fallback: legalize: G_INSERT_SUBVECTOR <8 x s8>,<4 x s8>

Snippet:

define <8 x i8> @insert_zero_v4i8(<4 x i8> %v) {
  %r = call <8 x i8> @llvm.vector.insert.v8i8.v4i8(<8 x i8> zeroinitializer, <4 x i8> %v, i64 0)
  ret <8 x i8> %r
}

; Function Attrs: nocallback nofree nosync nounwind speculatable willreturn memory(none)
declare <8 x i8> @llvm.vector.insert.v8i8.v4i8(<8 x i8>, <4 x i8>, i64 immarg) #0

attributes #0 = { nocallback nofree nosync nounwind speculatable willreturn memory(none) }

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: %3:_(<8 x s8>) = G_INSERT_SUBVECTOR %4:_, %0:_(<4 x s8>), 0 (in function: insert_zero_v4i8)
warning: Instruction selection used fallback path for insert_zero_v4i8

Occurrences (3):

Generated 2026-10-15 08:05 UTC.