llvm-exegesis - LLVM Machine Instruction Benchmark

SYNOPSIS

llvm-exegesis [options]

DESCRIPTION

llvm-exegesis is a benchmarking tool that uses information available in LLVM to measure host machine instruction characteristics like latency or port decomposition.

Given an LLVM opcode name and a benchmarking mode, llvm-exegesis generates a code snippet that makes execution as serial (resp. as parallel) as possible so that we can measure the latency (resp. uop decomposition) of the instruction. The code snippet is jitted and executed on the host subtarget. The time taken (resp. resource usage) is measured using hardware performance counters. The result is printed out as YAML to the standard output.

The main goal of this tool is to automatically (in)validate the LLVM’s TableDef scheduling models.

OPTIONS

-help

Print a summary of command line options.

-opcode-index=<LLVM opcode index>

Specify the opcode to measure, by index. Either opcode-index or opcode-name must be set.

-opcode-name=<LLVM opcode name>

Specify the opcode to measure, by name. Either opcode-index or opcode-name must be set.

-benchmark-mode=[Latency|Uops]

Specify which characteristic of the opcode to measure.

-num-repetitions=<Number of repetition>

Specify the number of repetitions of the asm snippet. Higher values lead to more accurate measurements but lengthen the benchmark.

EXIT STATUS

llvm-exegesis returns 0 on success. Otherwise, an error message is printed to standard error, and the tool returns a non 0 value.