Code-size optimisation for top-level indirections (#7308)

Top-level indirections are often generated when there is a cast, e.g.

foo :: T
foo = bar `cast` (some coercion)

For these we were generating a full-blown CAF, which is a fair chunk
of code.

This patch makes these indirections generate a single IND_STATIC
closure (4 words) instead.  This is exactly what the CAF would
evaluate to eventually anyway, we're just shortcutting the whole
process.

1 files changed, 8 insertions, 0 deletions

diff --git a/compiler/codeGen/StgCmmClosure.hs b/compiler/codeGen/StgCmmClosure.hs
index e4c42d203d..7f44f67ff7 100644
--- a/compiler/codeGen/StgCmmClosure.hs
+++ b/compiler/codeGen/StgCmmClosure.hs
@@ -63,6 +63,7 @@ module StgCmmClosure (
         -- * InfoTables
         mkDataConInfoTable,
         cafBlackHoleInfoTable,
+        indStaticInfoTable,
         staticClosureNeedsLink,
     ) where
 
@@ -915,6 +916,13 @@ cafBlackHoleInfoTable
                  , cit_prof = NoProfilingInfo
                  , cit_srt  = NoC_SRT }
 
+indStaticInfoTable :: CmmInfoTable
+indStaticInfoTable
+  = CmmInfoTable { cit_lbl  = mkIndStaticInfoLabel
+                 , cit_rep  = indStaticRep
+                 , cit_prof = NoProfilingInfo
+                 , cit_srt  = NoC_SRT }
+
 staticClosureNeedsLink :: Bool -> CmmInfoTable -> Bool
 -- A static closure needs a link field to aid the GC when traversing
 -- the static closure graph.  But it only needs such a field if either