Implement regslot inlining, document soundness concerns.

[ghc-hetmet.git] / compiler / cmm / CmmSpillReload.hs

diff --git a/compiler/cmm/CmmSpillReload.hs b/compiler/cmm/CmmSpillReload.hs
index bc7fbc3..a4bedb0 100644 (file)
--- a/compiler/cmm/CmmSpillReload.hs
+++ b/compiler/cmm/CmmSpillReload.hs
@@ -47,8 +47,15 @@ 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
 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.
+their reaching definitions, but reloads are dropped immediately after
+we return from a call and will have to be sunk by a later forward
+transformation.
+
+Note that we offer no guarantees about the consistency of the value
+in memory and the value in the register, except that they are
+equal across calls/procpoints.  If the variable is changed, this
+mapping breaks: but as the original value of the register may still
+be useful in a different context, the memory location is not updated.

 -}
 
 data DualLive = DualLive { on_stack :: RegSet, in_regs :: RegSet }
 -}
 
 data DualLive = DualLive { on_stack :: RegSet, in_regs :: RegSet }

@@ -173,9 +180,6 @@ insertSpillAndReloadRewrites graph procPoints = deepBwdRw3 first middle nothing
 
           nothing _ _ = return Nothing
 
 
           nothing _ _ = return Nothing
 

-regSlot :: LocalReg -> CmmExpr
-regSlot r = CmmStackSlot (RegSlot r) (widthInBytes $ typeWidth $ localRegType r)
-

 spill, reload :: LocalReg -> CmmNode O O
 spill  r = CmmStore  (regSlot r) (CmmReg $ CmmLocal r)
 reload r = CmmAssign (CmmLocal r) (CmmLoad (regSlot r) $ localRegType r)
 spill, reload :: LocalReg -> CmmNode O O
 spill  r = CmmStore  (regSlot r) (CmmReg $ CmmLocal r)
 reload r = CmmAssign (CmmLocal r) (CmmLoad (regSlot r) $ localRegType r)