inlining: relax finalizer inlining control-flow restriction

Eager `finalizer` inlining (#45272) currently has a restriction that
requires all the def/uses are in a same basic block.

This commit relaxes that restriction a bit by allowing def/uses to
involve control flow when all of them are dominated by a `finalizer`
call to be inlined, since in that case it is safe to insert the body of
`finalizer` at the end of all the def/uses, e.g.
```julia
Base.@assume_effects :nothrow safeprint(@nospecialize x...) = print(x...)
@noinline nothrow_side_effect(x) =
    Base.@assume_effects :total !:effect_free @CCall jl_(x::Any)::Cvoid
mutable struct DoAllocWithFieldInter
    x
end
function register_finalizer!(obj::DoAllocWithFieldInter)
    finalizer(obj) do this
        nothrow_side_effect(nothing)
    end
end

let src = code_typed1() do
        for i = -1000:1000
            o = DoAllocWithFieldInter(i)
            register_finalizer!(o)
            if i == 1000
                safeprint(o.x, '\n')
            elseif i > 0
                safeprint(o.x)
            end
        end
    end
    # the finalzier call gets inlined
    @test count(isinvoke(:nothrow_side_effect), src.code) == 1
end
```

There is a room for further improvement though -- if we have a way to
compute the post-domination, we can also inline a `finalizer` call
in a case when a `finalizer` block is post-dominated by all the def/uses
e.g.
```
let src = code_typed1() do
        for i = -1000:1000
            o = DoAllocWithFieldInter(i)
            if i == 1000
                safeprint(o.x, '\n')
            elseif i > 0
                safeprint(o.x)
            end
            register_finalizer!(o)
        end
    end
    # currently this is broken
    @test_broken count(isinvoke(:nothrow_side_effect), src.code) == 1
end
```

base/compiler/ssair/passes.jl

@@ -1098,34 +1098,44 @@ function try_inline_finalizer!(ir::IRCode, argexprs::Vector{Any}, idx::Int, mi::
     return true
 end
 
-is_nothrow(ir::IRCode, pc::Int) = ir.stmts[pc][:flag] & (IR_FLAG_EFFECT_FREE | IR_FLAG_NOTHROW) ≠ 0
+is_nothrow(ir::IRCode, pc::Int) = ir.stmts[pc][:flag] & (IR_FLAG_NOTHROW | IR_FLAG_EFFECT_FREE) ≠ 0
 
-function try_resolve_finalizer!(ir::IRCode, idx::Int, finalizer_idx::Int, defuse::SSADefUse, inlining::InliningState)
-    # For now: Require that all uses and defs are in the same basic block,
-    # so that live range calculations are easy.
-    bb = ir.cfg.blocks[block_for_inst(ir.cfg, first(defuse.uses).idx)]
+function try_resolve_finalizer!(ir::IRCode, idx::Int, finalizer_idx::Int, defuse::SSADefUse, inlining::InliningState, lazydomtree::LazyDomtree)
+    # For now: Require that all the uses and defs are dominated by `finalizer` block
+    # TODO: further relax this restriction by allowing a case when `finalizer` block is post-dominated by them
     minval::Int = typemax(Int)
     maxval::Int = 0
-
-    function check_in_range(x::Union{Int,SSAUse})
-        if isa(x, SSAUse)
-            didx = x.idx
+    function update_idx!(duidx::Int)
+        if duidx < minval
+            minval = duidx
+        end
+        if duidx > maxval
+            maxval = duidx
+        end
+    end
+
+    domtree = get!(lazydomtree)
+    finalizer_bb = block_for_inst(ir, finalizer_idx)
+    update_idx!(finalizer_idx)
+    alloc_bb = block_for_inst(ir, idx)
+    dominates(domtree, alloc_bb, finalizer_bb) || return nothing
+    update_idx!(idx)
+    function check_defuse(x::Union{Int,SSAUse})
+        duidx = x isa SSAUse ? x.idx : x
+        duidx == finalizer_idx && return true
+        bb = block_for_inst(ir, duidx)
+        if dominates(domtree, finalizer_bb, bb)
+            update_idx!(duidx)
+            return true
+        # TODO elseif post_dominates(domtree, bb, finalizer_bb)
+        #     update_idx!(duidx)
+        #     return true
         else
-            didx = x
-        end
-        didx in bb.stmts || return false
-        if didx < minval
-            minval = didx
+            return false
         end
-        if didx > maxval
-            maxval = didx
-        end
-        return true
     end
-
-    check_in_range(idx) || return nothing
-    all(check_in_range, defuse.uses) || return nothing
-    all(check_in_range, defuse.defs) || return nothing
+    all(check_defuse, defuse.uses) || return nothing
+    all(check_defuse, defuse.defs) || return nothing
 
     # For now: Require all statements in the basic block range to be nothrow.
     all(minval:maxval) do idx::Int
@@ -1184,7 +1194,7 @@ function sroa_mutables!(ir::IRCode, defuses::IdDict{Int, Tuple{SPCSet, SSADefUse
             end
         end
         if finalizer_idx !== nothing && inlining !== nothing
-            try_resolve_finalizer!(ir, idx, finalizer_idx, defuse, inlining)
+            try_resolve_finalizer!(ir, idx, finalizer_idx, defuse, inlining, lazydomtree)
             continue
         end
         # Partition defuses by field

test/compiler/inline.jl

@@ -1184,7 +1184,7 @@ end
 
 # Test that we can inline a finalizer for a struct that does not otherwise escape
 @noinline nothrow_side_effect(x) =
-    @Base.assume_effects :total !:effect_free @ccall jl_(x::Any)::Cvoid
+    Base.@assume_effects :total !:effect_free @ccall jl_(x::Any)::Cvoid
 
 mutable struct DoAllocNoEscape
     function DoAllocNoEscape()
@@ -1344,6 +1344,91 @@ let src = code_typed1() do
     @test !any(isinvoke(:finalizer), src.code)
 end
 
+# tests finalizer inlining when def/uses involve control flow
+Base.@assume_effects :nothrow safeprint(@nospecialize x...) = print(x...)
+mutable struct DoAllocWithField
+    x
+    function DoAllocWithField(x)
+        finalizer(new(x)) do this
+            nothrow_side_effect(nothing)
+        end
+    end
+end
+mutable struct DoAllocWithFieldInter
+    x
+end
+function register_finalizer!(obj::DoAllocWithFieldInter)
+    finalizer(obj) do this
+        nothrow_side_effect(nothing)
+    end
+end
+let src = code_typed1() do
+        for i = -1000:1000
+            o = DoAllocWithField(i)
+            if i == 1000
+                safeprint(o.x, '\n')
+            elseif i > 0
+                safeprint(o.x)
+            end
+        end
+    end
+    @test count(isinvoke(:nothrow_side_effect), src.code) == 1
+end
+let src = code_typed1() do
+        for i = -1000:1000
+            o = DoAllocWithField(0)
+            o.x = i # with `setfield!`
+            if i == 1000
+                safeprint(o.x, '\n')
+            elseif i > 0
+                safeprint(o.x)
+            end
+        end
+    end
+    @test count(isinvoke(:nothrow_side_effect), src.code) == 1
+end
+let src = code_typed1() do
+        for i = -1000:1000
+            o = DoAllocWithFieldInter(i)
+            register_finalizer!(o)
+            if i == 1000
+                safeprint(o.x, '\n')
+            elseif i > 0
+                safeprint(o.x)
+            end
+        end
+    end
+    @test count(isinvoke(:nothrow_side_effect), src.code) == 1
+end
+let src = code_typed1() do
+        for i = -1000:1000
+            o = DoAllocWithFieldInter(0)
+            o.x = i # with `setfield!``
+            register_finalizer!(o)
+            if i == 1000
+                safeprint(o.x, '\n')
+            elseif i > 0
+                safeprint(o.x)
+            end
+        end
+    end
+    @test count(isinvoke(:nothrow_side_effect), src.code) == 1
+end
+let src = code_typed1() do
+        for i = -1000:1000
+            o = DoAllocWithFieldInter(i)
+            if i == 1000
+                safeprint(o.x, '\n')
+            elseif i > 0
+                safeprint(o.x)
+            end
+            register_finalizer!(o)
+        end
+    end
+    # TODO we can fix this case by checking a case when a finalizer block is post-dominated by all the def/uses
+    @test_broken count(isinvoke(:nothrow_side_effect), src.code) == 1
+end
+
 # optimize `[push!|pushfirst!](::Vector{Any}, x...)`
 @testset "optimize `$f(::Vector{Any}, x...)`" for f = Any[push!, pushfirst!]
     @eval begin

test/compiler/irutils.jl

@@ -17,7 +17,12 @@ function iscall((src, f)::Tuple{IR,Base.Callable}, @nospecialize(x)) where IR<:U
         singleton_type(argextype(x, src)) === f
     end
 end
-iscall(pred::Base.Callable, @nospecialize(x)) = isexpr(x, :call) && pred(x.args[1])
+function iscall(pred::Base.Callable, @nospecialize(x))
+    if isexpr(x, :(=))
+        x = x.args[2]
+    end
+    isexpr(x, :call) && pred(x.args[1])
+end
 
 # check if `x` is a statically-resolved call of a function whose name is `sym`
 isinvoke(y) = @nospecialize(x) -> isinvoke(y, x)