在C++14中使用泛型lambda的奇怪编译器行为

Question

最近，当我使用通用lambda (C++14特性，允许使用auto作为lambda参数)时，我遇到了GCC的一个有趣的怪癖。它似乎使用自动而不是类型，在某种程度上影响“此”指针如何被捕获。我在下面的例子中重现了问题：

#include <cstdio>

class A { private:
    void method(int i) {
        printf("Method Call %d",i);
    }

public:
    void publicMethod() {
        auto lambda = [&] (const int k) { //problematic line
            method(k);                    //problematic line
        };
        lambda(42);
    } };

int main() {
    A a;
    a.publicMethod();
    return 0; }

上面的代码有效。当我将“有问题的行”改为：

        auto lambda = [&] (const auto k) { //problematic line
            method(k);                     //problematic line

它不再编译了，但是添加了“这个”指针：

        auto lambda = [&] (const auto k) { //problematic line
            this->method(k);               //problematic line

解决这个问题。我的问题是:这种行为有什么合理的理由吗？或者是GCC的非理性怪癖(也许应该被报道)？

下面是编译器在不使用auto而不使用this的情况下的输出

test.cpp: In lambda function:
test.cpp:12:13: internal compiler error: Segmentation fault
             method(k);
             ^
0x848ecc crash_signal
    ../../src/gcc/toplev.c:383
0xea28e5 size_binop_loc(unsigned int, tree_code, tree_node*, tree_node*)
    ../../src/gcc/fold-const.c:1768
0xee86d7 gimplify_compound_lval
    ../../src/gcc/gimplify.c:2039
0xee86d7 gimplify_expr(tree_node**, gimple_statement_base**, gimple_statement_base**, bool (*)(tree_node*), int)
    ../../src/gcc/gimplify.c:8052
0xeeb639 gimplify_arg(tree_node**, gimple_statement_base**, unsigned int)
    ../../src/gcc/gimplify.c:2271
0xeeb639 gimplify_call_expr
    ../../src/gcc/gimplify.c:2477
0xee89f2 gimplify_expr(tree_node**, gimple_statement_base**, gimple_statement_base**, bool (*)(tree_node*), int)
    ../../src/gcc/gimplify.c:8071
0xee8da7 gimplify_stmt(tree_node**, gimple_statement_base**)
    ../../src/gcc/gimplify.c:5519
0xee8da7 gimplify_cleanup_point_expr
    ../../src/gcc/gimplify.c:5295
0xee8da7 gimplify_expr(tree_node**, gimple_statement_base**, gimple_statement_base**, bool (*)(tree_node*), int)
    ../../src/gcc/gimplify.c:8463
0xee7ace gimplify_stmt(tree_node**, gimple_statement_base**)
    ../../src/gcc/gimplify.c:5519
0xee94db gimplify_bind_expr
    ../../src/gcc/gimplify.c:1136
0xee94db gimplify_expr(tree_node**, gimple_statement_base**, gimple_statement_base**, bool (*)(tree_node*), int)
    ../../src/gcc/gimplify.c:8297
0xee757f gimplify_stmt(tree_node**, gimple_statement_base**)
    ../../src/gcc/gimplify.c:5519
0xee757f gimplify_body(tree_node*, bool)
    ../../src/gcc/gimplify.c:9234
0xee72fd gimplify_function_tree(tree_node*)
    ../../src/gcc/gimplify.c:9388
0xe195e0 cgraph_node::analyze()
    ../../src/gcc/cgraphunit.c:634
0xe195e0 analyze_functions
    ../../src/gcc/cgraphunit.c:1024
0x127d1ab symbol_table::finalize_compilation_unit()
    ../../src/gcc/cgraphunit.c:2453
0xd37db5 cp_write_global_declarations()
    ../../src/gcc/cp/decl2.c:4843
Please submit a full bug report,
with preprocessed source if appropriate.
Please include the complete backtrace with any bug report.
See <file:///usr/share/doc/gcc-5/README.Bugs> for instructions.

用GCC 5.3.1编制

Answer 1

谢谢你的评论。的确，这是GCC的错误--我的同事刚刚把这件事报告给GCC支持：

bug.cgi?id=69977