Changes between Version 14 and Version 15 of Commentary/Compiler/NewCodeGenStupidity

Timestamp:

04/14/11 03:01:19 (2 years ago)

Author:

ezyang

Comment:

instruction reordering

Commentary/Compiler/NewCodeGenStupidity

@@ -174 +174 @@
 This pattern essentially happens for every function, since we always assign incoming parameters to temporary variables before doing anything.
 
+== Instruction reordering ==
+
+We should be able to reorder instructions in order to decrease register pressure. Here's an example from 3586.hs
+
+{{{
+        _cPY::I32 = I32[Sp - 24];
+        I32[R1 + 4] = _cPY::I32;
+        I32[R1] = stg_IND_STATIC_info;
+        I32[Sp - 8] = _cPY::I32;
+        I32[Sp - 12] = stg_upd_frame_info;
+}}}
+
+R1 and Sp probably don't clobber each other, so we ought to use _cPY twice in quick succession. Fortunately stg_IND_STATIC_info is a constant so in this case the optimization doesn't help to much, but in other cases it might make sense. TODO Find better example