Update TODO.md

TODO.md

@@ -1,4 +1,3 @@
-
 ## Instructions
 
 ```
@@ -36,11 +35,38 @@ twi
 
 ## Codegen
 
+### Tracing
+
+Tracing modes:
+- off (0)
+- syscalls (1)
+- fn calls (2)
+- all instructions (3)
+
+Inject extern functions into module:
+- XeTraceKernelCall(caller_ia, cia, name, state)
+- XeTraceUserCall(caller_ia, cia, name, state)
+- XeTraceInstruction(cia, name, state)
+
+### Calling convention
+
+Experiment with fastcc? May need typedef fn ptrs to call into the JITted code.
+
 ### Indirect branches (ctr/lr)
 
 emit_control.cc XeEmitBranchTo
 Need to take the value in LR/CTR and do something with it.
 
+Return path:
+- In SDB see if the function follows the 'return' semantic:
+  - mfspr LR / mtspr LR/CTR / bcctr -- at end?
+- In codegen add a BB that is just return.
+- If a block 'returns', branch to the return BB.
+
+Tail calls:
+- If in a call BB check next BB.
+- If next is a return, optimize to a tail call.
+
 Fast path:
 - Every time LR would be stashed, add the value of LR (some NIA) to a lookup
   table.