<html><head><meta http-equiv="Content-Type" content="text/html charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class="">Hi Rachel,<div class=""><br class=""></div><div class="">The CFG encodes control flow between both statements and (important) sub-expressions. It’s been a while since I’ve touched the CFG, but IIRC we don’t do a complete linearization of all expressions — but we do for many of them.</div><div class=""><br class=""></div><div class="">Let’s take your example:</div><div class=""><br class=""></div><div class="">[B1]<br class=""> 1: pow(2., 3)<br class=""> 2: double i = pow(2., 3);</div><div class=""><br class=""></div><div class="">This is actually an expression, B1.1, and its containing statement, B1.2. The CFG encodes that “pow(2., 3)” happens before the initialization of ‘i’. This is NOT the case of the same thing being added twice. The idea is that an analysis will know the call happens first. By the time a statement appears in the CFG, it is a precondition that any sub-expressions that appear in the CFG will dominate the statement appearing in the CFG. Again, we don’t do a complete linearization (because that would be unnecessary) but we do for things like calls, binary expressions, and anything that has control flow like ‘&&’, etc.</div><div class=""><br class=""></div><div class="">The way this SHOULD be printed up is something like:</div><div class=""><br class=""></div><div class=""> 1: i++<br class=""> 2: k--<br class=""> 3: [B2.1], [B2.2]</div><div class=""><br class=""></div><div class="">In this case we see that the sub-expression ‘i++’ gets evaluated first, followed by ‘k—‘, and then the comma expression gets evaluated as a whole after both of these.</div><div class=""><br class=""></div><div class="">Does that help? It is not the case that the same exact thing is added twice.</div><div class=""><br class=""></div><div class="">Ted</div><div class=""><br class=""></div><div class=""><div><br class=""><blockquote type="cite" class=""><div class="">On Jun 7, 2017, at 7:17 AM, Rachel HaCohen (rahacohe) via cfe-dev <<a href="mailto:cfe-dev@lists.llvm.org" class="">cfe-dev@lists.llvm.org</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div class="WordSection1" style="page: WordSection1; font-family: SFHello-Regular; font-size: 15px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;"><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class="">Hello all,<o:p class=""></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class="">I’m writing a tool that uses the CFG with different functions.<o:p class=""></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class="">I have a problem that when iterating over the elements of a CFGBlock, some of the statements appear twice.<o:p class=""></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class="">It is most prevalent in function calls but I saw it in some other cases as well.<o:p class=""></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class="">For example, the following code:<o:p class=""></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""> <o:p class=""></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-family: 'Courier New';" class="">double i = pow(2.0, 3);</span><o:p class=""></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""> <o:p class=""></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class="">will create two elements in the CFGBlock:<o:p class=""></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-family: 'Courier New';" class="">[B1]</span><o:p class=""></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-family: 'Courier New';" class=""> 1: pow(2., 3)</span><o:p class=""></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-family: 'Courier New';" class=""> 2: double i = pow(2., 3);</span><o:p class=""></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""> <o:p class=""></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class="">And when I try to reproduce the code from this block (by iterating over the elements and pretty print them), I get two function calls:<o:p class=""></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-family: 'Courier New';" class="">pow(2., 3);</span><o:p class=""></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-family: 'Courier New';" class="">double i = pow(2., 3);</span><o:p class=""></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""> <o:p class=""></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class="">I saw the same behavior also in binary operator when the opcode is a comma and in conditional operator.<o:p class=""></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class="">Here are some examples:<o:p class=""></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class="">1)<o:p class=""></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-family: 'Courier New';" class="">int i, k = 10;</span><o:p class=""></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-family: 'Courier New';" class="">for (i = 0; i < 10; i++, k--){</span><o:p class=""></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; text-indent: 0.5in;" class=""><span style="font-family: 'Courier New';" class="">// some code</span><o:p class=""></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-family: 'Courier New';" class="">}</span><o:p class=""></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""> <o:p class=""></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class="">The block that corresponds to the step of the for loop looks like that:<o:p class=""></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-family: 'Courier New';" class="">[B2]</span><o:p class=""></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-family: 'Courier New';" class=""> 1: i++</span><o:p class=""></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-family: 'Courier New';" class=""> 2: k--</span><o:p class=""></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-family: 'Courier New';" class=""> 3: [B2.1], [B2.2]</span><o:p class=""></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-family: 'Courier New';" class=""> </span><o:p class=""></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class="">Which creates the code:<o:p class=""></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-family: 'Courier New';" class="">i++;</span><o:p class=""></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-family: 'Courier New';" class="">k--;</span><o:p class=""></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-family: 'Courier New';" class="">i++, k--;</span><o:p class=""></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-family: 'Courier New';" class=""> </span><o:p class=""></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class="">2)<o:p class=""></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-family: 'Courier New';" class="">return a > 0? a : -a;</span><o:p class=""></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""> <o:p class=""></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class="">Creates this block:<o:p class=""></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-family: 'Courier New';" class="">1: [B4.2] ? [B2.1] : [B3.1]</span><o:p class=""></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-family: 'Courier New';" class=""> 2: return [B1.1];</span><o:p class=""></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""> <o:p class=""></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class="">Which pretty prints the following code:<o:p class=""></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-family: 'Courier New';" class="">a > 0 ? a : -a;</span><o:p class=""></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-family: 'Courier New';" class="">return a > 0 ? a : -a;</span><o:p class=""></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-family: 'Courier New';" class=""> </span><o:p class=""></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-family: 'Courier New';" class=""> </span><o:p class=""></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class="">I suspect that the reason for this behavior is that the CFG is built recursively and some of the statements are visited and appended twice to the block.<o:p class=""></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class="">In the case of the binary operator with comma, I solved this problem by removing the call to appendStmt in the code below (Which is in CFGBuilder::VisitBinaryOperator() in CFG.cpp file)<o:p class=""></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""> <o:p class=""></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-family: 'Courier New';" class="">if (B->getOpcode() == BO_Comma) { // ,</span><o:p class=""></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-family: 'Courier New';" class=""> autoCreateBlock();</span><o:p class=""></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-family: 'Courier New';" class=""> //appendStmt(Block, B);</span><o:p class=""></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-family: 'Courier New';" class=""> addStmt(B->getRHS());</span><o:p class=""></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-family: 'Courier New';" class=""> return addStmt(B->getLHS());</span><o:p class=""></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-family: 'Courier New';" class=""> }</span><o:p class=""></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-family: 'Courier New';" class=""> </span><o:p class=""></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class="">I tried to solve the problem also by changing VisitCallExpr() and VisitConditioalOperator() but couldn’t solve it there.<o:p class=""></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class="">I would appreciate any help and insights about this issue.<o:p class=""></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class="">Thanks,<o:p class=""></o:p></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class="">Rachel.<span class="Apple-converted-space"> </span><o:p class=""></o:p></div></div><span style="font-family: SFHello-Regular; font-size: 15px; font-style: normal; font-variant-caps: normal; font-weight: normal; 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