Byte updates using bit fields require extension to full bytes #6448
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tautschnig
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chrisr-diffblue,
kroening and
peterschrammel
as code owners
Codecov Report
@@ Coverage Diff @@
## develop #6448 +/- ##
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- Coverage 76.02% 76.01% -0.02%
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Files 1546 1546
Lines 165352 165394 +42
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+ Hits 125711 125723 +12
- Misses 39641 39671 +30
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tautschnig
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| @@ -699,7 +700,7 @@ void goto_convertt::do_havoc_slice( | |||
| t->source_location_nonconst().set_comment( | |||
| "assertion havoc_slice " + from_expr(ns, identifier, ok_expr)); | |||
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| const array_typet array_type(char_type(), arguments[1]); | |||
| const array_typet array_type(char_type(), simplify_expr(arguments[1], ns)); | |||
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I get that this might be the right thing to do and that it fixes a bug but this doesn't immediately seem linked to the description of the PR.
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Thanks, addressed in two ways: 1) I've moved this change to a commit of its own; 2) I've added a comment explaining when a DATA_INVARIANT newly introduced here could fail (which really was what made me detect the above).
The array size may include a type cast, possibly of a constant. Therefore, the size would be found to be constant via simplification, but other ways of computing the size may fail to derive a constant.
A byte update with an update value that has a size that's not a multiple of bytes must not overwrite bits that are not in the update value. We previously generated extractbits expressions that would go out of bounds, which tripped up the SMT solvers. No longer generating these out-of-bounds expressions makes the SMT solvers happy on the Promotion3 test, which exercised this feature.
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A byte update with an update value that has a size that's not a multiple
of bytes must not overwrite bits that are not in the update value. We
previously generated extractbits expressions that would go out of
bounds, which tripped up the SMT solvers. No longer generating these
out-of-bounds expressions makes the SMT solvers happy on the Promotion3
test, which exercised this feature.