Code Annotations

The overhead of compiler-based instruction can be very high, particularly for code with high floating-point arithmetic intensity. We provide annotations as a method to control (and hopefully reduce) the instrumentation overhead.

When a particular code region is annotated, the instrumentation only occurs in the annotated region, instead of in the entire application. We provide two levels for annotations: function and basic block annotations.

When code is annotated, the FPC_ANNOTATED variable must be set.

Function Annotations

To annotate a function, add FPC_INSTRUMENT_FUNC macro to the definition of a function. For example:

FPC_INSTRUMENT_FUNC
double my_function(double *x, int size) {
  ...
  ...
} 

Basic Block Annotations

To annotate a basic block of code, add FPC_INSTRUMENT_BLOCK macro to the begininng of the target basic block. For example:

double my_function(double *x, int size) {
  // Annotated basic block
  FPC_INSTRUMENT_BLOCK;
  double tmp = x[0] + 1.23;
  x[1] = tmp / 2.0;
  
  // For loop
  for (int i=0; ...) {
    // This block is not annotated
    ...
  }
} 

These macros are defined in Runtime_cpu.h as:

#define FPC_INSTRUMENT_BLOCK __attribute__((annotate("_FPC_INSTRUMENT_BLOCK_"))) int _marker __attribute__((unused)) = 0;
#define FPC_INSTRUMENT_FUNC __attribute__((annotate("_FPC_INSTRUMENT_FUNCTION_")))