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goto-convert: introduce assignment_lhs_needs_temporary #7047

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Merged
merged 1 commit into from
Sep 2, 2022
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goto-convert: introduce assignment_lhs_needs_temporary #7047

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2 changes: 1 addition & 1 deletion src/goto-programs/goto_clean_expr.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -384,7 +384,7 @@ void goto_convertt::clean_expr(
clean_expr(side_effect_assign.lhs(), dest, mode);
exprt lhs = side_effect_assign.lhs();

const bool must_use_rhs = needs_cleaning(lhs);
const bool must_use_rhs = assignment_lhs_needs_temporary(lhs);
if(must_use_rhs)
{
remove_function_call(
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9 changes: 9 additions & 0 deletions src/goto-programs/goto_convert_class.h
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Expand Up @@ -89,6 +89,15 @@ class goto_convertt:public messaget

static bool needs_cleaning(const exprt &expr);

// Do we need to introduce a temporary for the value of an assignment
// to the given lhs? E.g., a[i] needs a temporary as its value may change
// when i is changed; likewise, *p needs a temporary as its value may change
// when p is changed.
static bool assignment_lhs_needs_temporary(const exprt &lhs)
{
return lhs.id() != ID_symbol;
}

void make_temp_symbol(
exprt &expr,
const std::string &suffix,
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10 changes: 7 additions & 3 deletions src/goto-programs/goto_convert_side_effect.cpp
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Expand Up @@ -50,7 +50,9 @@ void goto_convertt::remove_assignment(
{
auto &old_assignment = to_side_effect_expr_assign(expr);

if(result_is_used && !address_taken && needs_cleaning(old_assignment.lhs()))
if(
result_is_used && !address_taken &&
assignment_lhs_needs_temporary(old_assignment.lhs()))
{
if(!old_assignment.rhs().is_constant())
make_temp_symbol(old_assignment.rhs(), "assign", dest, mode);
Expand Down Expand Up @@ -122,7 +124,9 @@ void goto_convertt::remove_assignment(
exprt rhs = binary_exprt{binary_expr.op0(), new_id, binary_expr.op1()};
rhs.add_source_location() = expr.source_location();

if(result_is_used && !address_taken && needs_cleaning(binary_expr.op0()))
if(
result_is_used && !address_taken &&
assignment_lhs_needs_temporary(binary_expr.op0()))
{
make_temp_symbol(rhs, "assign", dest, mode);
replacement_expr_opt = rhs;
Expand Down Expand Up @@ -237,7 +241,7 @@ void goto_convertt::remove_pre(
}

const bool cannot_use_lhs =
result_is_used && !address_taken && needs_cleaning(lhs);
result_is_used && !address_taken && assignment_lhs_needs_temporary(lhs);
if(cannot_use_lhs)
make_temp_symbol(rhs, "pre", dest, mode);

Expand Down