llvm dev - Apr 2015 - [LLVMdev] Target-independent machine-code analysis pass on LLVM

I'm trying to build an analysis pass over LLVM target-independent machine
code.
However, I need the machine code to be "as close to its future
target-specific code
as possible". As far as I understand the LLVM backend infrastructure,
the following applies:

- the LLVM IR abstracts the input code, allowing for many analysis and
optimization
  passes to take place;
- after that, a series of passes converts the IR representation into other
temporary
  structures, by taking target-specific decisions;
- finally, at the very beginning of code emission, there are
MachineFunctions,
  i.e., CFGs composed of MachineBasicBlocks (sequences of MachineInstrs);
- during code emission, MachineInstrs are converted into MCInsts, which are
later
  emitted as either target-specific assembly or binary object.

Since my goal is to deal with target-independent code, I must not write a
pass
to be executed by a single target-specific module. Yet, I have not found
how to
properly add a pass just before code emission.

As a workaround, I've added a stub in file:

    ~/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cppAsmPrinter.cpp

to call my analysis method over MachineFunctions. Despite the fact that it
does work,
I'd like to know if is there any elegant/correct way to do such analysis.

Notice my pass simply analyzes such structures, thus not modifying any of
them.
Also, it simply works because every target-specific code-emission module
inherits
from LLMV::AsmPrinter, which means I have my analysis called upon
any target-specific compilation (with llc -march=... input.bc).

Any ideas/suggestions on how to implement such analysis without resorting
to adding stubs/function calls on the AsmPrinter?


Regards!
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Is LLVMTargetMachine::addPassesToEmitFile() in
lib/CodeGen/LLVMTargetMachine.cpp before the AsmPrinter pass late enough
for your pass?

On Sat, Apr 25, 2015 at 5:50 AM, Rubens Emilio <rubenseam at gmail.com>
wrote:
> I'm trying to build an analysis pass over LLVM target-independent
machine
> code.
> However, I need the machine code to be "as close to its future
> target-specific code
> as possible". As far as I understand the LLVM backend infrastructure,
> the following applies:
>
> - the LLVM IR abstracts the input code, allowing for many analysis and
> optimization
>   passes to take place;
> - after that, a series of passes converts the IR representation into other
> temporary
>   structures, by taking target-specific decisions;
> - finally, at the very beginning of code emission, there are
> MachineFunctions,
>   i.e., CFGs composed of MachineBasicBlocks (sequences of MachineInstrs);
> - during code emission, MachineInstrs are converted into MCInsts, which
> are later
>   emitted as either target-specific assembly or binary object.
>
> Since my goal is to deal with target-independent code, I must not write a
> pass
> to be executed by a single target-specific module. Yet, I have not found
> how to
> properly add a pass just before code emission.
>
> As a workaround, I've added a stub in file:
>
>     ~/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cppAsmPrinter.cpp
>
> to call my analysis method over MachineFunctions. Despite the fact that it
> does work,
> I'd like to know if is there any elegant/correct way to do such
analysis.
>
> Notice my pass simply analyzes such structures, thus not modifying any of
> them.
> Also, it simply works because every target-specific code-emission module
> inherits
> from LLMV::AsmPrinter, which means I have my analysis called upon
> any target-specific compilation (with llc -march=... input.bc).
>
> Any ideas/suggestions on how to implement such analysis without resorting
> to adding stubs/function calls on the AsmPrinter?
>
>
> Regards!
>
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>
>
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