Remove OldCmm, convert backends to consume new Cmm

This removes the OldCmm data type and the CmmCvt pass that converts
new Cmm to OldCmm.  The backends (NCGs, LLVM and C) have all been
converted to consume new Cmm.

The main difference between the two data types is that conditional
branches in new Cmm have both true/false successors, whereas in OldCmm
the false case was a fallthrough.  To generate slightly better code we
occasionally need to invert a conditional to ensure that the
branch-not-taken becomes a fallthrough; this was previously done in
CmmCvt, and it is now done in CmmContFlowOpt.

We could go further and use the Hoopl Block representation for native
code, which would mean that we could use Hoopl's postorderDfs and
analyses for native code, but for now I've left it as is, using the
old ListGraph representation for native code.

1 files changed, 8 insertions, 7 deletions

diff --git a/compiler/nativeGen/RegAlloc/Linear/Main.hs b/compiler/nativeGen/RegAlloc/Linear/Main.hs
index fc5b992603..fa71457808 100644
--- a/compiler/nativeGen/RegAlloc/Linear/Main.hs
+++ b/compiler/nativeGen/RegAlloc/Linear/Main.hs
@@ -116,7 +116,7 @@ import Instruction
 import Reg
 
 import BlockId
-import OldCmm hiding (RegSet)
+import Cmm hiding (RegSet)
 
 import Digraph
 import DynFlags
@@ -743,12 +743,13 @@ allocateRegsAndSpill reading keep spills alloc (r:rs)
                 Just (InMem slot) | reading   -> doSpill (ReadMem slot)
                                   | otherwise -> doSpill WriteMem
                 Nothing | reading   ->
-                   -- pprPanic "allocateRegsAndSpill: Cannot read from uninitialized register" (ppr r)
-                   -- ToDo: This case should be a panic, but we
-                   -- sometimes see an unreachable basic block which
-                   -- triggers this because the register allocator
-                   -- will start with an empty assignment.
-                   doSpill WriteNew
+                   pprPanic "allocateRegsAndSpill: Cannot read from uninitialized register" (ppr r)
+                   -- NOTE: if the input to the NCG contains some
+                   -- unreachable blocks with junk code, this panic
+                   -- might be triggered.  Make sure you only feed
+                   -- sensible code into the NCG.  In CmmPipeline we
+                   -- call removeUnreachableBlocks at the end for this
+                   -- reason.
 
                         | otherwise -> doSpill WriteNew