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Saving anything except a trashes a.

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This commit is contained in:
Chris Pressey 2018-04-25 13:06:11 +01:00
parent 1410989b2c
commit 80c46485f1
2 changed files with 57 additions and 7 deletions
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6
src/sixtypical/analyzer.py
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@ -777,3 +777,9 @@ class Analyzer(object):
self.analyze_block(instr.block, context)
# TODO assert no goto was encountered
context.re_introduce(baton)
if location == REG_A:
pass
else:
context.set_touched(REG_A)
context.set_unmeaningful(REG_A)

58
tests/SixtyPical Analysis.md
View File

@ -1955,17 +1955,45 @@ Basic neutral test, where the `save` makes no difference.
| }
= ok
Saving any location (other than `a`) will trash `a`.
| routine main
| inputs a, x
| outputs a, x
| trashes z, n
| {
| ld a, 1
| save x {
| ld a, 2
| }
| }
? UnmeaningfulOutputError
Saving `a` does not trash anything.
| routine main
| inputs a, x
| outputs a, x
| trashes z, n
| {
| ld x, 1
| save a {
| ld x, 2
| }
| ld x, 3
| }
= ok
A defined value that has been saved can be trashed inside the block.
It will continue to be defined outside the block.
| routine main
| inputs a
| outputs a, x
| trashes z, n
| outputs x, y
| trashes a, z, n
| {
| ld x, 0
| save x {
| ld a, 0
| ld y, 0
| trash x
| }
| }
@ -1991,14 +2019,30 @@ It will continue to be trashed outside the block.
A value which is not output from the routine, is preserved by the
routine; and can appear in a `save` exactly because a `save` preserves it.
| routine main
| outputs y
| trashes a, z, n
| {
| save x {
| ld y, 0
| ld x, 1
| }
| }
= ok
Because saving anything except `a` trashes `a`, a common idiom is to save `a`
first in a nested series of `save`s.
| routine main
| inputs a
| outputs a
| trashes z, n
| {
| save x {
| ld a, 0
| ld x, 1
| save a {
| save x {
| ld a, 0
| ld x, 1
| }
| }
| }
= ok