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Avoid exponential behavior in rust_evaluate_subexp

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The STRUCTOP_STRUCT case in rust_evaluate_subexp would evaluate its
LHS, and then, if it did not need Rust-specific treatment, it would
back up and re-evaluate the entire STRUCTOP_STRUCT part of the
expression using evaluate_subexp_standard.  This yields exponential
behavior and causes some expressions to evaluate extremely slowly.

The fix is to simply do the needed work inline.

This is PR rust/21483.

ChangeLog
2017-05-12  Tom Tromey  <tom@tromey.com>

	PR rust/21483:
	* rust-lang.c (rust_evaluate_subexp) <STRUCTOP_STRUCT>: Don't
	recurse, just call value_struct_elt directly.
This commit is contained in:
Tom Tromey 2017-05-11 22:22:36 -06:00
parent 68f2f2e308
commit 6830f270e7
2 changed files with 13 additions and 8 deletions
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6
gdb/ChangeLog
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@ -1,3 +1,9 @@
2017-05-12 Tom Tromey <tom@tromey.com>
PR rust/21483:
* rust-lang.c (rust_evaluate_subexp) <STRUCTOP_STRUCT>: Don't
recurse, just call value_struct_elt directly.
2017-05-12 Tom Tromey <tom@tromey.com>
* rust-lang.c (rust_dump_subexp_body) <STRUCTOP_ANONYMOUS,

15
gdb/rust-lang.c
View File

@ -1762,7 +1762,7 @@ tuple structs, and tuple-like enum variants"));
case STRUCTOP_STRUCT:
{
struct value* lhs;
struct value *lhs;
struct type *type;
int tem, pc;
@ -1771,16 +1771,14 @@ tuple structs, and tuple-like enum variants"));
(*pos) += 3 + BYTES_TO_EXP_ELEM (tem + 1);
lhs = evaluate_subexp (NULL_TYPE, exp, pos, noside);
const char *field_name = &exp->elts[pc + 2].string;
type = value_type (lhs);
if (TYPE_CODE (type) == TYPE_CODE_UNION
&& !rust_union_is_untagged (type))
{
int i, start;
struct disr_info disr;
struct type* variant_type;
char* field_name;
field_name = &exp->elts[pc + 2].string;
struct type *variant_type;
disr = rust_get_disr_info (type, value_contents (lhs),
value_embedded_offset (lhs),
@ -1817,9 +1815,10 @@ which has only anonymous fields"),
}
else
{
/* Field access in structs and untagged unions works like C. */
*pos = pc;
result = evaluate_subexp_standard (expect_type, exp, pos, noside);
result = value_struct_elt (&lhs, NULL, field_name, NULL,
"structure");
if (noside == EVAL_AVOID_SIDE_EFFECTS)
result = value_zero (value_type (result), VALUE_LVAL (result));
}
}
break;