf16 = RISCVISD::VFSLIDE1UP_VL

[topperc]

This test case give a cannot select error with -mattr=+zfbfmin,+zvfbfmin,+zvl64b

define <2 x bfloat> @vslide1up_2xbfloat(<2 x bfloat> %v, bfloat %b) {
  %vb = insertelement <2 x bfloat> poison, bfloat %b, i64 0
  %v1 = shufflevector <2 x bfloat> %v, <2 x bfloat> %vb, <2 x i32> <i32 2, i32 0
  ret <2 x bfloat> %v1
}

We need to disable lowerVECTOR_SHUFFLEAsVSlide1 for bf16. We probably also need to disable it for f16 without Zfh.

CC: @lukel97 @preames

[llvmbot]

@llvm/issue-subscribers-backend-risc-v

Author: Craig Topper (topperc)

This test case give a cannot select error with -mattr=+zfbfmin,+zvfbfmin,+zvl64b

define &lt;2 x bfloat&gt; @<!-- -->vslide1up_2xbfloat(&lt;2 x bfloat&gt; %v, bfloat %b) {
  %vb = insertelement &lt;2 x bfloat&gt; poison, bfloat %b, i64 0
  %v1 = shufflevector &lt;2 x bfloat&gt; %v, &lt;2 x bfloat&gt; %vb, &lt;2 x i32&gt; &lt;i32 2, i32 0
  ret &lt;2 x bfloat&gt; %v1
}

We need to disable lowerVECTOR_SHUFFLEAsVSlide1 for bf16. We probably also need to disable it for f16 without Zfh.

CC: @lukel97 @preames

[lukel97]

Is there a reason why we couldn't lower this as a fmv.x.w and vslide1up.vx?

[topperc]

Is there a reason why we couldn't lower this as a fmv.x.w and vslide1up.vx?

That would work too.