py/emit: Suppress unreachable bytecode/native code that follows jump.

This new logic tracks when an unconditional jump/raise occurs in the
emitted code stream (bytecode or native machine code) and suppresses all
subsequent code, until a label is assigned.  This eliminates a lot of
cases of dead code, with relatively simple logic.

This commit combined with the previous one (that removed the existing
dead-code finding logic) has the following code size change:

       bare-arm:   -16 -0.028%
    minimal x86:   -60 -0.036%
       unix x64:  -368 -0.070%
    unix nanbox:   -80 -0.017%
          stm32:  -204 -0.052% PYBV10
         cc3200:    +0 +0.000%
        esp8266:  -232 -0.033% GENERIC
          esp32:  -224 -0.015% GENERIC[incl -40(data)]
         mimxrt:  -192 -0.054% TEENSY40
     renesas-ra:  -200 -0.032% RA6M2_EK
            nrf:   +28 +0.015% pca10040
            rp2:  -256 -0.050% PICO
           samd:   -12 -0.009% ADAFRUIT_ITSYBITSY_M4_EXPRESS

Signed-off-by: Damien George <damien@micropython.org>

1 files changed, 4 insertions, 4 deletions

diff --git a/tests/cmdline/cmd_showbc.py b/tests/cmdline/cmd_showbc.py
index e5874f990..4a2e6500a 100644
--- a/tests/cmdline/cmd_showbc.py
+++ b/tests/cmdline/cmd_showbc.py
@@ -119,12 +119,12 @@ def f():
     #from sys import * # tested at module scope
 
     # raise
-    raise
-    raise 1
+    if a: raise
+    if a: raise 1
 
     # return
-    return
-    return 1
+    if a: return
+    if a: return 1
 
 # function with lots of locals
 def f():