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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - AST MatchFinder Does not Do Pre-order Traversal"
href="https://bugs.llvm.org/show_bug.cgi?id=39190">39190</a>
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<tr>
<th>Summary</th>
<td>AST MatchFinder Does not Do Pre-order Traversal
</td>
</tr>
<tr>
<th>Product</th>
<td>clang
</td>
</tr>
<tr>
<th>Version</th>
<td>7.0
</td>
</tr>
<tr>
<th>Hardware</th>
<td>All
</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>
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<th>Component</th>
<td>libclang
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>lunastorm@lunastorm.tw
</td>
</tr>
<tr>
<th>CC</th>
<td>klimek@google.com, llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>The documentation of AST MatchFinder says:
"The order of matches is guaranteed to be equivalent to doing a pre-order
traversal on the AST"
<a href="https://clang.llvm.org/doxygen/classclang_1_1ast__matchers_1_1MatchFinder.html#details">https://clang.llvm.org/doxygen/classclang_1_1ast__matchers_1_1MatchFinder.html#details</a>
After upgrade to Clang7, we noticed that the match order is changed.
For this example:
void foo()
{
for (;;) {
break;
}
for (;;) {
break;
}
return;
}
Clang6's clang-query result of "m stmt()" is:
Match #1:
/Users/lunastorm/temp/foo.c:2:1: note: "root" binds here
{
^
Match #2:
/Users/lunastorm/temp/foo.c:3:5: note: "root" binds here
for (;;) {
^~~~~~~~~~
Match #3:
/Users/lunastorm/temp/foo.c:3:14: note: "root" binds here
for (;;) {
^
Match #4:
/Users/lunastorm/temp/foo.c:4:9: note: "root" binds here
break;
^~~~~
Match #5:
/Users/lunastorm/temp/foo.c:6:5: note: "root" binds here
for (;;) {
^~~~~~~~~~
Match #6:
/Users/lunastorm/temp/foo.c:6:14: note: "root" binds here
for (;;) {
^
Match #7:
/Users/lunastorm/temp/foo.c:7:9: note: "root" binds here
break;
^~~~~
Match #8:
/Users/lunastorm/temp/foo.c:9:5: note: "root" binds here
return;
^~~~~~
8 matches.
====
While Clang7's clang-query result of "m stmt()" gives:
Match #1:
/Users/lunastorm/temp/foo.c:2:1: note: "root" binds here
{
^
Match #2:
/Users/lunastorm/temp/foo.c:3:5: note: "root" binds here
for (;;) {
^~~~~~~~~~
Match #3:
/Users/lunastorm/temp/foo.c:6:5: note: "root" binds here
for (;;) {
^~~~~~~~~~
Match #4:
/Users/lunastorm/temp/foo.c:9:5: note: "root" binds here
return;
^~~~~~
Match #5:
/Users/lunastorm/temp/foo.c:3:14: note: "root" binds here
for (;;) {
^
Match #6:
/Users/lunastorm/temp/foo.c:4:9: note: "root" binds here
break;
^~~~~
Match #7:
/Users/lunastorm/temp/foo.c:6:14: note: "root" binds here
for (;;) {
^
Match #8:
/Users/lunastorm/temp/foo.c:7:9: note: "root" binds here
break;
^~~~~
8 matches.
====
We have a tool based on MatchFinder and relies on the pre-order traversal
guarantee.
It seems that it is related to r326624 which adds data recursion support to
TraverseStmt. Without this change there will be a stack overflow in
<a class="bz_bug_link
bz_status_RESOLVED bz_closed"
title="RESOLVED FIXED - Nesting of empty case-labels in AST"
href="show_bug.cgi?id=36581">https://bugs.llvm.org/show_bug.cgi?id=36581</a>
Can the MatchFinder remain the same traverse order guarantee by default, and
take a MatchFinderOption to supply the Queue parameter of TraverseStmt
optionally?
Or the RAV can be modified to traverse in pre-order without hitting stack
limit?
Thanks!</pre>
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