Simplify backedge storage when we know we have only 1 edge

Author: serenity4

src/transform/common.jl

@@ -64,23 +64,16 @@ function ir_to_src(ir::IRCode)
 end
 
 function cache_dae_ci!(old_ci, src, debuginfo, abi, owner)
-    edges = Core.svec(old_ci)
+    mi = old_ci.def
+    edges = Core.svec(mi)
     daef_ci = CodeInstance(abi === nothing ? old_ci.def : Core.ABIOverride(abi, old_ci.def), owner, Tuple, Union{}, nothing, src, Int32(0),
         UInt(1)#=ci.min_world=#, old_ci.max_world, old_ci.ipo_purity_bits,
         nothing, debuginfo, edges)
-    add_backedges_to_callees(daef_ci, edges)
-    ccall(:jl_mi_cache_insert, Cvoid, (Any, Any), old_ci.def, daef_ci)
+    ccall(:jl_method_instance_add_backedge, Cvoid, (Any, Any, Any), mi, nothing, daef_ci)
+    ccall(:jl_mi_cache_insert, Cvoid, (Any, Any), mi, daef_ci)
     return daef_ci
 end
 
-# Equivalent to `Compiler.store_backedges` in our case, but we allow `caller.def.def` to not be a `Method`.
-function add_backedges_to_callees(caller::CodeInstance, edges::SimpleVector)
-    for edge in edges
-        isa(edge, CodeInstance) && (edge = edge.def)
-        ccall(:jl_method_instance_add_backedge, Cvoid, (Any, Any, Any), edge::MethodInstance, nothing, caller)
-    end
-end
-
 function replace_call!(ir::Union{IRCode,IncrementalCompact}, idx::SSAValue, new_call::Expr)
     @assert !isa(ir[idx][:inst], PhiNode)
     ir[idx][:inst] = new_call