<html>
<head>
<base href="http://llvm.org/bugs/" />
</head>
<body><table border="1" cellspacing="0" cellpadding="8">
<tr>
<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - Implement support in clang-cl for the /GT option"
href="http://llvm.org/bugs/show_bug.cgi?id=19177">19177</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>Implement support in clang-cl for the /GT option
</td>
</tr>
<tr>
<th>Product</th>
<td>new-bugs
</td>
</tr>
<tr>
<th>Version</th>
<td>unspecified
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
<tr>
<th>OS</th>
<td>All
</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>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>rafael.espindola@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>bigcheesegs@gmail.com, llvmbugs@cs.uiuc.edu, rnk@google.com
</td>
</tr>
<tr>
<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>The option is defined in
<a href="http://msdn.microsoft.com/en-us/library/6e298fy4.aspx">http://msdn.microsoft.com/en-us/library/6e298fy4.aspx</a>
In summary, it means that we cannot assume that the address of a tls doesn't
change across a call, since the call might causes a fiber to move to another
thread.
This has implications for both IR and codegen. For the IR issue, consider
struct foo {
int v[10];
};
static __thread struct foo var;
struct foo *h(void) { return &var; }
void f(int *);
void g(int x, int y) {
for (int i = 0; i < x; ++i) {
f(&var.v[y]);
}
}
This currently produces
------------------------------
for.body.lr.ph:
...
%arrayidx = getelementptr inbounds %struct.foo* @var, i64 0, i32 0, i64
%idxprom
br label %for.body
for.body:
...
tail call void @f(i32* %arrayidx)
...
br i1 %exitcond, label %for.end, label %for.body
----------------------------------
but the address is not actually loop invariant.
For codegen, consider
static __thread int var;
int *h(void) { return &var; }
void f(int);
void g(void) {
f(var);
f(var);
}
We only call __tls_get_addr@PLT once with the local dynamic model.
We chatted a bit about it and it looks like we would need to change clang's
IRGen when the option is given to use an intrinsic to get the actual address.
Something like
%addr = llvm.get_tls_addr(@var)
so that the optimizers know that %addr can be different in each loop iteration.</pre>
</div>
</p>
<hr>
<span>You are receiving this mail because:</span>
<ul>
<li>You are on the CC list for the bug.</li>
</ul>
</body>
</html>