Fix use counts for mutable struct SROA

base/compiler/ssair/passes.jl

@@ -688,10 +688,14 @@ function getfield_elim_pass!(ir::IRCode, domtree::DomTree)
         compact[idx] = val === nothing ? nothing : val.x
     end
 
-    # Copy the use count, `finish` may modify it and for our predicate
-    # below we need it consistent with the state of the IR here.
+
+    non_dce_finish!(compact)
+    # Copy the use count, `simple_dce!` may modify it and for our predicate
+    # below we need it consistent with the state of the IR here (after tracking
+    # phi node arguments, but before dce).
     used_ssas = copy(compact.used_ssas)
-    ir = finish(compact)
+    simple_dce!(compact)
+    ir = complete(compact)
     # Now go through any mutable structs and see which ones we can eliminate
     for (idx, (intermediaries, defuse)) in defuses
         intermediaries = collect(intermediaries)

test/compiler/irpasses.jl

@@ -37,3 +37,29 @@ let m = Meta.@lower 1 + 1
     Core.Compiler.verify_ir(ir)
     @test isa(ir.stmts[3], Core.PhiNode) && length(ir.stmts[3].edges) == 1
 end
+
+# Tests for SROA
+
+mutable struct Foo30594; x::Float64; end
+Base.copy(x::Foo30594) = Foo30594(x.x)
+function add!(p::Foo30594, off::Foo30594)
+    p.x += off.x
+    return p
+end
+Base.:(+)(a::Foo30594, b::Foo30594) = add!(copy(a), b)
+
+let results = Float64[]
+    @noinline use30594(x) = push!(results, x.x); nothing
+    function foo30594(cnt::Int, dx::Int)
+        step = Foo30594(dx)
+        curr = step + Foo30594(1)
+        for i in 1:cnt
+            use30594(curr)
+            curr = curr + step
+        end
+        nothing
+    end
+
+    foo30594(4, -1)
+    @test results == [0.0, -1.0, -2.0, -3.0]
+end