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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">If we had a very naïve way of generating IR, in the 'continue' case you would actually see TWO branch instructions: one to implement the 'continue' statement,
and one as part of the control flow of the 'for' loop. The branch for the 'continue' statement would have the source location of the 'continue' and the branch for the control-flow of the 'for' loop would have the source location of the right brace.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Clang is smart enough that in the 'continue' example, it knows not to emit the second branch (it would be unreachable).<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">--paulr<o:p></o:p></span></p>
<p class="MsoNormal"><a name="_MailEndCompose"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></a></p>
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<p class="MsoNormal"><b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif"">From:</span></b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif""> Frozen [mailto:bluechristlove@163.com]
<br>
<b>Sent:</b> Saturday, June 03, 2017 8:13 AM<br>
<b>To:</b> Marcin Słowik<br>
<b>Cc:</b> llvm-dev@lists.llvm.org; Robinson, Paul<br>
<b>Subject:</b> Re:Re: Re: [llvm-dev] How the LLVM handle the debug location information of continue keyword and right brace(loop end location)?<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black">If without any brace, the br should correspond to doStuff() in your case. However, maybe I don't list my concern and question very clearly, it is my mistake and
I apologize for it. <o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black">Let me show you more details:<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black">1.int main()<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black">2.{<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black">3. int i;<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black">4.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black">5. for (i = 0; i < 256; i++) {<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black">6. }<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black">7.}<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black">; <label>:6: ; preds = %3<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black">
<b>br label %7, !dbg !23</b><o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black">; <label>:7: ; preds = %6<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black"> %8 = load i32, i32* %2, align 4, !dbg !25<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black"> %9 = add nsw i32 %8, 1, !dbg !25<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black"> store i32 %9, i32* %2, align 4, !dbg !25<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black"> br label %3, !dbg !27, !llvm.loop !28<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black">!23 = !DILocation(<b>line: 6</b>, column: 1, scope: !24)<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black">You can see that this br instruction corresponds to right brace(i.e. line 6).<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black">Let us see:<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black">1.int main()<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black">2.{<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black">3. int i;<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black">4.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black">5. for (i = 0; i < 256; i++) {<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black">6. continue;<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black">7. }<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black">8. }<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black">; <label>:6: ; preds = %3<o:p></o:p></span></p>
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<p class="MsoNormal"><b><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black"> br label %7, !dbg !23</span></b><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black"><o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black">; <label>:7: ; preds = %6<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black"> %8 = load i32, i32* %2, align 4, !dbg !25<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black"> %9 = add nsw i32 %8, 1, !dbg !25<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black"> store i32 %9, i32* %2, align 4, !dbg !25<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black"> br label %3, !dbg !27, !llvm.loop !28<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black">!23 = !DILocation(<b>line: 6</b>, column: 1, scope: !24)<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black">You can see that this br instruction corresponds to continue statement (i.e. line 6).<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black">But, the result is: the first case line 6 right brace will not generated(it make sense and just group), but the latter case is line 6 continue and will generate
location information for debugger. My question is they are the same but will be treated differently, I do not know how LLVM backend treat these two IR. Maybe I think these two cases are not related with Clang.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black"><br>
At 2017-06-03 22:45:11, "Marcin Słowik" <<a href="mailto:slowikmarcin1992@gmail.com">slowikmarcin1992@gmail.com</a>> wrote:<br>
<br>
<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black">If i'm not mistaken, it is not a matter of LLVM IR nor LLVM backend, but rather LLVM frontend i.e. clang in this case.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black">Also, there is a slight semantic difference between those two cases:<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black">`}` is not a statement. `continue` is.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black">In the first case, `br` does not correspond to the `}` itself, but rather to a natural BB termination.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black">In the latter, `br` explicitly corresponds to the `continue`.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black">If you still wonder what is the difference, look at the IR in the third case: without any braces. Where would you expect the debug information to be?<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black">Cheers,<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black">Marcin<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black">2017-06-03 15:46 GMT+02:00 Frozen <<a href="mailto:bluechristlove@163.com" target="_blank">bluechristlove@163.com</a>>:<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black">Hi Marcin:<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black"> I don't expect stop the right brace } and expect stop at continue keyword statement. My question is continue keyword statement is the same as right brace }
statement in the LLVM IR except the !dbg!23 has different line number. I don't know how the LLVM backend distinguish it. <o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black"><br>
</span><span style="font-size:10.5pt;font-family:"MS Gothic";color:black">在</span><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black"> 2017-06-03 19:20:46</span><span style="font-size:10.5pt;font-family:"MS Gothic";color:black">，</span><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black">"Marcin
Słowik" <<a href="mailto:me@marandil.pl" target="_blank">me@marandil.pl</a>> </span>
<span style="font-size:10.5pt;font-family:"MS Gothic";color:black">写道：</span><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black"><br>
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<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black">On Jun 3, 2017 9:48 AM, "Frozen via llvm-dev" <<a href="mailto:llvm-dev@lists.llvm.org" target="_blank">llvm-dev@lists.llvm.org</a>> wrote:<o:p></o:p></span></p>
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<p class="MsoNormal"><b><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black">Why continue keyword can be emitted but right brace won't be emitted, and debbuger can stop at continue keyword statement but won't stop at right brace statement?</span></b><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black"><o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black">Simply because continue keyword is a part of the AST, while '}' is not. <o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black">And you don't break on "natural" terminators. Also, would you expect a different behavior between:<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black">for(i=0;i<N;++i)<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black"> doStuff();<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black">And:<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black">for(i=0;i<N;++i) {<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black"> doStuff();<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black">} <o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black">While they should be identical on AST level? <o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black">Cheers, <o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black">Marcin <o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:"Arial","sans-serif";color:black">Marcin Słowik<o:p></o:p></span></p>
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