inference: mark flag for effect-free :calls during optimization

So that they can be deleted during the first `compact!`-ion.
This allows us to delete an inlineable and effect-free, but unused call.

This is essentially an alternative of #47305, but doesn't introduce a
problem like #47374.

Author: aviatesk

base/compiler/abstractinterpretation.jl

@@ -239,6 +239,12 @@ function abstract_call_gf_by_type(interp::AbstractInterpreter, @nospecialize(f),
         # and avoid keeping track of a more complex result type.
         rettype = Any
     end
+    # mark this call statement as DCE-elgible
+    if is_removable_if_unused(all_effects)
+        add_curr_ssaflag!(sv, IR_FLAG_EFFECT_FREE)
+    else
+        sub_curr_ssaflag!(sv, IR_FLAG_EFFECT_FREE)
+    end
     add_call_backedges!(interp, rettype, all_effects, edges, matches, atype, sv)
     if !isempty(sv.pclimitations) # remove self, if present
         delete!(sv.pclimitations, sv)

base/compiler/inferencestate.jl

@@ -537,6 +537,8 @@ function print_callstack(sv::InferenceState)
 end
 
 get_curr_ssaflag(sv::InferenceState) = sv.src.ssaflags[sv.currpc]
+add_curr_ssaflag!(sv::InferenceState, flag::UInt8) = sv.src.ssaflags[sv.currpc] |= flag
+sub_curr_ssaflag!(sv::InferenceState, flag::UInt8) = sv.src.ssaflags[sv.currpc] &= ~flag
 
 function narguments(sv::InferenceState)
     def = sv.linfo.def

test/compiler/inline.jl

@@ -1077,8 +1077,7 @@ Base.setindex!(s::SafeRef, x) = setfield!(s, 1, x)
     noninlined_dce_new(s)
     nothing
 end
-# should be resolved once we merge https://github.com/JuliaLang/julia/pull/43923
-@test_broken fully_eliminated((Union{Symbol,String},)) do s
+@test fully_eliminated((Union{Symbol,String},)) do s
     noninlined_dce_new(s)
     nothing
 end
@@ -1817,6 +1816,26 @@ let ir = Base.code_ircode(big_tuple_test1, Tuple{})[1][1]
     @test length(ir.stmts) == 1
 end
 
+# inlineable but removable call should be eligible for DCE
+Base.@assume_effects :nothrow @inline function inlineable_effect_free(a::Float64)
+    a == Inf && return zero(a)
+    return sin(a) + cos(a)
+end
+@test fully_eliminated((Float64,)) do a
+    b = inlineable_effect_free(a)
+    c = b
+    nothing
+end
+
+# https://github.com/JuliaLang/julia/issues/47374
+function f47374(x)
+    [f47374(i, x) for i in 1:1]
+end
+function f47374(i::Int, x)
+    return 1.0
+end
+@test f47374(rand(1)) == Float64[1.0]
+
 # compiler should recognize effectful :static_parameter
 # https://github.com/JuliaLang/julia/issues/45490
 issue45490_1(x::Union{T, Nothing}, y::Union{T, Nothing}) where {T} = T