fallback: legalize: G_LSHR <2 x s64>

Snippet:

define <2 x i32> @test_pasubu_w(<2 x i32> %a, <2 x i32> %b) {
  %a_ext = zext <2 x i32> %a to <2 x i64>
  %b_ext = zext <2 x i32> %b to <2 x i64>
  %sub = sub <2 x i64> %a_ext, %b_ext
  %res = lshr <2 x i64> %sub, splat (i64 1)
  %res_trunc = trunc <2 x i64> %res to <2 x i32>
  ret <2 x i32> %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:_(<2 x s64>) = G_LSHR %4:_, %5:_(<2 x s64>) (in function: test_pasubu_w)
warning: Instruction selection used fallback path for test_pasubu_w

Occurrences (188) (first 50):

Generated 2026-10-15 08:05 UTC.