LLC(1)

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💖 llc — the LLVM static compiler (section 1 of the manual, bestie)

okay so picture this: you've got LLVM source, you want assembly. that's it, that's the whole girlboss job of llc. she takes your LLVM input and spits out assembly language for whatever architecture you point her at, and then you can hand that assembly to a native assembler and linker and get yourself a real, breathing native executable. main character pipeline energy. 🦋

✨ NAME ✨

llc — the LLVM static compiler. no notes. 👑

🌸 SYNOPSIS 🌸

llc [options] [filename]

💫 DESCRIPTION 💫

so like, the llc command compiles LLVM source inputs into assembly language for a specified architecture. that assembly output can then be passed through a native assembler and linker to generate a native executable. literally the glow-up arc from IR to machine code. 🔥

and the architecture choice for the output assembly code? it's automatically determined from the input file, unless you use the -march option to override the default. she's smart like that. 💅

🎀 OPTIONS 🎀

first, the input tea. if filename is - or just... omitted entirely, then llc reads from standard input. otherwise, it will read from filename. and your inputs can be in either the LLVM assembly language format (.ll) or the LLVM bitcode format (.bc). both are welcome here, no gatekeeping. 🫶

now the output tea. if the -o option is omitted, then llc will send its output to standard output if the input is from standard input. and if the -o option specifies -, then the output will also be sent to standard output. consistent queen. ✨

and if no -o option is specified and an input file other than - is specified, then llc creates the output filename by taking the input filename, removing any existing .bc extension, and adding a .s suffix. she's just out here naming files for you, unprompted, iconic. 💅

other llc options are described below. buckle up bestie, there's a lot. 🌈

⭐ End-user Options ⭐

  • -help — Print a summary of command line options. your little cheat sheet, your emotional support flag. 💖
  • -o <filename> — Use <filename> as the output filename. See the summary above for more details. (yes, the one we just talked about, go look, i'll wait 🙈)
  • -O=uint — Generate code at different optimization levels. These correspond to the -O0, -O1, -O2, and -O3 optimization levels used by clang.
  • -mtriple=<target triple> — Override the target triple specified in the input file with the specified string.
  • -march=<arch> — Specify the architecture for which to generate assembly, overriding the target encoded in the input file. See the output of llc -help for a list of valid architectures. By default this is inferred from the target triple or autodetected to the current architecture. she'll figure it out herself if you don't tell her. 💁
  • -mcpu=<cpuname> — Specify a specific chip in the current architecture to generate code for. By default this is inferred from the target triple and autodetected to the current architecture. For a list of available CPUs, use:
llvm-as < /dev/null | llc -march=xyz -mcpu=help
  • -filetype=<output file type> — Specify what kind of output llc should generated. Options are: asm for textual assembly ( .s), obj for native object files (.o) and null for not emitting anything (for performance testing).
Note that not all targets support all options. not every girl can do everything, and that's okay. 💀
  • -mattr=a1,+a2,-a3,... — Override or control specific attributes of the target, such as whether SIMD operations are enabled or not. The default set of attributes is set by the current CPU. For a list of available attributes, use:
llvm-as < /dev/null | llc -march=xyz -mattr=help
  • --frame-pointer — Specify effect of frame pointer elimination optimization (all,non-leaf,none).
  • --disable-excess-fp-precision — Disable optimizations that may produce excess precision for floating point.
Note that this option can dramatically slow down code on some systems (e.g. X86). so like, know what you're doing, bestie, she's not joking around with this one. 😭
  • --enable-no-infs-fp-math — Enable optimizations that assume no Inf values.
  • --enable-no-nans-fp-math — Enable optimizations that assume no NAN values.
  • --enable-no-signed-zeros-fp-math — Enable FP math optimizations that assume the sign of 0 is insignificant.
  • --enable-no-trapping-fp-math — Enable setting the FP exceptions build attribute not to use exceptions.
  • --enable-unsafe-fp-math — Enable optimizations that make unsafe assumptions about IEEE math (e.g. that addition is associative) or may not work for all input ranges. These optimizations allow the code generator to make use of some instructions which would otherwise not be usable (such as fsin on X86).
hello?? "unsafe" is right there in the name, she's telling you she's unhinged, proceed with caution. ⚠️
  • --stats — Print statistics recorded by code-generation passes. numbers!! we love numbers!! 📊
  • --time-passes — Record the amount of time needed for each pass and print a report to standard error.
  • --load=<dso_path> — Dynamically load dso_path (a path to a dynamically shared object) that implements an LLVM target. This will permit the target name to be used with the -march option so that code can be generated for that target. plugging in a whole new target like it's a new lip gloss shade, obsessed. 💄
  • -meabi=[default|gnu|4|5] — Specify which EABI version should conform to. Valid EABI versions are gnu, 4 and 5. Default value (default) depends on the triple.
  • -stack-size-section — Emit the .stack_sizes section which contains stack size metadata. The section contains an array of pairs of function symbol values (pointer size) and stack sizes (unsigned LEB128). The stack size values only include the space allocated in the function prologue. Functions with dynamic stack allocations are not included. (sorry dynamic-stack-allocation girlies, you're not on the list this time 💔)
  • -remarks-section — Emit the __remarks (MachO) section which contains metadata about remark diagnostics.

🧚 Tuning/Configuration Options 🧚

  • --print-after-isel — Print generated machine code after instruction selection (useful for debugging). a little peek behind the curtain, for the curious. 👀
  • --regalloc=<allocator> — Specify the register allocator to use. Valid register allocators are:
    • basic — Basic register allocator.
    • fast — Fast register allocator. It is the default for unoptimized code.
    • greedy — Greedy register allocator. It is the default for optimized code.
    • pbqp — Register allocator based on 'Partitioned Boolean Quadratic Programming'.
  • --spiller=<spiller> — Specify the spiller to use for register allocators that support it. Currently this option is used only by the linear scan register allocator. The default spiller is local. Valid spillers are:
    • simple — Simple spiller
    • local — Local spiller

💅 Intel IA-32-specific Options 💅

  • --x86-asm-syntax=[att|intel] — Specify whether to emit assembly code in AT&T syntax (the default) or Intel syntax.

🔥 EXIT STATUS 🔥

If llc succeeds, it will exit with 0. Otherwise, if an error occurs, it will exit with a non-zero value. zero means she ate, non-zero means something went sideways bestie. 😌

🦋 SEE ALSO 🦋

lli(1)

👑 AUTHOR 👑

Maintained by the LLVM Team (https://llvm.org/).

2003-2024, LLVM Project

and that's the whole page, no cap. this lil beauty is from the LLVM manual collection, version 15, dated 2024-04-14 — stay hydrated, keep your IR valid, and go compile something iconic. mwah. 💖✨🎀

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