irinterp: Don't try to rekill fall-through terminators (#49815)

If a fall-through terminator was already Bottom, we should not attempt
to rekill the successor edge, because it was already deleted.
Yet another fix in the #49692, #49750, #49797 series, which is
turning out to be quite a rabit hole. Also fix a typo in the
verifer tweak where we were looking at the BB idx rather than
the terminator idx.

Author: Keno

base/compiler/ssair/irinterp.jl

@@ -247,13 +247,17 @@ function _ir_abstract_constant_propagation(interp::AbstractInterpreter, irsv::IR
                 any_refined = true
                 delete!(ssa_refined, idx)
             end
+            is_terminator_or_phi = isa(inst, PhiNode) || isa(inst, GotoNode) || isa(inst, GotoIfNot) || isa(inst, ReturnNode) || isexpr(inst, :enter)
+            if typ === Bottom && (idx != lstmt || !is_terminator_or_phi)
+                continue
+            end
             if any_refined && reprocess_instruction!(interp,
                     idx, bb, inst, typ, irsv, extra_reprocess)
                 push!(ssa_refined, idx)
                 inst = ir.stmts[idx][:inst]
                 typ = ir.stmts[idx][:type]
             end
-            if typ === Bottom && !(isa(inst, PhiNode) || isa(inst, GotoNode) || isa(inst, GotoIfNot) || isa(inst, ReturnNode) || isexpr(inst, :enter))
+            if typ === Bottom && !is_terminator_or_phi
                 kill_terminator_edges!(irsv, lstmt, bb)
                 if idx != lstmt
                     for idx2 in (idx+1:lstmt-1)

base/compiler/ssair/verify.jl

@@ -174,12 +174,14 @@ function verify_ir(ir::IRCode, print::Bool=true,
                     end
                     isa(stmt, PhiNode) || break
                 end
-                if isempty(block.succs) && ir.stmts[idx][:type] == Union{}
+                termidx = last(block.stmts)
+                stmttyp = ir.stmts[termidx][:type]
+                if isempty(block.succs) && stmttyp == Union{}
                     # Allow fallthrough terminators that are known to error to
                     # be removed from the CFG. Ideally we'd add an unreachable
                     # here, but that isn't always possible.
                 else
-                    @verify_error "Block $idx successors ($(block.succs)), does not match fall-through terminator ($terminator)"
+                    @verify_error "Block $idx successors ($(block.succs)), does not match fall-through terminator %$termidx ($terminator)::$stmttyp"
                     error("")
                 end
             end