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compiler: don't incorrectly evaluate range variable

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The language spec says that in `for i = range x`, in which there is no
    second iteration variable, if len(x) is constant, then x is not
    evaluated.  This only matters when x is an expression that panics but
    whose type is an array type; in such a case, we should not evaluate x,
    since len of any array type is a constant.
    
    Fixes golang/go#22313
    
    Reviewed-on: https://go-review.googlesource.com/91555

From-SVN: r257330
This commit is contained in:
Ian Lance Taylor 2018-02-02 13:44:41 +00:00
parent eece7fe533
commit 31766e6833
2 changed files with 37 additions and 13 deletions
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2
gcc/go/gofrontend/MERGE
View file

@ -1,4 +1,4 @@
b332ba2f0d0302eeb01a228c217928296cec56f6
981e6621bcd48670d0b58e51e9eeffe549725378
The first line of this file holds the git revision number of the last
merge done from the gofrontend repository.

48
gcc/go/gofrontend/statements.cc
View file

@ -5307,19 +5307,33 @@ For_range_statement::do_lower(Gogo* gogo, Named_object*, Block* enclosing,
return Statement::make_error_statement(this->location());
}
// If there is only one iteration variable, and len(this->range_) is
// constant, then we do not evaluate the range variable. len(x) is
// a contant if x is a string constant or if x is an array. If x is
// a constant then evaluating it won't make any difference, so the
// only case to consider is when x is an array.
bool eval = true;
if (this->value_var_ == NULL
&& range_type->array_type() != NULL
&& !range_type->is_slice_type())
eval = false;
Location loc = this->location();
Block* temp_block = new Block(enclosing, loc);
Named_object* range_object = NULL;
Temporary_statement* range_temp = NULL;
Var_expression* ve = this->range_->var_expression();
if (ve != NULL)
range_object = ve->named_object();
else
if (eval)
{
range_temp = Statement::make_temporary(NULL, this->range_, loc);
temp_block->add_statement(range_temp);
this->range_ = NULL;
Var_expression* ve = this->range_->var_expression();
if (ve != NULL)
range_object = ve->named_object();
else
{
range_temp = Statement::make_temporary(NULL, this->range_, loc);
temp_block->add_statement(range_temp);
this->range_ = NULL;
}
}
Temporary_statement* index_temp = Statement::make_temporary(index_type,
@ -5474,12 +5488,22 @@ For_range_statement::lower_range_array(Gogo* gogo,
Block* init = new Block(enclosing, loc);
Expression* ref = this->make_range_ref(range_object, range_temp, loc);
range_temp = Statement::make_temporary(NULL, ref, loc);
Expression* len_call = this->call_builtin(gogo, "len", ref, loc);
Expression* len_arg;
if (range_object == NULL && range_temp == NULL)
{
// Don't evaluate this->range_, just get its length.
len_arg = this->range_;
}
else
{
Expression* ref = this->make_range_ref(range_object, range_temp, loc);
range_temp = Statement::make_temporary(NULL, ref, loc);
init->add_statement(range_temp);
len_arg = ref;
}
Expression* len_call = this->call_builtin(gogo, "len", len_arg, loc);
Temporary_statement* len_temp = Statement::make_temporary(index_temp->type(),
len_call, loc);
init->add_statement(range_temp);
init->add_statement(len_temp);
Expression* zexpr = Expression::make_integer_ul(0, NULL, loc);
@ -5495,7 +5519,7 @@ For_range_statement::lower_range_array(Gogo* gogo,
// Set *PCOND to
// index_temp < len_temp
ref = Expression::make_temporary_reference(index_temp, loc);
Expression* ref = Expression::make_temporary_reference(index_temp, loc);
Expression* ref2 = Expression::make_temporary_reference(len_temp, loc);
Expression* lt = Expression::make_binary(OPERATOR_LT, ref, ref2, loc);