Author: Carl Friedrich Bolz <[email protected]>
Branch: regalloc-playground
Changeset: r92186:fc6b711bad77
Date: 2017-08-19 09:39 +0200
http://bitbucket.org/pypy/pypy/changeset/fc6b711bad77/
Log: improve comments
diff --git a/rpython/jit/backend/llsupport/regalloc.py
b/rpython/jit/backend/llsupport/regalloc.py
--- a/rpython/jit/backend/llsupport/regalloc.py
+++ b/rpython/jit/backend/llsupport/regalloc.py
@@ -792,23 +792,27 @@
class Lifetime(object):
def __init__(self, definition_pos, last_usage, last_real_usage=-42):
+ # all positions are indexes into the operations list
+
+ # the position where the variable is defined
self.definition_pos = definition_pos
+ # the position where the variable is last used. this includes failargs
+ # and jumps
self.last_usage = last_usage
if last_real_usage == -42:
last_real_usage = last_usage
+ # last *real* usage, ie as an argument to an operation
+ # after last_real_usage and last_usage it does not matter whether the
+ # variable is stored on the stack
self.last_real_usage = last_real_usage
def is_last_real_use_before(self, position):
return self.last_real_usage <= position
def compute_vars_longevity(inputargs, operations):
- # compute a dictionary that maps variables to index in
- # operations that is a "last-time-seen"
-
- # returns a pair longevity/useful. Non-useful variables are ones that
- # never appear in the assembler or it does not matter if they appear on
- # stack or in registers. Main example is loop arguments that go
- # only to guard operations or to jump or to finish
+ # compute a dictionary that maps variables to Lifetime information
+ # if a variable is not in the dictionary, it's operation is dead because
+ # it's side-effect-free and the result is unused
last_used = {}
last_real_usage = {}
for i in range(len(operations)-1, -1, -1):
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