9.21.6.1 Branch Improvement

Certain pseudo opcodes are permitted for branch instructions. They expand to the shortest branch instruction that reach the target. Generally these mnemonics are made by prepending j to the start of Motorola mnemonic. These pseudo opcodes are not affected by the --short-branches or --force-long-branches options.

The following table summarizes the pseudo-operations.

                             Displacement Width
          +-------------------------------------------------------------+
       |                  Options                              |
       | --short-branches           --force-long-branches      |
          +--------------------------+----------------------------------+
       Op |BYTE             WORD  | BYTE          WORD            |
          +--------------------------+----------------------------------+
      bsr | bsr <pc-rel>    <error> |            jsr <abs>       |
      bra | bra <pc-rel>    <error> |            jmp <abs>       |
     jbsr | bsr <pc-rel>   jsr <abs> | bsr <pc-rel>  jsr <abs>       |
     jbra | bra <pc-rel>   jmp <abs> | bra <pc-rel>  jmp <abs>       |
      bXX | bXX <pc-rel>    <error> |            bNX +3; jmp <abs> |
     jbXX | bXX <pc-rel>   bNX +3; | bXX <pc-rel>  bNX +3; jmp <abs> |
       |             jmp <abs> |                            |
          +--------------------------+----------------------------------+
     XX: condition
     NX: negative of condition XX
     

jbsr

jbra

These are the simplest jump pseudo-operations; they always map to one particular machine instruction, depending on the displacement to the branch target.

jb XX

Here, jb XX stands for an entire family of pseudo-operations, where XX is a conditional branch or condition-code test. The full list of pseudo-ops in this family is:

           jbcc   jbeq   jbge   jbgt   jbhi   jbvs   jbpl  jblo
           jbcs   jbne   jblt   jble   jbls   jbvc   jbmi
     

For the cases of non-PC relative displacements and long displacements, as issues a longer code fragment in terms of NX, the opposite condition to XX. For example, for the non-PC relative case:

              jbXX foo
     

gives

               bNXs oof
               jmp foo
           oof:
     

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