<html><head><meta http-equiv="Content-Type" content="text/html charset=iso-8859-1"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><br><div><div>On Sep 17, 2012, at 9:13 AM, Tomas Minac <<a href="mailto:minac.tomas@gmail.com">minac.tomas@gmail.com</a>> wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite">
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<div class="moz-cite-prefix">Hi Andy,<br>
<br>
thank you for your respond,<br>
<br>
On 09/06/12 21:32, Andrew Trick wrote:<br>
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<div>On Sep 4, 2012, at 9:05 AM, Tomas Minac <<a moz-do-not-send="true" href="mailto:minac.tomas@gmail.com">minac.tomas@gmail.com</a>>
wrote:</div>
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Hello,<br>
<br>
I am member of research team on our Faculty of Information
Technology (university VUT in Brno Czech Republic). We use
LLVM for many projects and actually we want to create
system, which will be able compile and profile aplication
for VLIW processors in few iterations.<br>
We want to load profile information in 'opt' part of LLVM
and use it for create superblocks. Note, when superblocks
will be created, we want to use llc for our specials
backends.<br>
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I suggest looking at the problem upside-down. What optimization
do you need to enable on superblocks, and how will changing the
IR help? Any single predecessor blocks laid out sequentially
looks like a superblock to me. What do you gain by changing the
IR? Maybe you can write a self-contained MachineIR pass that
does the optimization you need, or extend an existing pass.</div>
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<div>-Andy</div>
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Our backend processor is VLIW, but we want our system to be platform
independent. That means, after this project we maybe used it for
specials risc processor or other VLIWs.<br>
We think superblock can has multiple outputs, so we want to somehow
put basic block together and not only these one, which has single
predecessor. The basic goal is create superblock by using branch
target expansion, loop peeling, loop unrolling (from article <a class="moz-txt-link-freetext" href="http://www.eecs.umich.edu/%7Emahlke/papers/1993/hwu_jsuper93.pdf">http://www.eecs.umich.edu/~mahlke/papers/1993/hwu_jsuper93.pdf</a>)
to get as big superblock as it will be possible. After, in llc will
be special scheduler and it will work with these superblocks.<br>
Finally, we decided to extend basic block class with information
(can be simply integer value) to which superblock basic block
belongs.<br></div></blockquote><div><br></div><div>Yes, you need to transform the CFG to form superblocks. No you don't need to extend the IR itself. You can implement a new Analysis pass that summarizes superblocks (e.g. which superblock does each block belong to). Although I'm not sure what that buys you over simply laying out the blocks in superblock order.</div><div>-Andy</div><div><br></div><blockquote type="cite"><div bgcolor="#FFFFFF" text="#000000"><blockquote cite="mid:CE09B65C-7B94-4C0E-AD1F-446C9009E625@apple.com" type="cite"><div>
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<div class="moz-forward-container"> *.ll -> opt
-> llc -> *.asm<br>
|<br>
profile information <br>
<br>
We are thinking about creating superblocks in two ways:<br>
1. Simply join basic blocks and branch instrunction in
the join point replace by some intrinsic instrunction.<br>
Example:<br>
<font face="monospace">define i32 @foo(i32 %a, i32 %b)
nounwind uwtable {<br>
entry:<br>
...<br>
br i1 %cond, label %if.then, label %if.else<br>
if.then: ;
preds = %entry<br>
...<br>
br label %if.end<br>
if.else: ;
preds = %entry<br>
...<br>
br label %if.end<br>
if.end: ;
preds = %if.else, %if.then<br>
...<br>
ret i32 %add7</font><br>
It will be transformed to:<br>
<br>
<font face="monospace">define i32 @foo(i32 %a, i32 %b)
nounwind uwtable {<br>
entry:<br>
...<br>
spec.instrinsic.instr.with.label.on.if.else()<br>
...<br>
br label %if.end<br>
if.else: ;
preds = %entry<br>
...<br>
br label %if.end<br>
if.end: ;
preds = %if.else, %if.then<br>
...<br>
ret i32 %add7</font><br>
<br>
2. Create class named SuperBlock, which will be very
similar to BasicBlock class and has vector of contained
BasicBlocks. Of course, in this case, we will have to
create MachineSuperBlock class, because we want to use
llc, how I noted above. Result can looks like that:<br>
Example:<br>
<font face="monospace">define i32 @foo(i32 %a, i32 %b)
nounwind uwtable {<br>
superblock.entry.start:<br>
entry:<br>
...<br>
br i1 %cond, label %if.then, label %if.else<br>
if.then: ;
preds = %entry<br>
...<br>
br label %if.end<br>
superblock.entry.end:<br>
superblock.if.else.start:<br>
if.else: ;
preds = %entry<br>
...<br>
br label %if.end<br>
</font><br>
<font face="monospace"><font face="monospace">superblock.if.else.end:<br>
superblock.if.end.start:<br>
</font> if.end:
; preds = %if.else, %if.then<br>
...<br>
ret i32 %add7</font><br>
<font face="monospace">superblock.if.end.end:</font><br>
<br>
What do you think which way will bring less problems for
additional processing with llc?<br>
<br>
I hope and looking for some more advices or any notes to
our drafts I will be thankfull.<br>
<br>
Regards,<br>
Tomas Minac<br>
<br>
<br>
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