optimizer: eliminate more isdefined checks

Follows up #44708 -- in that PR I missed the most obvious optimization
opportunity, i.e. we can safely eliminate `isdefined` checks when all
fields are defined at allocation site.
This change allows us to eliminate capturing closure constructions when
the body and callsite of capture closure is available within a optimized
frame, e.g.:
```julia
function abmult(r::Int, x0)
    if r < 0
        r = -r
    end
    f = x -> x * r
    return @inline f(x0)
end
```
```diff
diff --git a/_master.jl b/_pr.jl
index ea06d865b75..c38f221090f 100644
--- a/_master.jl
+++ b/_pr.jl
@@ -1,24 +1,19 @@
 julia> @code_typed abmult(-3, 3)
 CodeInfo(
-1 ── %1  = Core.Box::Type{Core.Box}
-│    %2  = %new(%1, r@_2)::Core.Box
-│    %3  = Core.isdefined(%2, :contents)::Bool
-└───       goto #3 if not %3
+1 ──       goto #3 if not true
 2 ──       goto #4
 3 ──       $(Expr(:throw_undef_if_not, :r, false))::Any
-4 ┄─ %7  = (r@_2 < 0)::Any
-└───       goto #9 if not %7
-5 ── %9  = Core.isdefined(%2, :contents)::Bool
-└───       goto #7 if not %9
+4 ┄─ %4  = (r@_2 < 0)::Any
+└───       goto #9 if not %4
+5 ──       goto #7 if not true
 6 ──       goto #8
 7 ──       $(Expr(:throw_undef_if_not, :r, false))::Any
-8 ┄─ %13 = -r@_2::Any
-9 ┄─ %14 = φ (#4 => r@_2, #8 => %13)::Any
-│    %15 = Core.isdefined(%2, :contents)::Bool
-└───       goto #11 if not %15
+8 ┄─ %9  = -r@_2::Any
+9 ┄─ %10 = φ (#4 => r@_2, #8 => %9)::Any
+└───       goto #11 if not true
 10 ─       goto #12
 11 ─       $(Expr(:throw_undef_if_not, :r, false))::Any
-12 ┄ %19 = (x0 * %14)::Any
+12 ┄ %14 = (x0 * %10)::Any
 └───       goto #13
-13 ─       return %19
+13 ─       return %14
 ) => Any
```

base/compiler/ssair/passes.jl

@@ -372,10 +372,7 @@ function lift_leaves(compact::IncrementalCompact,
  lift_arg!(compact, leaf, cache_key, def, 1+field, lifted_leaves)
  continue
  elseif isexpr(def, :new)
- typ = widenconst(types(compact)[leaf])
- if isa(typ, UnionAll)
- typ = unwrap_unionall(typ)
- end
+ typ = unwrap_unionall(widenconst(types(compact)[leaf]))
  (isa(typ, DataType) && !isabstracttype(typ)) || return nothing
  @assert !ismutabletype(typ)
  if length(def.args) < 1+field
@@ -786,10 +783,7 @@ function sroa_pass!(ir::IRCode)
  push!(preserved, preserved_arg.id)
  continue
  elseif isexpr(def, :new)
- typ = widenconst(argextype(SSAValue(defidx), compact))
- if isa(typ, UnionAll)
- typ = unwrap_unionall(typ)
- end
+ typ = unwrap_unionall(widenconst(argextype(SSAValue(defidx), compact)))
  if typ isa DataType && !ismutabletype(typ)
  record_immutable_preserve!(new_preserves, def, compact)
  push!(preserved, preserved_arg.id)
@@ -948,10 +942,7 @@ function sroa_mutables!(ir::IRCode, defuses::IdDict{Int, Tuple{SPCSet, SSADefUse
  defexpr = ir[SSAValue(idx)][:inst]
  isexpr(defexpr, :new) || continue
  newidx = idx
- typ = ir.stmts[newidx][:type]
- if isa(typ, UnionAll)
- typ = unwrap_unionall(typ)
- end
+ typ = unwrap_unionall(ir.stmts[newidx][:type])
  # Could still end up here if we tried to setfield! on an immutable, which would
  # error at runtime, but is not illegal to have in the IR.
  ismutabletype(typ) || continue
@@ -1023,6 +1014,13 @@ function sroa_mutables!(ir::IRCode, defuses::IdDict{Int, Tuple{SPCSet, SSADefUse
  end
  has_safe_def(ir, get_domtree(), allblocks, du, newidx, use.idx) || @goto skip
  end
+ else # always have some definition at the allocation site
+ for i = 1:length(du.uses)
+ use = du.uses[i]
+ if use.kind === :isdefined
+ ir[SSAValue(use.idx)][:inst] = true
+ end
+ end
  end
  end
  # Everything accounted for. Go field by field and perform idf:

test/compiler/irpasses.jl

@@ -493,6 +493,31 @@ let src = code_typed1(isdefined_elim)
 end
 @test isdefined_elim() == Any[]
 
+function abmult(r::Int, x0)
+ if r < 0
+ r = -r
+ end
+ f = x -> x * r
+ return @inline f(x0)
+end
+let src = code_typed1(abmult, (Int,Int))
+ @test is_scalar_replaced(src)
+end
+@test abmult(-3, 3) == 9
+
+function abmult2(r0::Int, x0)
+ r::Int = r0
+ if r < 0
+ r = -r
+ end
+ f = x -> x * r
+ return f(x0)
+end
+let src = code_typed1(abmult2, (Int,Int))
+ @test is_scalar_replaced(src)
+end
+@test abmult2(-3, 3) == 9
+
 # comparison lifting
 # ==================