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merge_value_sets: Avoid assignment when actually values can be moved #4169

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Merged
merged 1 commit into from
Mar 2, 2019
Merged

merge_value_sets: Avoid assignment when actually values can be moved #4169

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4 changes: 2 additions & 2 deletions src/goto-checker/symex_bmc.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -86,12 +86,12 @@ void symex_bmct::symex_step(
}
}

void symex_bmct::merge_goto(const goto_statet &goto_state, statet &state)
void symex_bmct::merge_goto(goto_statet &&goto_state, statet &state)
{
const goto_programt::const_targett prev_pc = goto_state.source.pc;
const guardt prev_guard = goto_state.guard;

goto_symext::merge_goto(goto_state, state);
goto_symext::merge_goto(std::move(goto_state), state);

PRECONDITION(prev_pc->is_goto());
if(
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2 changes: 1 addition & 1 deletion src/goto-checker/symex_bmc.h
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Expand Up @@ -94,7 +94,7 @@ class symex_bmct : public goto_symext
void symex_step(const get_goto_functiont &get_goto_function, statet &state)
override;

void merge_goto(const goto_statet &goto_state, statet &state) override;
void merge_goto(goto_statet &&goto_state, statet &state) override;

bool should_stop_unwind(
const symex_targett::sourcet &source,
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11 changes: 7 additions & 4 deletions src/goto-symex/goto_symex.h
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Expand Up @@ -232,12 +232,15 @@ class goto_symext

virtual void symex_assume(statet &, const exprt &cond);

// gotos
/// Merge all branches joining at the current program point. Applies
/// \ref merge_goto for each goto state (each of which corresponds to previous
/// branch).
void merge_gotos(statet &);

virtual void merge_goto(const goto_statet &goto_state, statet &);

void merge_value_sets(const goto_statet &goto_state, statet &dest);
/// Merge a single branch, the symbolic state of which is held in \p
/// goto_state, into the current overall symbolic state. \p goto_state is no
/// longer expected to be valid afterwards.
virtual void merge_goto(goto_statet &&goto_state, statet &);

void phi_function(const goto_statet &goto_state, statet &);

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21 changes: 7 additions & 14 deletions src/goto-symex/symex_goto.cpp
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Expand Up @@ -312,13 +312,13 @@ void goto_symext::merge_gotos(statet &state)

for(auto list_it = state_list.rbegin(); list_it != state_list.rend();
++list_it)
merge_goto(*list_it, state);
merge_goto(std::move(*list_it), state);

// clean up to save some memory
frame.goto_state_map.erase(state_map_it);
}

void goto_symext::merge_goto(const goto_statet &goto_state, statet &state)
void goto_symext::merge_goto(goto_statet &&goto_state, statet &state)
{
// check atomic section
if(state.atomic_section_id != goto_state.atomic_section_id)
Expand All @@ -329,7 +329,11 @@ void goto_symext::merge_goto(const goto_statet &goto_state, statet &state)
// do SSA phi functions
phi_function(goto_state, state);

merge_value_sets(goto_state, state);
// merge value sets
if(state.guard.is_false() && !goto_state.guard.is_false())
state.value_set = std::move(goto_state.value_set);
else if(!goto_state.guard.is_false())
state.value_set.make_union(goto_state.value_set);
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It would also make sense for make_union to not take a const ref, and use move instead. But that's maybe for another pull request.

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Making this impactful is a bigger task, because the internal representation of a value set is reference counted. I'll leave this for another time.


// adjust guard
state.guard|=goto_state.guard;
Expand All @@ -338,17 +342,6 @@ void goto_symext::merge_goto(const goto_statet &goto_state, statet &state)
state.depth=std::min(state.depth, goto_state.depth);
}

void goto_symext::merge_value_sets(const goto_statet &src, statet &dest)
{
if(dest.guard.is_false())
{
dest.value_set=src.value_set;
return;
}

dest.value_set.make_union(src.value_set);
}

/// Applies f to `(k, ssa, i, j)` if the first map maps k to (ssa, i) and
/// the second to (ssa', j). If the first map has an entry for k but not the
/// second one then j is 0, and when the first map has no entry for k then i = 0
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8 changes: 8 additions & 0 deletions src/pointer-analysis/value_set.h
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Expand Up @@ -47,6 +47,14 @@ class value_sett

virtual ~value_sett() = default;

value_sett(const value_sett &other) = default;

value_sett &operator=(value_sett &&other)
{
values = std::move(other.values);
return *this;
}

static bool field_sensitive(const irep_idt &id, const typet &type);

/// Matches the location_number field of the instruction that corresponds
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