bpo-43760: Check for tracing using 'bitwise or' instead of branch in dispatch.

[markshannon]

About 1% faster

Use bitwise or instead of additional jump to handle tracing in dispatch.

What was:

if (use_tracing) goto tracing_dispatchgoto*jump_table[opcode];

becomes:

 goto *jump_table[opcode | use_tracing];

use_tracing is now either 0 or 255

Special opcode 255 (DO_TRACING) handles tracing and then jumps to the original instruction.

The main complexity comes from needing access to the last instruction when tracing. This means that we update frame->f_lasti and next_instr at the start of the instruction, instead of at the end of the previous instruction.

https://bugs.python.org/issue43760

[bedevere-bot]

🤖 New build scheduled with the buildbot fleet by @markshannon for commit a9ff904 🤖

If you want to schedule another build, you need to add the ":hammer: test-with-buildbots" label again.

[markshannon]

Buildbot failures seem unrelated: A network error and too many open files.