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<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>After a bunch more investigate, I’ve
seem to have figured out what is going on here. The MachineFunction holds a
vector of MachineBasicBlocks and it is this vector that is traversed by the MachineFunction
iterator when printing out instructions. The problem is occurring when a
modification to the CFG moves around so that the ordering of them is different.
Even if the pred/succ blocks are modified, their position in the MBBNumbering
vector does not change. This causes the CFG graph and the MachineFunction
vector to become out of sync causing all sorts of issues with code generation. (i.e.
having my return block being generated in the middle of a loop).<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>I figured that sorting the vector based on
the block id’s would fix this issue, but the constructor required to sort
correctly is marked as private. <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>So, my basic need is this. How do I
re-order the MachineBasicBlocks vector based on their Block ID numbers via the
current API(2.3)?<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
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<p class=MsoNormal><b><font size=2 face=Tahoma><span style='font-size:10.0pt;
font-family:Tahoma;font-weight:bold'>From:</span></font></b><font size=2
face=Tahoma><span style='font-size:10.0pt;font-family:Tahoma'>
llvmdev-bounces@cs.uiuc.edu [mailto:llvmdev-bounces@cs.uiuc.edu] <b><span
style='font-weight:bold'>On Behalf Of </span></b>Villmow, Micah<br>
<b><span style='font-weight:bold'>Sent:</span></b> Tuesday, October 14, 2008
10:59 AM<br>
<b><span style='font-weight:bold'>To:</span></b> LLVM Developers Mailing List<br>
<b><span style='font-weight:bold'>Subject:</span></b> Re: [LLVMdev] CFG
modifcations and code gen</span></font><o:p></o:p></p>
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<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Chris,<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'> I took a look at AnalyzeBranch and I
don’t see how it can solve my problem. The issue itself isn’t with
branching, as I can handle branches fairly well in my custom pass(see the
before and after dot files attached). I can take a bunch of branches and
construct high level control flow for my backend since I have no ability to do
goto/jump, only whileloop and ifs. So analyzing the branch’s isn’t
the problem. The problem comes with emit’ing the code. Even though
I’ve renumbered the blocks and re-ordered the CFG into a more sane
control flow. The code emitter still processes the blocks in the old order. So
instead of going from 0-5, it prints out the instructions in the order, 0, 1,
2, 5, 3, 4. This is the order that the old CFG is in, not the new one after
this pass is done.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>I’ve added this analysis pass as a
PreEmitPass, is this the correct location to implement this? Or should I be
implementing it earlier? Later?<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Thanks for any advice,<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
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<p class=MsoNormal><b><font size=2 face=Tahoma><span style='font-size:10.0pt;
font-family:Tahoma;font-weight:bold'>From:</span></font></b><font size=2
face=Tahoma><span style='font-size:10.0pt;font-family:Tahoma'> llvmdev-bounces@cs.uiuc.edu
[mailto:llvmdev-bounces@cs.uiuc.edu] <b><span style='font-weight:bold'>On
Behalf Of </span></b>Chris Lattner<br>
<b><span style='font-weight:bold'>Sent:</span></b> Tuesday, October 14, 2008
9:50 AM<br>
<b><span style='font-weight:bold'>To:</span></b> LLVM Developers Mailing List<br>
<b><span style='font-weight:bold'>Subject:</span></b> Re: [LLVMdev] CFG
modifcations and code gen</span></font><o:p></o:p></p>
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<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'><o:p> </o:p></span></font></p>
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<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>On Oct 14, 2008, at 9:16 AM, Villmow, Micah wrote:<o:p></o:p></span></font></p>
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<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>But, the branch folding pass, or whatever
passes are supposed to reorder the blocks based on the CFG, are not doing so in
this case. Otherwise there is no way that blocks 2 and 4 should be printing out
before blocks 3 & 5. Renumber blocks just seems to reorder the values based
on their pre-set block number, but when the CFG is modified these number should
modified also to follow the new ordering, which is not occurring.</span></font><font
color=black><span style='color:black'><o:p></o:p></span></font></p>
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<div></u1:smarttagtype></u1:smarttagtype></u1:smarttagtype></u1:smarttagtype>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'></span><o:p> </o:p></span></font></p>
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<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>Did you implement TargetInstrInfo::AnalyzeBranch for your target?
Check out the large comment above it in TargetInstrInfo.h<o:p></o:p></span></font></p>
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<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'><o:p> </o:p></span></font></p>
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<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>-Chris<o:p></o:p></span></font></p>
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