Refactoring: use a structured CmmStatics type rather than [CmmStatic]

I observed that the [CmmStatics] within CmmData uses the list in a very stylised way.
The first item in the list is almost invariably a CmmDataLabel. Many parts of the
compiler pattern match on this list and fail if this is not true.

This patch makes the invariant explicit by introducing a structured type CmmStatics
that holds the label and the list of remaining [CmmStatic].

There is one wrinkle: the x86 backend sometimes wants to output an alignment directive just
before the label. However, this can be easily fixed up by parameterising the native codegen
over the type of CmmStatics (though the GenCmmTop parameterisation) and using a pair
(Alignment, CmmStatics) there instead.

As a result, I think we will be able to remove CmmAlign and CmmDataLabel from the CmmStatic
data type, thus nuking a lot of code and failing pattern matches. This change will come as part
of my next patch.

1 files changed, 6 insertions, 6 deletions

diff --git a/compiler/nativeGen/RegAlloc/Graph/Main.hs b/compiler/nativeGen/RegAlloc/Graph/Main.hs
index cdbe98755a..298b5673d4 100644
--- a/compiler/nativeGen/RegAlloc/Graph/Main.hs
+++ b/compiler/nativeGen/RegAlloc/Graph/Main.hs
@@ -44,12 +44,12 @@ maxSpinCount	= 10
 
 -- | The top level of the graph coloring register allocator.
 regAlloc
-	:: (Outputable instr, Instruction instr)
+	:: (Outputable statics, Outputable instr, Instruction instr)
 	=> DynFlags
 	-> UniqFM (UniqSet RealReg)	-- ^ the registers we can use for allocation
 	-> UniqSet Int			-- ^ the set of available spill slots.
-	-> [LiveCmmTop instr]		-- ^ code annotated with liveness information.
-	-> UniqSM ( [NatCmmTop instr], [RegAllocStats instr] )
+	-> [LiveCmmTop statics instr]	-- ^ code annotated with liveness information.
+	-> UniqSM ( [NatCmmTop statics instr], [RegAllocStats statics instr] )
            -- ^ code with registers allocated and stats for each stage of
            -- allocation
 		
@@ -239,7 +239,7 @@ regAlloc_spin
 -- | Build a graph from the liveness and coalesce information in this code.
 buildGraph 
 	:: Instruction instr
-	=> [LiveCmmTop instr]
+	=> [LiveCmmTop statics instr]
 	-> UniqSM (Color.Graph VirtualReg RegClass RealReg)
 	
 buildGraph code
@@ -320,9 +320,9 @@ graphAddCoalesce _ _
 
 -- | Patch registers in code using the reg -> reg mapping in this graph.
 patchRegsFromGraph 
-	:: (Outputable instr, Instruction instr)
+	:: (Outputable statics, Outputable instr, Instruction instr)
 	=> Color.Graph VirtualReg RegClass RealReg
-	-> LiveCmmTop instr -> LiveCmmTop instr
+	-> LiveCmmTop statics instr -> LiveCmmTop statics instr
 
 patchRegsFromGraph graph code
  = let