[PATCH] D44892: Call JIT notifiers only after code sections are ready.

[Andres Freund via Phabricator via llvm-commits]

anarazel created this revision.
Herald added subscribers: llvm-commits, mgorny.

Previously JIT notifiers were called before relocations were
performed (leading to ominious function call of "0"), and before
memory marked executable (confusing some profilers).

Move notifications to finalizeLoadedModules().

Add PerfJITEventListener for perf profiling support.

Given that the listener has no dependencies, it might be sensible to
enable it by default when running on linux.

I followed existing precedent in registering the listener by default
in lli, but I'm not sure that's a great idea?  I've had to disable it
for the remote MCJIT tests - the computed address is from the remote,
and I didn't see a way to get access to the actual code.

Example:

$ cat /tmp/expensive_loop.c

bool stupid_isprime(uint64_t num)
{

  if (num == 2)
          return true;
  if (num < 1 || num % 2 == 0)
          return false;
  for(uint64_t i = 3; i < num / 2; i+= 2) {
          if (num % i == 0)
                  return false;
  }
  return true;

}

int main(int argc, char **argv)
{

  int numprimes = 0;
  
  for (uint64_t num = argc; num < 100000; num++)
  {
          if (stupid_isprime(num))
                  numprimes++;
  }
  
  return numprimes;

}

$ clang -ggdb -S -c -emit-llvm /tmp/expensive_loop.c -o
/tmp/expensive_loop.ll

$ perf record -o /tmp/perf.data -g -k 1 ./bin/lli -jit-kind=mcjit /tmp/expensive_loop.ll 1

$ perf inject --jit -i perf.data -o perf.jit.data

$ perf report -i perf.jit.data

- 92.59%  lli      jitted-5881-2.so                   [.] stupid_isprime stupid_isprime main llvm::MCJIT::runFunction llvm::ExecutionEngine::runFunctionAsMain main __libc_start_main 0x4bf6258d4c544155

+    0.85%  lli      ld-2.27.so                         [.] do_lookup_x

And line-level annotations also work:

       │              for(uint64_t i = 3; i < num / 2; i+= 2) {
       │1 30:   movq   $0x3,-0x18(%rbp)
  0.03 │1 38:   mov    -0x18(%rbp),%rax
  0.03 │        mov    -0x10(%rbp),%rcx
       │        shr    $0x1,%rcx
  3.63 │     ┌──cmp    %rcx,%rax
       │     ├──jae    6f
       │     │                if (num % i == 0)
  0.03 │     │  mov    -0x10(%rbp),%rax
       │     │  xor    %edx,%edx

89.00 │     │  divq   -0x18(%rbp)

       │     │  cmp    $0x0,%rdx
  0.22 │     │↓ jne    5f
       │     │                        return false;
       │     │  movb   $0x0,-0x1(%rbp)
       │     │↓ jmp    73
       │     │        }
  3.22 │1 5f:│↓ jmp    61
       │     │        for(uint64_t i = 3; i < num / 2; i+= 2) {


Repository:
  rL LLVM

https://reviews.llvm.org/D44892

Files:
  CMakeLists.txt
  docs/CMake.rst
  include/llvm/Config/config.h.cmake
  include/llvm/Config/llvm-config.h.cmake
  include/llvm/ExecutionEngine/JITEventListener.h
  lib/ExecutionEngine/CMakeLists.txt
  lib/ExecutionEngine/LLVMBuild.txt
  lib/ExecutionEngine/MCJIT/MCJIT.cpp
  lib/ExecutionEngine/MCJIT/MCJIT.h
  lib/ExecutionEngine/Orc/LLVMBuild.txt
  lib/ExecutionEngine/PerfJITEvents/CMakeLists.txt
  lib/ExecutionEngine/PerfJITEvents/LLVMBuild.txt
  lib/ExecutionEngine/PerfJITEvents/PerfJITEventListener.cpp
  tools/lli/CMakeLists.txt
  tools/lli/lli.cpp

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