remove unnecessary size field in BCO (#7518)

compiler/ghci/ByteCodeAsm.lhs

@@ -129,10 +129,7 @@ assembleBCO dflags (ProtoBCO nm instrs bitmap bsize arity _origin _malloced) = d
   -- pass 1: collect up the offsets of the local labels.
   let asm = mapM_ (assembleI dflags) instrs
 
-      -- Remember that the first insn starts at offset
-      --     sizeOf Word / sizeOf Word16
-      -- since offset 0 (eventually) will hold the total # of insns.
-      initial_offset = largeArg16s dflags
+      initial_offset = 0
 
       -- Jump instructions are variable-sized, there are long and short variants
       -- depending on the magnitude of the offset.  However, we can't tell what
@@ -153,8 +150,7 @@ assembleBCO dflags (ProtoBCO nm instrs bitmap bsize arity _origin _malloced) = d
         (Map.lookup lbl lbl_map)
 
   -- pass 2: run assembler and generate instructions, literals and pointers
-  let initial_insns = addListToSS emptySS $ largeArg dflags n_insns
-  let initial_state = (initial_insns, emptySS, emptySS)
+  let initial_state = (emptySS, emptySS, emptySS)
   (final_insns, final_lits, final_ptrs) <- execState initial_state $ runAsm dflags long_jumps env asm
 
   -- precomputed size should be equal to final size

rts/Interpreter.c

@@ -788,9 +788,7 @@ run_BCO:
 	register StgPtr*   ptrs       = (StgPtr*)(&bco->ptrs->payload[0]);
 #ifdef DEBUG
 	int bcoSize;
-    bcoSize = BCO_READ_NEXT_WORD;
-#else
-    BCO_NEXT_WORD;
+        bcoSize = bco->instrs->bytes / sizeof(StgWord16);
 #endif
 	IF_DEBUG(interpreter,debugBelch("bcoSize = %d\n", bcoSize));