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, 2 insertions, 4 deletions

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])