fallback: legalize: G_PHI <2 x s64>

Snippet:

@G.1 = external global <2 x i64>

define i32 @trunc_i17(i64 %a) {
entry:
  %A = alloca <2 x i64>, align 16
  store <2 x i64> poison, ptr %A, align 16
  %trunc = trunc i64 %a to i17
  switch i17 %trunc, label %sw.default [
    i17 1, label %sw.bb0
    i17 -1, label %sw.bb1
  ]

sw.bb0:                                           ; preds = %entry
  %LGV = load <2 x i64>, ptr @G.1, align 16
  br label %return

sw.bb1:                                           ; preds = %entry
  br label %return

sw.default:                                       ; preds = %entry
  br label %return

return:                                           ; preds = %sw.default, %sw.bb1, %sw.bb0
  %0 = phi <2 x i64> [ splat (i64 -9223372036854775808), %sw.default ], [ splat (i64 1), %sw.bb1 ], [ %LGV, %sw.bb0 ]
  %retval = phi i32 [ -1, %sw.default ], [ 0, %sw.bb0 ], [ 1, %sw.bb1 ]
  store <2 x i64> %0, ptr %A, align 16
  ret i32 %retval
}

Reproduce:

llc -O2 -mtriple=riscv64 -global-isel -global-isel-abort=2 -pass-remarks-missed=gisel.* snippet.ll -o -
llc -O2 -mtriple=riscv64 -global-isel=0 snippet.ll -o -

Local llc output:

remark: <unknown>:0:0: unable to legalize instruction: %11:_(<2 x s64>) = G_PHI %14:_(<2 x s64>), %bb.4, %16:_(<2 x s64>), %bb.3, %9:_(<2 x s64>), %bb.2 (in function: trunc_i17)
warning: Instruction selection used fallback path for trunc_i17

Occurrences (1):

Generated 2026-10-15 08:05 UTC.