optimize: Delete incoming unreachable edges from PhiNode

base/compiler/optimize.jl

@@ -1104,6 +1104,20 @@ function convert_to_ircode(ci::CodeInfo, sv::OptimizationState)
                         code[i] = nothing
                     end
                 end
+            elseif isa(expr, PhiNode)
+                new_edges = Int32[]
+                new_vals = Any[]
+                for j = 1:length(expr.edges)
+                    edge = expr.edges[j]
+                    (edge in sv.unreachable || (ssavaluetypes[edge] === Union{} && !isa(code[edge], PhiNode))) && continue
+                    push!(new_edges, edge)
+                    if isassigned(expr.values, j)
+                        push!(new_vals, expr.values[j])
+                    else
+                        resize!(new_vals, length(new_edges))
+                    end
+                end
+                code[i] = PhiNode(new_edges, new_vals)
             end
         end
     end

test/compiler/ssair.jl

@@ -9,16 +9,6 @@ include("irutils.jl")
 
 make_bb(preds, succs) = BasicBlock(Compiler.StmtRange(0, 0), preds, succs)
 
-function make_ci(code)
-    ci = (Meta.@lower 1 + 1).args[1]
-    ci.code = code
-    nstmts = length(ci.code)
-    ci.ssavaluetypes = nstmts
-    ci.codelocs = fill(Int32(1), nstmts)
-    ci.ssaflags = fill(Int32(0), nstmts)
-    return ci
-end
-
 # TODO: this test is broken
 #let code = Any[
 #        GotoIfNot(SlotNumber(2), 4),
@@ -763,3 +753,75 @@ end
         end
     end
 end
+
+# Test that things don't break if one branch of the frontend PhiNode becomes unreachable
+const global_error_switch_const1::Bool = false
+function gen_unreachable_phinode_edge1(world::UInt, source, args...)
+    ci = make_codeinfo(Any[
+        # block 1
+        GlobalRef(@__MODULE__, :global_error_switch_const1),
+        GotoIfNot(SSAValue(1), 4),
+        # block 2
+        Expr(:call, identity, Argument(3)),
+        # block 3
+        PhiNode(Int32[2, 3], Any[Argument(2), SSAValue(3)]),
+        ReturnNode(SSAValue(4))
+    ]; slottypes=Any[Any,Int,Int])
+    ci.slotnames = Symbol[:var"#self#", :x, :y]
+    return ci
+end
+@eval function f_unreachable_phinode_edge1(x, y)
+    $(Expr(:meta, :generated, gen_unreachable_phinode_edge1))
+    $(Expr(:meta, :generated_only))
+    #= no body =#
+end
+@test f_unreachable_phinode_edge1(1, 2) == 1
+
+const global_error_switch_const2::Bool = true
+function gen_unreachable_phinode_edge2(world::UInt, source, args...)
+    ci = make_codeinfo(Any[
+        # block 1
+        GlobalRef(@__MODULE__, :global_error_switch_const2),
+        GotoIfNot(SSAValue(1), 4),
+        # block 2
+        Expr(:call, identity, Argument(3)),
+        # block 3
+        PhiNode(Int32[2, 3], Any[Argument(2), SSAValue(3)]),
+        ReturnNode(SSAValue(4))
+    ]; slottypes=Any[Any,Int,Int])
+    ci.slotnames = Symbol[:var"#self#", :x, :y]
+    return ci
+end
+@eval function f_unreachable_phinode_edge2(x, y)
+    $(Expr(:meta, :generated, gen_unreachable_phinode_edge2))
+    $(Expr(:meta, :generated_only))
+    #= no body =#
+end
+@test f_unreachable_phinode_edge2(1, 2) == 2
+
+global global_error_switch::Bool = true
+function gen_must_throw_phinode_edge(world::UInt, source, _)
+    ci = make_codeinfo(Any[
+        # block 1
+        GlobalRef(@__MODULE__, :global_error_switch),
+        GotoIfNot(SSAValue(1), 4),
+        # block 2
+        Expr(:call, error, "This error is expected"),
+        # block 3
+        PhiNode(Int32[2, 3], Any[1, 2]),
+        ReturnNode(SSAValue(4))
+    ]; slottypes=Any[Any])
+    ci.slotnames = Symbol[:var"#self#"]
+    return ci
+end
+@eval function f_must_throw_phinode_edge()
+    $(Expr(:meta, :generated, gen_must_throw_phinode_edge))
+    $(Expr(:meta, :generated_only))
+    #= no body =#
+end
+let ir = first(only(Base.code_ircode(f_must_throw_phinode_edge)))
+    @test !any(@nospecialize(x)->isa(x,PhiNode), ir.stmts.stmt)
+end
+@test_throws ErrorException f_must_throw_phinode_edge()
+global global_error_switch = false
+@test f_must_throw_phinode_edge() == 1