program-markers inserts markers (as function calls) in C or C++ source code to enable differential testing for missed optimizations:
- Instrument a program.
- Compile it with two or more compilers (or compiler versions, or optimization levels, etc).
- For each output: the markers whose corresponding calls are still present in the generated assembly are alive, the remaining are dead.
- Differential testing: compare the sets of alive and dead markers across outputs.
There are two kinds of markers supported:
- DCE (Dead Code Elimination) Markers
- VR (Value Range) Markers
A DCEMarker tests if a compiler dead code eliminates a piece of code (basic block). For example,
if (Cond){
DCEMarker0_();
STMT0;
STMT1;
//...
}
If call DCEMarker0_(); is not present in the generated assembly code then the
compiler determined that Cond must always be false and therefore the body of
this if statement is dead.
A VRMarker tests if a compiler can determine subsets of the value ranges of variables, for example:
if (!(LB <= a and a <= UB))
VRMarker0_();
If call VRMarker0_(); is not present in the generated assembly code then the
compiler determined that a's value is always LB <= a <= UB. Currently only
integer variables are instrumented.
Prerequisites: cmake, make, clang/llvm 13/14.
mkdir build
cd build
cmake ..
cmake --build . [--parallel]
cmake --install . --prefix=/where/to/install/
cat test.c
int foo(int a) {
if (a == 0)
return 1;
else {
a = 5;
}
return a;
}
dead-instrument test.c --
cat test.c | clang-format
#if defined DisableDCEMarker0_
#define DCEMARKERMACRO0_ ;
#elif defined UnreachableDCEMarker0_
#define DCEMARKERMACRO0_ __builtin_unreachable();
#else
#define DCEMARKERMACRO0_ DCEMarker0_();
void DCEMarker0_(void);
#endif
#if defined DisableDCEMarker1_
#define DCEMARKERMACRO1_ ;
#elif defined UnreachableDCEMarker1_
#define DCEMARKERMACRO1_ __builtin_unreachable();
#else
#define DCEMARKERMACRO1_ DCEMarker1_();
void DCEMarker1_(void);
#endif
int foo(int a) {
if (a == 0)
{
DCEMARKERMACRO1_
return 1;
}
else {
DCEMARKERMACRO0_
a = 5;
}
return a;
}
Individual markers can be disabled or turned into unreachables (useful for helping the compiler optimize parts known to be dead):
gcc -E -P -DDisableDCEMarker0_ -DUnreachableDCEMarker1_ test.c | clang-format
int foo(int a) {
if (a == 0) {
__builtin_unreachable();
return 1;
} else {
;
a = 5;
}
return a;
}
Passing --ignore-functions-with-macros to program-markers will cause it to ignore any functions that contain macro expansions.
Value range markers can be emitted instead by using --mode=vr:
cat test.c
int foo(int a) {
if (a == 0)
return 1;
return 0;
}
program-markers --mode=vr test.c --
cat test.c | clang-format
#if defined DisableVRMarker0_
#define VRMARKERMACRO0_(VAR, TYPE)
#elif defined UnreachableVRMarker0_
#define VRMARKERMACRO0_(VAR, TYPE) \
if (!(VRMarkerLowerBound0_ <= (VAR) && (VAR) <= VRMarkerUpperBound0_)) \
__builtin_unreachable();
#else
#define VRMARKERMACRO0_(VAR, TYPE) \
if (!(VRMarkerLowerBound0_ <= (VAR) && (VAR) <= VRMarkerUpperBound0_)) \
VRMarker0_();
void VRMarker0_(void);
#endif
#ifndef VRMarkerLowerBound0_
#define VRMarkerLowerBound0_ 0
#endif
#ifndef VRMarkerUpperBound0_
#define VRMarkerUpperBound0_ 0
#endif
int foo(int a) {
VRMARKERMACRO0_(a,"int")
if (a == 0)
return 1;
return 0;
}
The ranges that each marker test can be adjucted via macros:
gcc -E -P -DVRMarkerLowerBound0_=-4 test.c | clang-format
void VRMarker0_(void);
int foo(int a) {
if (!(-4 <= (a) && (a) <= 0))
VRMarker0_();
if (a == 0)
return 1;
return 0;
}
pip install program-markers
To use the instrumenter in python import from program_markers.instrumenter import instrument_program: instrument_program(program: diopter.SourceProgram, ignore_functions_with_macros: bool) -> InstrumentedProgram.
./build_python_wheel_local.sh #this will build the current branch
pip install .
docker run --rm -e REVISION=REV -v `pwd`:/io theodort/manylinux-with-llvm:latest /io/build_python_wheel_docker.sh
This will build multiple wheels for REV with multiple python versions.
The output is stored in the wheelhouse directory.
The docker image is based on https://github.com/thetheodor/manylinux-with-llvm.
