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e2bef9a902
Before this patch, the "BackendStatistics" view was responsible for printing the register file usage (as well as many other statistics). Now users can enable register file usage statistics using the command line flag `-register-file-stats`. By default, the tool doesn't print register file statistics. llvm-svn: 329083
154 lines
5.0 KiB
ReStructuredText
154 lines
5.0 KiB
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llvm-mca - LLVM Machine Code Analyzer
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=====================================
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SYNOPSIS
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--------
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:program:`llvm-mca` [*options*] [input]
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DESCRIPTION
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-----------
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:program:`llvm-mca` is a performance analysis tool that uses information
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available in LLVM (e.g. scheduling models) to statically measure the performance
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of machine code in a specific CPU.
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Performance is measured in terms of throughput as well as processor resource
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consumption. The tool currently works for processors with an out-of-order
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backend, for which there is a scheduling model available in LLVM.
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The main goal of this tool is not just to predict the performance of the code
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when run on the target, but also help with diagnosing potential performance
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issues.
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Given an assembly code sequence, llvm-mca estimates the IPC (Instructions Per
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Cycle), as well as hardware resource pressure. The analysis and reporting style
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were inspired by the IACA tool from Intel.
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OPTIONS
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-------
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If ``input`` is "``-``" or omitted, :program:`llvm-mca` reads from standard
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input. Otherwise, it will read from the specified filename.
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If the :option:`-o` option is omitted, then :program:`llvm-mca` will send its output
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to standard output if the input is from standard input. If the :option:`-o`
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option specifies "``-``", then the output will also be sent to standard output.
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.. option:: -help
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Print a summary of command line options.
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.. option:: -mtriple=<target triple>
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Specify a target triple string.
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.. option:: -march=<arch>
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Specify the architecture for which to analyze the code. It defaults to the
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host default target.
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.. option:: -mcpu=<cpuname>
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Specify the processor for whic to run the analysis.
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By default this defaults to a "generic" processor. It is not autodetected to
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the current architecture.
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.. option:: -output-asm-variant=<variant id>
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Specify the output assembly variant for the report generated by the tool.
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On x86, possible values are [0, 1]. A value of 0 (vic. 1) for this flag enables
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the AT&T (vic. Intel) assembly format for the code printed out by the tool in
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the analysis report.
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.. option:: -dispatch=<width>
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Specify a different dispatch width for the processor. The dispatch width
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defaults to the 'IssueWidth' specified by the processor scheduling model.
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If width is zero, then the default dispatch width is used.
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.. option:: -max-retire-per-cycle=<retire throughput>
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Specify the retire throughput (i.e. how many instructions can be retired by the
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retire control unit every cycle).
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.. option:: -register-file-size=<size>
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Specify the size of the register file. When specified, this flag limits
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how many temporary registers are available for register renaming purposes. By
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default, the number of temporary registers is unlimited. A value of zero for
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this flag means "unlimited number of temporary registers".
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.. option:: -iterations=<number of iterations>
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Specify the number of iterations to run. If this flag is set to 0, then the
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tool sets the number of iterations to a default value (i.e. 70).
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.. option:: -noalias=<bool>
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If set, the tool assumes that loads and stores don't alias. This is the
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default behavior.
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.. option:: -lqueue=<load queue size>
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Specify the size of the load queue in the load/store unit emulated by the tool.
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By default, the tool assumes an unbound number of entries in the load queue.
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A value of zero for this flag is ignored, and the default load queue size is
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used instead.
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.. option:: -squeue=<store queue size>
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Specify the size of the store queue in the load/store unit emulated by the
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tool. By default, the tool assumes an unbound number of entries in the store
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queue. A value of zero for this flag is ignored, and the default store queue
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size is used instead.
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.. option:: -verbose
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Enable verbose output. In particular, this flag enables a number of extra
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statistics and performance counters for the dispatch logic, the reorder
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buffer, the retire control unit and the register file.
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.. option:: -timeline
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Enable the timeline view.
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.. option:: -timeline-max-iterations=<iterations>
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Limit the number of iterations to print in the timeline view. By default, the
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timeline view prints information for up to 10 iterations.
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.. option:: -timeline-max-cycles=<cycles>
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Limit the number of cycles in the timeline view. By default, the number of
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cycles is set to 80.
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.. option:: -resource-pressure
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Enable the resource pressure view. This is enabled by default.
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.. option:: -register-file-stats
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Enable register file usage statistics.
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.. option:: -instruction-info
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Enable the instruction info view. This is enabled by default.
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.. option:: -instruction-tables
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Prints resource pressure information based on the static information
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available from the processor model. This differs from the resource pressure
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view because it doesn't require that the code is simulated. It instead prints
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the theoretical uniform distribution of resource pressure for every
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instruction in sequence.
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EXIT STATUS
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-----------
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:program:`llvm-mca` returns 0 on success. Otherwise, an error message is printed
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to standard error, and the tool returns 1.
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