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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Hello Dave,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">The problem is that this is not well-formed IR.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">A branch instruction is a terminator, and may only appear in the end of a basic block, never in the middle. You’ll need to split that basic block into two.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Michael<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>
<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""> llvmdev-bounces@cs.uiuc.edu [mailto:llvmdev-bounces@cs.uiuc.edu]
<b>On Behalf Of </b>Dave Pitsbawn<br>
<b>Sent:</b> Monday, April 06, 2015 06:54<br>
<b>To:</b> LLVM Developers Mailing List<br>
<b>Subject:</b> [LLVMdev] Unreachable br in IR but still seems to be executed<o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal" style="line-height:115%">I'm trying to implement a continue statement like in C<o:p></o:p></p>
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<p class="MsoNormal" style="line-height:115%"><o:p> </o:p></p>
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<p class="MsoNormal" style="line-height:115%"> if (i % 2 == 0)<br>
{<br>
i = i + 1;<br>
continue;<br>
}<br>
else<br>
{<br>
i = i + 1;<br>
}<o:p></o:p></p>
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<p class="MsoNormal" style="line-height:115%"><o:p> </o:p></p>
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<p class="MsoNormal" style="line-height:115%">My code generates IR like this, because of how I visit my AST, so when I encounter a continue or break statement I go and find the corresponding while.<o:p></o:p></p>
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<p class="MsoNormal" style="line-height:115%"><o:p> </o:p></p>
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<p class="MsoNormal" style="line-height:115%">I was hoping LLVM would do the right thing which is ignore the unreachable IR (br label %if.end). But it seems to somehow get to execute statements after my br<o:p></o:p></p>
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<p>I've marked it with "SHOULD NOT HAPPEN"<o:p></o:p></p>
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<p class="MsoNormal" style="line-height:115%">define i32 @Main() {<br>
entry:<br>
%i = alloca i32<br>
%loopCounter = alloca i32<br>
store i32 0, i32* %i<br>
store i32 0, i32* %loopCounter<br>
br label %while.cond<o:p></o:p></p>
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<p class="MsoNormal" style="line-height:115%">while.cond: ; preds = %if.end, %if.then, %<br>
entry<br>
%0 = load i32* %i<br>
%cmptmp = icmp slt i32 %0, 100<br>
br i1 %cmptmp, label %while.body, label %while.end<o:p></o:p></p>
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<p class="MsoNormal" style="line-height:115%">while.body: ; preds = %while.cond<br>
%1 = load i32* %i<br>
%modtmp = srem i32 %1, 2<br>
%cmptmp1 = icmp eq i32 %modtmp, 0<br>
br i1 %cmptmp1, label %if.then, label %if.else<o:p></o:p></p>
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<p class="MsoNormal" style="line-height:115%">while.end: ; preds = %while.cond<br>
%2 = load i32* %loopCounter<br>
ret i32 %2<o:p></o:p></p>
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<p class="MsoNormal" style="line-height:115%">if.then: ; preds = %while.body<br>
%3 = load i32* %i<br>
%add = add i32 %3, 1<br>
store i32 %add, i32* %i<br>
br label %while.cond<br>
%4 = load i32* %I <----------- SHOULD NOT HAPPEN<br>
%sub = sub i32 %4, 1<br>
store i32 %sub, i32* %i<br>
br label %if.end<o:p></o:p></p>
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<p class="MsoNormal" style="line-height:115%">if.else: ; preds = %while.body<br>
%5 = load i32* %i<br>
%add2 = add i32 %5, 1<br>
store i32 %add2, i32* %i<br>
br label %if.end<o:p></o:p></p>
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<p class="MsoNormal" style="line-height:115%">if.end: ; preds = %if.else, %if.then<br>
%6 = load i32* %loopCounter<br>
%add3 = add i32 %6, 1<br>
store i32 %add3, i32* %loopCounter<br>
br label %while.cond<o:p></o:p></p>
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<p class="MsoNormal" style="line-height:115%">after_ret: ; No predecessors!<br>
ret i32 0<br>
}<o:p></o:p></p>
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