Constant-folding: don't pass through GHC's Int/Word (fix #11704)

Constant-folding rules for integerToWord/integerToInt were performing
the following coercions at compilation time:

    integerToWord: target's Integer -> ghc's Word -> target's Word
    integerToInt : target's Integer -> ghc's Int -> target's Int

1) It was wrong for cross-compilers when GHC's word size is smaller than
   the target one. This patch avoids passing through GHC's word-sized
   types:

    integerToWord: target's Integer -> ghc's Integer -> target's Word
    integerToInt : target's Integer -> ghc's Integer -> target's Int

2) Additionally we didn't wrap the target word/int literal to make it
   fit into the target's range! This broke the invariant of literals
   only containing values in range.

   The existing code is wrong only with a 64-bit cross-compiling GHC,
   targeting a 32-bit platform, and performing constant folding on a
   literal that doesn't fit in a 32-bit word. If GHC was built with
   DEBUG, the assertion in GHC.Types.Literal.mkLitWord would fail.
   Otherwise the bad transformation would go unnoticed.

1 files changed, 1 insertions, 1 deletions

diff --git a/compiler/GHC/HsToCore/Foreign/Decl.hs b/compiler/GHC/HsToCore/Foreign/Decl.hs
index 4d6abc4132..e50db56eec 100644
--- a/compiler/GHC/HsToCore/Foreign/Decl.hs
+++ b/compiler/GHC/HsToCore/Foreign/Decl.hs
@@ -453,7 +453,7 @@ dsFExportDynamic id co0 cconv = do
           to be entered using an external calling convention
           (stdcall, ccall).
          -}
-        adj_args      = [ mkIntLitInt platform (ccallConvToInt cconv)
+        adj_args      = [ mkIntLit platform (fromIntegral (ccallConvToInt cconv))
                         , Var stbl_value
                         , Lit (LitLabel fe_nm mb_sz_args IsFunction)
                         , Lit (mkLitString typestring)