cfg_simplify: Fix bug in my bugfix (#52337)

The fix in #52323 was not quite correct. Fix that and adjust the test to
more accurately reflect the actual issue.

Author: Keno

base/compiler/ssair/passes.jl

@@ -2336,9 +2336,9 @@ function cfg_simplify!(ir::IRCode)
                             end
                         elseif new_edge == -1
                             @assert length(phi.edges) == 1
-                            if isassigned(phi.values, old_index)
+                            if isassigned(renamed_values, old_index)
                                 push!(edges, -1)
-                                push!(values, phi.values[old_index])
+                                push!(values, renamed_values[old_index])
                             end
                         elseif new_edge == -3
                             # Multiple predecessors, we need to expand out this phi

test/compiler/irpasses.jl

@@ -1576,17 +1576,21 @@ end
 # Test CFG simplify with single predecessor phi node
 let code = Any[
         # Block 1
-        Expr(:call, Base.inferencebarrier, 1),
         GotoNode(3),
         # Block 2
-        PhiNode(Int32[1], Any[SSAValue(1)]),
-        ReturnNode(SSAValue(3))
+        nothing,
+        # Block 3
+        Expr(:call, Base.inferencebarrier, 1),
+        GotoNode(5),
+        # Block 4
+        PhiNode(Int32[4], Any[SSAValue(3)]),
+        ReturnNode(SSAValue(5))
     ]
     ir = make_ircode(code)
     ir = Core.Compiler.cfg_simplify!(ir)
     Core.Compiler.verify_ir(ir)
-    @test length(ir.cfg.blocks) == 1
+    @test length(ir.cfg.blocks) <= 2
     ir = Core.Compiler.compact!(ir)
-    @test length(ir.stmts) == 2
-    @test (ir[SSAValue(2)][:stmt]::ReturnNode).val == SSAValue(1)
+    @test length(ir.stmts) <= 3
+    @test (ir[SSAValue(length(ir.stmts))][:stmt]::ReturnNode).val !== nothing
 end