Commit cb43dfcd authored by simonmar's avatar simonmar
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[project @ 2003-01-07 14:31:19 by simonmar]

Update comments
parent 6ee2bfb3
......@@ -435,17 +435,9 @@ There are four kinds of things on the stack:
- free slots (recorded in the stack free list)
- non-pointer data slots (recorded in the stack free list)
We build up a bitmap of non-pointer slots by looking down the
environment for all the non-pointer variables, and merging this with
the slots recorded in the stack free list.
There's a bit of a hack here to do with update frames: since nothing
is recorded in either the environment or the stack free list for an
update frame, the code below defaults to assuming the slots taken up
by an update frame contain pointers. Furthermore, update frames are
always in slots 0-2 at the bottom of the stack. The bitmap will
therefore end at slot 3, which is what we want (the update frame info
pointer has its own bitmap to describe the update frame).
We build up a bitmap of non-pointer slots by searching the environment
for all the pointer variables, and subtracting these from a bitmap
with initially all bits set (up to the size of the stack frame).
\begin{code}
buildLivenessMask
......
%
% (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
%
% $Id: CgMonad.lhs,v 1.36 2002/12/11 15:36:26 simonmar Exp $
% $Id: CgMonad.lhs,v 1.37 2003/01/07 14:31:20 simonmar Exp $
%
\section[CgMonad]{The code generation monad}
......@@ -206,6 +206,14 @@ type StackUsage =
Int, -- realSp: Virtual offset of real stack pointer
Int) -- hwSp: Highest value ever taken by virtSp
-- ToDo (SDM, 7 Jan 2003): I'm not sure that the distinction between
-- Free and NonPointer in the free list is needed any more. It used
-- to be needed because we constructed bitmaps from the free list, but
-- now we construct bitmaps by finding all the live pointer bindings
-- instead. Non-pointer stack slots (i.e. saved cost centres) can
-- just be removed from the free list instead of being recorded as a
-- NonPointer.
type HeapUsage =
(HeapOffset, -- virtHp: Virtual offset of highest-allocated word
HeapOffset) -- realHp: Virtual offset of real heap ptr
......
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