| llvm-mca - LLVM Machine Code Analyzer |
| ===================================== |
| |
| SYNOPSIS |
| -------- |
| |
| :program:`llvm-mca` [*options*] [input] |
| |
| DESCRIPTION |
| ----------- |
| |
| :program:`llvm-mca` is a performance analysis tool that uses information |
| available in LLVM (e.g. scheduling models) to statically measure the performance |
| of machine code in a specific CPU. |
| |
| Performance is measured in terms of throughput as well as processor resource |
| consumption. The tool currently works for processors with an out-of-order |
| backend, for which there is a scheduling model available in LLVM. |
| |
| The main goal of this tool is not just to predict the performance of the code |
| when run on the target, but also help with diagnosing potential performance |
| issues. |
| |
| Given an assembly code sequence, llvm-mca estimates the IPC (Instructions Per |
| Cycle), as well as hardware resource pressure. The analysis and reporting style |
| were inspired by the IACA tool from Intel. |
| |
| OPTIONS |
| ------- |
| |
| If ``input`` is "``-``" or omitted, :program:`llvm-mca` reads from standard |
| input. Otherwise, it will read from the specified filename. |
| |
| If the :option:`-o` option is omitted, then :program:`llvm-mca` will send its output |
| to standard output if the input is from standard input. If the :option:`-o` |
| option specifies "``-``", then the output will also be sent to standard output. |
| |
| |
| .. option:: -help |
| |
| Print a summary of command line options. |
| |
| .. option:: -mtriple=<target triple> |
| |
| Specify a target triple string. |
| |
| .. option:: -march=<arch> |
| |
| Specify the architecture for which to analyze the code. It defaults to the |
| host default target. |
| |
| .. option:: -mcpu=<cpuname> |
| |
| Specify the processor for whic to run the analysis. |
| By default this defaults to a "generic" processor. It is not autodetected to |
| the current architecture. |
| |
| .. option:: -output-asm-variant=<variant id> |
| |
| Specify the output assembly variant for the report generated by the tool. |
| On x86, possible values are [0, 1]. A value of 0 (vic. 1) for this flag enables |
| the AT&T (vic. Intel) assembly format for the code printed out by the tool in |
| the analysis report. |
| |
| .. option:: -dispatch=<width> |
| |
| Specify a different dispatch width for the processor. The dispatch width |
| defaults to the 'IssueWidth' specified by the processor scheduling model. |
| If width is zero, then the default dispatch width is used. |
| |
| .. option:: -max-retire-per-cycle=<retire throughput> |
| |
| Specify the retire throughput (i.e. how many instructions can be retired by the |
| retire control unit every cycle). |
| |
| .. option:: -register-file-size=<size> |
| |
| Specify the size of the register file. When specified, this flag limits |
| how many temporary registers are available for register renaming purposes. By |
| default, the number of temporary registers is unlimited. A value of zero for |
| this flag means "unlimited number of temporary registers". |
| |
| .. option:: -iterations=<number of iterations> |
| |
| Specify the number of iterations to run. If this flag is set to 0, then the |
| tool sets the number of iterations to a default value (i.e. 70). |
| |
| .. option:: -noalias=<bool> |
| |
| If set, the tool assumes that loads and stores don't alias. This is the |
| default behavior. |
| |
| .. option:: -lqueue=<load queue size> |
| |
| Specify the size of the load queue in the load/store unit emulated by the tool. |
| By default, the tool assumes an unbound number of entries in the load queue. |
| A value of zero for this flag is ignored, and the default load queue size is |
| used instead. |
| |
| .. option:: -squeue=<store queue size> |
| |
| Specify the size of the store queue in the load/store unit emulated by the |
| tool. By default, the tool assumes an unbound number of entries in the store |
| queue. A value of zero for this flag is ignored, and the default store queue |
| size is used instead. |
| |
| .. option:: -verbose |
| |
| Enable verbose output. In particular, this flag enables a number of extra |
| statistics and performance counters for the dispatch logic, the reorder |
| buffer, the retire control unit and the register file. |
| |
| .. option:: -timeline |
| |
| Enable the timeline view. |
| |
| .. option:: -timeline-max-iterations=<iterations> |
| |
| Limit the number of iterations to print in the timeline view. By default, the |
| timeline view prints information for up to 10 iterations. |
| |
| .. option:: -timeline-max-cycles=<cycles> |
| |
| Limit the number of cycles in the timeline view. By default, the number of |
| cycles is set to 80. |
| |
| |
| EXIT STATUS |
| ----------- |
| |
| :program:`llvm-mca` returns 0 on success. Otherwise, an error message is printed |
| to standard error, and the tool returns 1. |
| |