<div dir="ltr"><div>Hi!</div><div><br></div><div>There are two tools in the analyzer to help these problems but both are off by default as they would need some additional improvements and testing. <br></div><div><br></div><div>One is loop unrolling which (when turned on) will detect specific loop patterns and unroll them completely (instead of stopping after 4 iterations).</div><div>The other is loop widening which involves restarting the analysis after the loop. While this increases the coverage of the analysis it can also trigger additional false positives as a large portion of the state needs to be invalidated to restart the analysis. Making this invalidation less severe is one way to improve the situation.</div><div><br></div><div>Cheers,</div><div>Gabor<br></div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Thu, 30 Jul 2020 at 14:32, Denis Petrov via cfe-dev <<a href="mailto:cfe-dev@lists.llvm.org">cfe-dev@lists.llvm.org</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
<div dir="ltr" style="font-size:12pt;color:rgb(0,0,0);background-color:rgb(255,255,255);font-family:Calibri,Arial,Helvetica,sans-serif">
<p>In addition to my previous letter. I'm very concerned that we may have no chance to analyze a big chunk of code in this case:<br>
</p>
<blockquote style="margin:0px 0px 0px 40px;border:medium none;padding:0px">
<div><span style="font-family:Consolas,monospace;font-size:9pt"></span></div>
<div><span style="font-size:9pt"><span style="font-family:Consolas,monospace"><span style="font-family:Consolas,monospace">void clang_analyzer_warnIfReached();</span></span><br style="font-family:Consolas,monospace">
<span style="font-family:Consolas,monospace"><span style="font-family:Consolas,monospace">int f()</span></span><br style="font-family:Consolas,monospace">
<span style="font-family:Consolas,monospace"><span style="font-family:Consolas,monospace">{</span></span><br style="font-family:Consolas,monospace">
<span style="font-family:Consolas,monospace"><span style="font-family:Consolas,monospace"> int i = 0;</span></span><br style="font-family:Consolas,monospace">
<span style="font-family:Consolas,monospace"><span style="font-family:Consolas,monospace"> for(int i = 0; i < 100; i++){</span></span><br style="font-family:Consolas,monospace">
<span style="font-family:Consolas,monospace"><span style="font-family:Consolas,monospace"> if(i > 10){</span></span><br style="font-family:Consolas,monospace">
<span style="font-family:Consolas,monospace"><span style="font-family:Consolas,monospace"> clang_analyzer_warnIfReached();</span></span><br style="font-family:Consolas,monospace">
<span style="font-family:Consolas,monospace"><span style="font-family:Consolas,monospace"> // a lot of code will never be analyzed</span></span><br style="font-family:Consolas,monospace">
<span style="font-family:Consolas,monospace"><span style="font-family:Consolas,monospace"> }</span></span><br style="font-family:Consolas,monospace">
<span style="font-family:Consolas,monospace"><span style="font-family:Consolas,monospace"> }</span></span><br style="font-family:Consolas,monospace">
<span style="font-family:Consolas,monospace"><span style="font-family:Consolas,monospace">}</span></span></span></div>
</blockquote>
<p>Why don't we analyze loop bodies as functions, just substitute a var `i` <span style="font-family:Calibri,Arial,Helvetica,sans-serif;font-size:16px;background-color:rgb(255,255,255)">
with </span><span style="font-family:Calibri,Arial,Helvetica,sans-serif;font-size:16px;background-color:rgb(255,255,255)">s</span><span style="font-family:Calibri,Arial,Helvetica,sans-serif;font-size:16px;background-color:rgb(255,255,255)">ymbols(or
constraint ranges)</span> after reaching the limits, not generating a sinks instead?<br>
</p>
<p>Or there are somewhere already disscussed plans for improvement?<br>
</p>
<p><br>
</p>
<div id="gmail-m_-4775467890160906839Signature">
<div name="divtagdefaultwrapper">
<hr>
<div><b>Denys Petrov</b></div>
<div>Senior С++ Developer | Kharkiv, Ukraine</div>
<div><br>
</div>
<div></div>
</div>
</div>
<div style="color:rgb(33,33,33)">
<hr style="display:inline-block;width:98%">
<div id="gmail-m_-4775467890160906839divRplyFwdMsg" dir="ltr"><font style="font-size:11pt" face="Calibri, sans-serif" color="#000000"><b>От:</b> Artem Dergachev <<a href="mailto:noqnoqneo@gmail.com" target="_blank">noqnoqneo@gmail.com</a>><br>
<b>Отправлено:</b> 28 июля 2020 г. 22:34<br>
<b>Кому:</b> Denis Petrov; cfe-dev<br>
<b>Тема:</b> Re: [cfe-dev] [analyzer] How to analyzer the code after an indefinite loop?</font>
<div> </div>
</div>
<div>
<div style="font-size:9pt;font-family:"Calibri",sans-serif">
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<div>Here's how you can find this out with the help of ExprInspection:<br>
<br>
<br>
$ cat test.c<br>
<br>
int f(int x, int flag)<br>
{<br>
int i = 0;<br>
while(i < x)<br>
i++;<br>
<br>
clang_analyzer_warnIfReached();<br>
}<br>
<br>
<br>
$ clang --analyze -Xclang -analyzer-checker=debug.ExprInspection test.c<br>
<br>
test.c:7:3: warning: REACHABLE [debug.ExprInspection]<br>
clang_analyzer_warnIfReached();<br>
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~<br>
1 warning generated.<br>
<br>
<br>
Here's a slightly more interesting experiment:<br>
<br>
<br>
$ cat test.c<br>
<br>
int f(int x, int flag)<br>
{<br>
int i = 0;<br>
while(i < x)<br>
i++;<br>
<br>
if (flag) {<br>
clang_analyzer_warnIfReached();<br>
clang_analyzer_numTimesReached();<br>
return i;<br>
} else {<br>
clang_analyzer_warnIfReached();<br>
clang_analyzer_numTimesReached();<br>
return 0;<br>
}<br>
}<br>
<br>
<br>
$ clang --analyze -Xclang -analyzer-checker=debug.ExprInspection test.c<br>
<br>
test.c:8:5: warning: REACHABLE [debug.ExprInspection]<br>
clang_analyzer_warnIfReached();<br>
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~<br>
test.c:9:5: warning: 4 [debug.ExprInspection]<br>
clang_analyzer_numTimesReached();<br>
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~<br>
test.c:12:5: warning: REACHABLE [debug.ExprInspection]<br>
clang_analyzer_warnIfReached();<br>
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~<br>
test.c:13:5: warning: 1 [debug.ExprInspection]<br>
clang_analyzer_numTimesReached();<br>
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~<br>
4 warnings generated.<br>
<br>
<br>
Will you be able to figure out why is one branch reached 4 times while the other branch is reached only once? You can find all your answers on the exploded graph dump.<br>
<br>
<br>
<div>On 7/28/20 5:59 AM, Denis Petrov via cfe-dev wrote:<br>
</div>
<blockquote type="cite">
<p>Hi, community!<br>
</p>
<p><br>
</p>
<p>A quick question.<br>
</p>
<p><br>
</p>
<p>Is CSA Core able to analyze the code after some indefinite loop?<br>
</p>
<p>E.g.<br>
</p>
<div><span style="font-family:Consolas,monospace;font-size:9pt"><span style="font-family:Consolas,monospace"><span style="font-family:Consolas,monospace"><span style="font-family:Consolas,monospace">void f(int x)</span></span></span></span></div>
<div><span style="font-family:Consolas,monospace;font-size:9pt"><span style="font-family:Consolas,monospace"><span style="font-family:Consolas,monospace"><span style="font-family:Consolas,monospace"><span style="font-family:Consolas,monospace">{</span></span></span></span><br style="font-family:Consolas,monospace">
</span></div>
<div><span style="font-family:Consolas,monospace;font-size:9pt"><span style="font-family:Consolas,monospace"><span style="font-family:Consolas,monospace"><span style="font-family:Consolas,monospace"><span style="font-family:Consolas,monospace"> int i = 0;</span></span></span></span><br style="font-family:Consolas,monospace">
</span></div>
<div><span style="font-family:Consolas,monospace;font-size:9pt"><span style="font-family:Consolas,monospace"><span style="font-family:Consolas,monospace"><span style="font-family:Consolas,monospace"> while(i < x)</span></span></span></span></div>
<div><span style="font-size:9pt"><span style="font-family:Consolas,monospace"><span style="font-family:Consolas,monospace"> i++;</span></span><br style="font-family:Consolas,monospace">
</span></div>
<div><span style="font-family:Consolas,monospace;font-size:9pt"><span style="font-family:Consolas,monospace"><span style="font-family:Consolas,monospace"><span style="font-family:Consolas,monospace"><span style="font-family:Consolas,monospace"> // Interested
in some code here!!</span></span></span></span><br style="font-family:Consolas,monospace">
</span></div>
<div><span style="font-family:Consolas,monospace;font-size:9pt"><span style="font-family:Consolas,monospace"><span style="font-family:Consolas,monospace"><span style="font-family:Consolas,monospace">}</span></span></span></span><br>
</div>
<p><br>
</p>
<p>I found that Exploded graph grows going through the loop 4 times and then stops to analyze the code further.<br>
</p>
<p>P.S. I know about -<span style="color:rgb(36,41,46);font-family:SFMono-Regular,Consolas,"Liberation Mono",Menlo,monospace;font-size:12px;white-space:pre-wrap;background-color:rgb(255,255,255)">analyzer-max-loop</span>(4).<br>
</p>
<div id="gmail-m_-4775467890160906839Signature">
<div name="divtagdefaultwrapper">
<hr>
<div><b>Denys Petrov</b></div>
<div>Senior С++ Developer | Kharkiv, Ukraine</div>
<div><br>
</div>
</div>
</div>
<br>
<fieldset></fieldset>
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