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.

4 files changed, 6 insertions, 8 deletions

diff --git a/compiler/llvmGen/LlvmCodeGen.hs b/compiler/llvmGen/LlvmCodeGen.hs
index 56d8386431..21d463e5c5 100644
--- a/compiler/llvmGen/LlvmCodeGen.hs
+++ b/compiler/llvmGen/LlvmCodeGen.hs
@@ -62,7 +62,7 @@ llvmCodeGen dflags h us cmms
 -- -----------------------------------------------------------------------------
 -- | Do LLVM code generation on all these Cmms data sections.
 --
-cmmDataLlvmGens :: DynFlags -> BufHandle -> LlvmEnv -> [(Section,[CmmStatic])]
+cmmDataLlvmGens :: DynFlags -> BufHandle -> LlvmEnv -> [(Section,CmmStatics)]
                 -> [LlvmUnresData] -> IO ( LlvmEnv )
 
 cmmDataLlvmGens dflags h env [] lmdata
diff --git a/compiler/llvmGen/LlvmCodeGen/Base.hs b/compiler/llvmGen/LlvmCodeGen/Base.hs
index 59cdad4918..e73f41cde1 100644
--- a/compiler/llvmGen/LlvmCodeGen/Base.hs
+++ b/compiler/llvmGen/LlvmCodeGen/Base.hs
@@ -41,7 +41,7 @@ import Unique
 -- * Some Data Types
 --
 
-type LlvmCmmTop = GenCmmTop LlvmData [CmmStatic] (ListGraph LlvmStatement)
+type LlvmCmmTop = GenCmmTop [LlvmData] [CmmStatic] (ListGraph LlvmStatement)
 type LlvmBasicBlock = GenBasicBlock LlvmStatement
 
 -- | Unresolved code.
diff --git a/compiler/llvmGen/LlvmCodeGen/Data.hs b/compiler/llvmGen/LlvmCodeGen/Data.hs
index 3e486a544f..7cca522d39 100644
--- a/compiler/llvmGen/LlvmCodeGen/Data.hs
+++ b/compiler/llvmGen/LlvmCodeGen/Data.hs
@@ -37,8 +37,8 @@ structStr = fsLit "_struct"
 -- complete this completely though as we need to pass all CmmStatic
 -- sections before all references can be resolved. This last step is
 -- done by 'resolveLlvmData'.
-genLlvmData :: (Section, [CmmStatic]) -> LlvmUnresData
-genLlvmData (sec, CmmDataLabel lbl:xs) =
+genLlvmData :: (Section, CmmStatics) -> LlvmUnresData
+genLlvmData (sec, Statics lbl xs) =
     let static  = map genData xs
         label   = strCLabel_llvm lbl
 
@@ -50,8 +50,6 @@ genLlvmData (sec, CmmDataLabel lbl:xs) =
         alias   = LMAlias ((label `appendFS` structStr), strucTy)
     in (lbl, sec, alias, static)
 
-genLlvmData _ = panic "genLlvmData: CmmData section doesn't start with label!"
-
 
 resolveLlvmDatas ::  LlvmEnv -> [LlvmUnresData] -> [LlvmData]
                  -> (LlvmEnv, [LlvmData])
diff --git a/compiler/llvmGen/LlvmCodeGen/Ppr.hs b/compiler/llvmGen/LlvmCodeGen/Ppr.hs
index 9f25c08826..48a0d6967c 100644
--- a/compiler/llvmGen/LlvmCodeGen/Ppr.hs
+++ b/compiler/llvmGen/LlvmCodeGen/Ppr.hs
@@ -83,7 +83,7 @@ pprLlvmCmmTop _ _ (CmmData _ lmdata)
   = (vcat $ map pprLlvmData lmdata, [])
 
 pprLlvmCmmTop env count (CmmProc info lbl (ListGraph blks))
-  = let static = CmmDataLabel lbl : info
+  = let static = Statics lbl info
         (idoc, ivar) = if not (null info)
                           then pprInfoTable env count lbl static
                           else (empty, [])
@@ -103,7 +103,7 @@ pprLlvmCmmTop env count (CmmProc info lbl (ListGraph blks))
 
 
 -- | Pretty print CmmStatic
-pprInfoTable :: LlvmEnv -> Int -> CLabel -> [CmmStatic] -> (Doc, [LlvmVar])
+pprInfoTable :: LlvmEnv -> Int -> CLabel -> CmmStatics -> (Doc, [LlvmVar])
 pprInfoTable env count lbl stat
   = let unres = genLlvmData (Text, stat)
         (_, (ldata, ltypes)) = resolveLlvmData env unres