+data JumpDest = DestBlockId BlockId | DestImm Imm
+
+canShortcut :: Instr -> Maybe JumpDest
+#if i386_TARGET_ARCH || x86_64_TARGET_ARCH
+canShortcut (JXX ALWAYS id) = Just (DestBlockId id)
+canShortcut (JMP (OpImm imm)) = Just (DestImm imm)
+#endif
+canShortcut _ = Nothing
+
+shortcutJump :: (BlockId -> Maybe JumpDest) -> Instr -> Instr
+#if i386_TARGET_ARCH || x86_64_TARGET_ARCH
+shortcutJump fn insn@(JXX cc id) =
+ case fn id of
+ Nothing -> insn
+ Just (DestBlockId id') -> shortcutJump fn (JXX cc id')
+ Just (DestImm imm) -> shortcutJump fn (JXX_GBL cc imm)
+#endif
+shortcutJump fn other = other
+
+-- Here because it knows about JumpDest
+shortcutStatic :: (BlockId -> Maybe JumpDest) -> CmmStatic -> CmmStatic
+shortcutStatic fn (CmmStaticLit (CmmLabel lab))
+ | Just uq <- maybeAsmTemp lab
+ = CmmStaticLit (CmmLabel (shortBlockId fn (BlockId uq)))
+shortcutStatic fn (CmmStaticLit (CmmLabelDiffOff lbl1 lbl2 off))
+ | Just uq <- maybeAsmTemp lbl1
+ = CmmStaticLit (CmmLabelDiffOff (shortBlockId fn (BlockId uq)) lbl2 off)
+ -- slightly dodgy, we're ignoring the second label, but this
+ -- works with the way we use CmmLabelDiffOff for jump tables now.
+shortcutStatic fn other_static
+ = other_static
+
+shortBlockId fn blockid@(BlockId uq) =
+ case fn blockid of
+ Nothing -> mkAsmTempLabel uq
+ Just (DestBlockId blockid') -> shortBlockId fn blockid'
+ Just (DestImm (ImmCLbl lbl)) -> lbl
+ _other -> panic "shortBlockId"
+