<html>
<head>
<base href="http://llvm.org/bugs/" />
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<body><table border="1" cellspacing="0" cellpadding="8">
<tr>
<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - debug info fail -- range based for loops and other stuff"
href="http://llvm.org/bugs/show_bug.cgi?id=19864">19864</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>debug info fail -- range based for loops and other stuff
</td>
</tr>
<tr>
<th>Product</th>
<td>clang
</td>
</tr>
<tr>
<th>Version</th>
<td>unspecified
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
<tr>
<th>OS</th>
<td>Linux
</td>
</tr>
<tr>
<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>-New Bugs
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>chandlerc@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvmbugs@cs.uiuc.edu
</td>
</tr>
<tr>
<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>So, I came here to file a bug about debug info for range-based for loops. I
wrote the following test case:
----
#include <vector>
#include <iostream>
int main() {
std::vector<int> v = {13, 21, 8, 3, 34, 1, 5, 2};
std::cout << "v = {" << v[0] << ", " << v[1] << ", " << v[2] << ", " << v[3]
<< ", " << v[4] << ", " << v[5] << ", " << v[6] << ", " << v[7]
<< "}\n";
int size = v.size();
if (v.size() > 3) {
int a = 0, b = 0;
for (int x : v)
if (x >= size)
++b;
else if (x >= 0)
++a;
std::cout << "a = " << a << "\n";
std::cout << "b = " << b << "\n";
}
}
----
Then I compiled and debugged it:
% clang++ -std=c++11 -g -o x x.cc
% gdb --args ./x
GNU gdb (GDB) 7.6.50.20130820-cvs
<snip>
Reading symbols from .../x...done.
(gdb) break main
Breakpoint 1 at 0x400b92: file x.cc, line 5.
(gdb) r
Starting program: .../x
<snip>
Breakpoint 1, main () at x.cc:5
5 std::vector<int> v = {13, 21, 8, 3, 34, 1, 5, 2};
(gdb) n
6 std::cout << "v = {" << v[0] << ", " << v[1] << ", " << v[2] << ", "
<< v[3]
(gdb)
7 << ", " << v[4] << ", " << v[5] << ", " << v[6] << ", " <<
v[7]
(gdb)
6 std::cout << "v = {" << v[0] << ", " << v[1] << ", " << v[2] << ", "
<< v[3]
(gdb)
7 << ", " << v[4] << ", " << v[5] << ", " << v[6] << ", " <<
v[7]
(gdb)
6 std::cout << "v = {" << v[0] << ", " << v[1] << ", " << v[2] << ", "
<< v[3]
(gdb)
7 << ", " << v[4] << ", " << v[5] << ", " << v[6] << ", " <<
v[7]
(gdb)
6 std::cout << "v = {" << v[0] << ", " << v[1] << ", " << v[2] << ", "
<< v[3]
(gdb)
7 << ", " << v[4] << ", " << v[5] << ", " << v[6] << ", " <<
v[7]
(gdb)
6 std::cout << "v = {" << v[0] << ", " << v[1] << ", " << v[2] << ", "
<< v[3]
WAT. I have no idea what happened here. But again, this is not why I wanted to
file the bug, its just something we should fix. Continuing with GDB...
(gdb)
v = {13, 21, 8, 3, 34, 1, 5, 2}
10 int size = v.size();
(gdb)
11 if (v.size() > 3) {
(gdb)
12 int a = 0, b = 0;
(gdb)
13 for (int x : v)
(gdb)
14 if (x >= size)
(gdb)
15 ++b;
(gdb)
17 ++a;
BUG: We never execute both ++b and ++a. This is a bogus line to jump to, I
think it's actually trying to jump to the "end" of the body of the range based
for loop, and has this as the source location or something. The *behavior* of
this program is entirely correct, but the debugger is lying to me.
(gdb)
13 for (int x : v)
(gdb)
14 if (x >= size)
(gdb)
15 ++b;
(gdb)
17 ++a;
And it happens on every loop where we execute "++b".
(gdb)
13 for (int x : v)
(gdb)
14 if (x >= size)
(gdb)
15 ++b;
(gdb)
17 ++a;
(gdb)
13 for (int x : v)
(gdb)
14 if (x >= size)
(gdb)
16 else if (x >= 0)
(gdb)
17 ++a;
(gdb)
13 for (int x : v)
But we only see one stop at that line when we execute "++a".
Let me know what else I can provide to help fix!</pre>
</div>
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