llvm dev - Apr 2013 - [LLVMdev] How to know if an instruction is "usable"

Thanks,
So, how do I check if a block dominates another one?


On 25 April 2013 11:59, Krzysztof Parzyszek <kparzysz at codeaurora.org>
wrote:
> On 4/25/2013 11:52 AM, Giacomo Tagliabue wrote:
>
>> Is there an easy way to know if, at a certain instruction, a certain
>> value is usable or not? i.e., I am sure that if i use that value i
don't
>> to get the error "Instruction does not dominate all uses!"
>>
>
> Check if the block containing the definition dominates the block where you
> want to use the value.  If this is the same block, the definition has to
> appear before the use.  This follows directly from the error message, so
> I'm not sure if this answers your question.  Use the dominator tree
> analysis to check the dominance.
>
> -Krzysztof
>
> --
> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted
> by The Linux Foundation
> ______________________________**_________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>
http://lists.cs.uiuc.edu/**mailman/listinfo/llvmdev<http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://lists.llvm.org/pipermail/llvm-dev/attachments/20130425/7801552d/attachment.html>

On 4/25/2013 12:06 PM, Giacomo Tagliabue wrote:
> Thanks,
> So, how do I check if a block dominates another one?
In IR use analysis DominatorTree from 
"include/llvm/Analysis/Dominators.h".  For machine instructions, use 
MachineDominatorTree
from "include/llvm/CodeGen/MachineDominators.h".

Both of them implement function "dominates" that takes two blocks 
(BasicBlock* or MachineBasicBlock*) and returns a boolean value 
indicating whether one dominates the other.  A block will always 
dominate itself, so this case needs to be handled separately to 
determine relative position between the def and the use instruction.

-Krzysztof

-- 
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, 
hosted by The Linux Foundation

Thanks! I checked that module. If I use dominates(const Instruction
*Def,const Instruction *User) it will automatically check everything, so I
don't have to handle the case with instructions in the same BB, right?
Thanks,
GT


On 25 April 2013 12:17, Krzysztof Parzyszek <kparzysz at codeaurora.org>
wrote:
> On 4/25/2013 12:06 PM, Giacomo Tagliabue wrote:
>
>> Thanks,
>> So, how do I check if a block dominates another one?
>>
>
> In IR use analysis DominatorTree from
"include/llvm/Analysis/**Dominators.h".
>  For machine instructions, use MachineDominatorTree
> from "include/llvm/CodeGen/**MachineDominators.h".
>
> Both of them implement function "dominates" that takes two blocks
> (BasicBlock* or MachineBasicBlock*) and returns a boolean value indicating
> whether one dominates the other.  A block will always dominate itself, so
> this case needs to be handled separately to determine relative position
> between the def and the use instruction.
>
>
> -Krzysztof
>
> --
> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted
> by The Linux Foundation
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://lists.llvm.org/pipermail/llvm-dev/attachments/20130425/0fa3d99d/attachment.html>