Hi ,
I am trying to clone a BasicBlock. I want both to co-exist and I have introduced
a conditional branch to the original or the cloned BB.
I tried mapping the original instruction and the clone as below :
Instruction *NewInst = II->clone();
if (II->hasName())
NewInst->setName(II->getName());
NewBB->getInstList().push_back(NewInst);
ValueMap[II] = NewInst;
what I got from this is ,
→ eventhough I have set the same name , a new name is set for the clone.
original :
%CS1 = call fastcc int %add( int %tmp.5, int %tmp.6 ) ; [#uses=1]
clone :
%CS11 = call fastcc int %add( int %tmp.5, int %tmp.6 ) ; [#uses=1]
→ the verifier gives the following error
Instruction does not dominate all uses!
&n! bsp; for the original instruction.
Is it possible to have the instructions in the clone to have the same name
as the original BB ?
Is it possible to make the uses of the original instruction to be the
uses of the cloned instruction at the same time ?
What makes the above error ?
Is it because of SSA ?
I am trying to clone a BasicBlock. I want both to co-exist and I have introduced
a conditional branch to the original or the cloned BB.
I tried mapping the original instruction and the clone as below :
Instruction *NewInst = II->clone();
if (II->hasName())
NewInst->setName(II->getName());
NewBB->getInstList().push_back(NewInst);
ValueMap[II] = NewInst;
what I got from this is ,
--> eventhough I have set the same name , a new name is set for the clone.
original :
%CS1 = call fastcc int %add( int %tmp.5, int %tmp.6 ) ; <int> [#uses=1]
clone :
%CS11 = call fastcc int %add( int %tmp.5, int %tmp.6 ) ; <int> [#uses=1]
--> the verifier gives the following error
Instruction does not dominate all uses!
for the original instruction.
Is it possible to have the instructions in the clone to have the same name
as the original BB ?
No. Names must be unique.
Is it possible to make the uses of the original instruction to be the
uses of the cloned instruction at the same time ?
No. You need to clone all the uses and have them use the cloned def. Then depending upon your CFG you will probably need a phi node if the two paths merge back together.
What makes the above error ?
Is it because of SSA ?
Yes. This means that you defined an instruction in a basicblock that does not dominate all uses. This is a property of SSA.
Hi ,
I am trying to clone a BasicBlock. I want both to co-exist and I have
introduced
a conditional branch to the original or the cloned BB.
I have a pass I haven't commited that does just this. Well, it does so
to implement Arnold and Ryder style profiling. I can send you a copy of
that if you want (I hope to commit it soon once it is cleaned up some).
Your best bet is to run reg2mem, which removes most live values by
placing them in memory. the only live values that remain after that
pass are the allocas for the old registers and values from loads in the
predecessors of phi nodes to those phi nodes. This makes it much easier
to maintain SSA form (as there is only one type of simple live value you
have to worry about). It is also possible to remove the phi nodes
completely with a bit more transform, but that wasn't desirable in my
case, so I didn't, but you could easily extend the pass to do so.
(just for reference, my code clones all BB in a function and the CFG,
then takes backedges and interconnects the backedges of the original and
cloned versions, adding conditional branches at those join points.)
Hello Andrew ,
Yes , I have missed the phi node since my paths merge together. I’ll try this out.
I am implementing a timer based profiling scheme and hope your code will be useful
for me. Please send me a copy of your code.
Hello Andrew ,
Yes , I have missed the phi node since my paths merge together. I'll
try this out.
I am implementing a timer based profiling scheme and hope your code
will be useful
for me. Please send me a copy of your code.
I have commited an Arnold and Ryder style random sampling framework
(check out lib/Transforms/Instrumentation/RSProfiling.cpp). Two of the
methods use a global counter to choose when to profiler. It is quite
possible that this framework does exactly what you want.
I will be cleaning up the code and adding some docs in the next few
days.