fallback: legalize: G_ASHR <2 x s64>

Snippet:

define <2 x i32> @test_paadd_w(<2 x i32> %a, <2 x i32> %b) {
  %ext.a = sext <2 x i32> %a to <2 x i64>
  %ext.b = sext <2 x i32> %b to <2 x i64>
  %add = add nsw <2 x i64> %ext.a, %ext.b
  %shift = ashr <2 x i64> %add, splat (i64 1)
  %res = trunc <2 x i64> %shift to <2 x i32>
  ret <2 x i32> %res
}

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_ASHR %4:_, %5:_(<2 x s64>) (in function: test_paadd_w)
warning: Instruction selection used fallback path for test_paadd_w

Occurrences (120) (first 50):

Generated 2026-10-15 08:05 UTC.