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Aug 21, 2018
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Add overview of constant propagator #2778

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7 changes: 5 additions & 2 deletions src/analyses/README.md
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Expand Up @@ -30,9 +30,12 @@ To be documented.

To be documented.

\subsection analyses-constant-propagation Constant propagation (constant_propagator_ait)
\subsection analyses-constant-propagation Constant propagation (\ref constant_propagator_ait)

To be documented.
A simple, unsound constant propagator. Replaces RHS symbol expressions (variable
reads) with their values when they appear to have a unique value at a particular
program point. Unsound with respect to pointer operations on the left-hand side
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Is that genuinely the case? It's probably unsound for concurrent code, but I'm not sure about pointers.

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Yes: https://github.com/diffblue/cbmc/blob/develop/src/analyses/constant_propagator.cpp#L38 (assign with anything but a symbol on the LHS is a no-op)

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Ouch. I wasn't quite aware how incomplete it was.

of assignments.

\subsection analyses-taint Taint analysis (custom_bitvector_analysist)

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10 changes: 10 additions & 0 deletions src/analyses/constant_propagator.h
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Expand Up @@ -8,6 +8,16 @@ Author: Peter Schrammel

/// \file
/// Constant propagation
///
/// A simple, unsound constant propagator. Assignments to symbols (local and
/// global variables) are tracked, and propagated if a unique value is found
/// at a given use site. Function calls are accounted for (they are assumed to
/// overwrite all address-taken variables; see \ref dirtyt), but assignments
/// through pointers are not (they are assumed to have no effect).
///
/// Can be restricted to operate over only particular symbols by passing a
/// predicate to a \ref constant_propagator_ait constructor, in which case this
/// can be rendered sound by restricting it to non-address-taken variables.

#ifndef CPROVER_ANALYSES_CONSTANT_PROPAGATOR_H
#define CPROVER_ANALYSES_CONSTANT_PROPAGATOR_H
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