fallback: legalize: G_LSHR <4 x s32>

Snippet:

define <4 x i16> @test_pasubu_h(<4 x i16> %a, <4 x i16> %b) {
  %a_ext = zext <4 x i16> %a to <4 x i32>
  %b_ext = zext <4 x i16> %b to <4 x i32>
  %sub = sub <4 x i32> %a_ext, %b_ext
  %res = lshr <4 x i32> %sub, splat (i32 1)
  %res_trunc = trunc <4 x i32> %res to <4 x i16>
  ret <4 x i16> %res_trunc
}

Reproduce:

llc -mtriple=riscv64 -mattr=+experimental-p,+m,+zbb -verify-machineinstrs -global-isel -global-isel-abort=2 -pass-remarks-missed=gisel.* snippet.ll -o -
llc -mtriple=riscv64 -mattr=+experimental-p,+m,+zbb -verify-machineinstrs -global-isel=0 snippet.ll -o -

Local llc output:

remark: <unknown>:0:0: unable to legalize instruction: %7:_(<4 x s32>) = G_LSHR %4:_, %5:_(<4 x s32>) (in function: test_pasubu_h)
warning: Instruction selection used fallback path for test_pasubu_h

Occurrences (115) (first 50):

Generated 2026-10-15 08:05 UTC.