Split edges to have a block to add regmove & copy instructions.

When using basic block instructions cannot be added in-between jump instructions which are ending basic blocks. These changes create extra basic blocks such that extra space is available for the spilling and moving registers where they are expected.

cranelift/codegen/src/regalloc/mod.rs

@@ -10,6 +10,7 @@ pub mod register_set;
 pub mod virtregs;
 
 mod affinity;
+mod branch_splitting;
 mod coalescing;
 mod context;
 mod diversion;