Comments only

2 files changed, 35 insertions, 14 deletions

diff --git a/compiler/cmm/CmmSpillReload.hs b/compiler/cmm/CmmSpillReload.hs
index 1cdafa9baa..df05a654f8 100644
--- a/compiler/cmm/CmmSpillReload.hs
+++ b/compiler/cmm/CmmSpillReload.hs
@@ -31,20 +31,23 @@ import UniqSet
 import Data.Maybe
 import Prelude hiding (zip)
 
--- The point of this module is to insert spills and reloads to
--- establish the invariant that at a call (or at any proc point with
--- an established protocol) all live variables not expected in
--- registers are sitting on the stack.  We use a backward analysis to
--- insert spills and reloads.  It should be followed by a
--- forward transformation to sink reloads as deeply as possible, so as
--- to reduce register pressure.
-
--- A variable can be expected to be live in a register, live on the
--- stack, or both.  This analysis ensures that spills and reloads are
--- inserted as needed to make sure that every live variable needed
--- after a call is available on the stack.  Spills are pushed back to
--- their reaching definitions, but reloads are dropped wherever needed
--- and will have to be sunk by a later forward transformation.
+{- Note [Overview of spill/reload]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+The point of this module is to insert spills and reloads to
+establish the invariant that at a call (or at any proc point with
+an established protocol) all live variables not expected in
+registers are sitting on the stack.  We use a backward analysis to
+insert spills and reloads.  It should be followed by a
+forward transformation to sink reloads as deeply as possible, so as
+to reduce register pressure.
+
+A variable can be expected to be live in a register, live on the
+stack, or both.  This analysis ensures that spills and reloads are
+inserted as needed to make sure that every live variable needed
+after a call is available on the stack.  Spills are pushed back to
+their reaching definitions, but reloads are dropped wherever needed
+and will have to be sunk by a later forward transformation.
+-}
 
 data DualLive = DualLive { on_stack :: RegSet, in_regs :: RegSet }
 
diff --git a/compiler/cmm/cmm-notes b/compiler/cmm/cmm-notes
index 2fab86fd6d..823fd0ae5e 100644
--- a/compiler/cmm/cmm-notes
+++ b/compiler/cmm/cmm-notes
@@ -2,6 +2,24 @@ Notes on new codegen (Sept 09)
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

 

 Things to do:

+

+ - CmmContFlowOpt.runCmmContFlowOptZs is not called!

+ - Why is runCmmOpts called from HscMain?  Seems too "high up".

+   In fact HscMain calls (runCmmOpts cmmCfgOptsZ) which is what

+   runCmmContFlowOptZs does.  Tidy up!

+

+

+ - AsmCodeGen has a generic Cmm optimiser; move this into new pipeline

+

+ - AsmCodeGen has post-native-cg branch elimiator (shortCutBranches);

+   we ultimately want to share this with the Cmm branch eliminator.

+

+ - At the moment, references to global registers like Hp are "lowered" 

+   late (in AsmCodeGen.fixAssignTop and cmmToCmm). We should do this

+   early, in the new native codegen, much in the way that we lower 

+   calling conventions.  Might need to be a bit sophisticated about

+   aliasing.

+

  - Refactor Cmm so that it contains only shared stuff

    Add a module MoribundCmm which contains stuff from

    Cmm for old code gen path