From 6830f270e7b6676e7a77c1b8080941e35003d918 Mon Sep 17 00:00:00 2001 From: Tom Tromey Date: Thu, 11 May 2017 22:22:36 -0600 Subject: [PATCH] Avoid exponential behavior in rust_evaluate_subexp 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 PR rust/21483: * rust-lang.c (rust_evaluate_subexp) : Don't recurse, just call value_struct_elt directly. --- gdb/ChangeLog | 6 ++++++ gdb/rust-lang.c | 15 +++++++-------- 2 files changed, 13 insertions(+), 8 deletions(-) diff --git a/gdb/ChangeLog b/gdb/ChangeLog index c2d3f2d..71aea52 100644 --- a/gdb/ChangeLog +++ b/gdb/ChangeLog @@ -1,5 +1,11 @@ 2017-05-12 Tom Tromey + PR rust/21483: + * rust-lang.c (rust_evaluate_subexp) : Don't + recurse, just call value_struct_elt directly. + +2017-05-12 Tom Tromey + * rust-lang.c (rust_dump_subexp_body) : Fix. diff --git a/gdb/rust-lang.c b/gdb/rust-lang.c index b4a529d..898edda 100644 --- a/gdb/rust-lang.c +++ b/gdb/rust-lang.c @@ -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; -- 2.7.4