[LLVMdev] Target-independent machine-code analysis pass on LLVM

[Rubens Emilio]

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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