crates/stdsimd-test/src/lib.rs

//! Runtime support needed for testing the stdsimd crate.
//!
//! This basically just disassembles the current executable and then parses the
//! output once globally and then provides the `assert` function which makes
//! assertions about the disassembly of a function.

#![cfg_attr(
    feature = "cargo-clippy",
    allow(missing_docs_in_private_items, print_stdout)
)]

extern crate assert_instr_macro;
extern crate backtrace;
extern crate cc;
#[macro_use]
extern crate lazy_static;
extern crate rustc_demangle;
extern crate simd_test_macro;
#[macro_use]
extern crate cfg_if;

pub use assert_instr_macro::*;
pub use simd_test_macro::*;
use std::{collections::HashMap, env, str};

cfg_if! {
    if #[cfg(target_arch = "wasm32")] {
        extern crate wasm_bindgen;
        pub mod wasm;
        use wasm::disassemble_myself;
    } else {
        mod disassembly;
        use disassembly::disassemble_myself;
    }
}

lazy_static! {
    static ref DISASSEMBLY: HashMap<String, Vec<Function>> =
        disassemble_myself();
}

struct Function {
    addr: Option<usize>,
    instrs: Vec<Instruction>,
}

struct Instruction {
    parts: Vec<String>,
}

fn normalize(symbol: &str) -> String {
    let symbol = rustc_demangle::demangle(symbol).to_string();
    match symbol.rfind("::h") {
        Some(i) => symbol[..i].to_string(),
        None => symbol.to_string(),
    }
}

/// Main entry point for this crate, called by the `#[assert_instr]` macro.
///
/// This asserts that the function at `fnptr` contains the instruction
/// `expected` provided.
pub fn assert(fnptr: usize, fnname: &str, expected: &str) {
    let mut fnname = fnname.to_string();
    let functions = get_functions(fnptr, &mut fnname);
    assert_eq!(functions.len(), 1);
    let function = &functions[0];

    let mut instrs = &function.instrs[..];
    while instrs.last().map_or(false, |s| s.parts == ["nop"]) {
        instrs = &instrs[..instrs.len() - 1];
    }

    // Look for `expected` as the first part of any instruction in this
    // function, returning if we do indeed find it.
    let mut found = false;
    for instr in instrs {
        // Gets the first instruction, e.g. tzcntl in tzcntl %rax,%rax
        if let Some(part) = instr.parts.get(0) {
            // Truncates the instruction with the length of the expected
            // instruction: tzcntl => tzcnt and compares that.
            if part.starts_with(expected) {
                found = true;
                break;
            }
        }
    }

    // Look for `call` instructions in the disassembly to detect whether
    // inlining failed: all intrinsics are `#[inline(always)]`, so
    // calling one intrinsic from another should not generate `call`
    // instructions.
    let mut inlining_failed = false;
    for (i, instr) in instrs.iter().enumerate() {
        let part = match instr.parts.get(0) {
            Some(part) => part,
            None => continue,
        };
        if !part.contains("call") {
            continue;
        }

        // On 32-bit x86 position independent code will call itself and be
        // immediately followed by a `pop` to learn about the current address.
        // Let's not take that into account when considering whether a function
        // failed inlining something.
        let followed_by_pop = function
            .instrs
            .get(i + 1)
            .and_then(|i| i.parts.get(0))
            .map_or(false, |s| s.contains("pop"));
        if followed_by_pop && cfg!(target_arch = "x86") {
            continue;
        }

        inlining_failed = true;
        break;
    }

    let instruction_limit = std::env::var("STDSIMD_ASSERT_INSTR_LIMIT")
        .map(|v| v.parse().unwrap())
        .unwrap_or_else(|_| match expected {
            // cpuid returns a pretty big aggregate structure so exempt it from
            // the slightly more restrictive 22 instructions below
            "cpuid" => 30,

            // Apparently on Windows LLVM generates a bunch of saves/restores
            // of xmm registers around these intstructions which
            // blows the 20 limit below. As it seems dictates by
            // Windows's abi (I guess?) we probably can't do much
            // about it...
            "vzeroall" | "vzeroupper" if cfg!(windows) => 30,

            // Intrinsics using `cvtpi2ps` are typically "composites" and in
            // some cases exceed the limit.
            "cvtpi2ps" => 25,

            // Original limit was 20 instructions, but ARM DSP Intrinsics are
            // exactly 20 instructions long. So bump the limit to 22 instead of
            // adding here a long list of exceptions.
            _ => 22,
        });
    let probably_only_one_instruction = instrs.len() < instruction_limit;

    if found && probably_only_one_instruction && !inlining_failed {
        return;
    }

    // Help debug by printing out the found disassembly, and then panic as we
    // didn't find the instruction.
    println!("disassembly for {}: ", fnname,);
    for (i, instr) in instrs.iter().enumerate() {
        let mut s = format!("\t{:2}: ", i);
        for part in &instr.parts {
            s.push_str(part);
            s.push_str(" ");
        }
        println!("{}", s);
    }

    if !found {
        panic!(
            "failed to find instruction `{}` in the disassembly",
            expected
        );
    } else if !probably_only_one_instruction {
        panic!(
            "instruction found, but the disassembly contains too many \
             instructions: #instructions = {} >= {} (limit)",
            instrs.len(),
            instruction_limit
        );
    } else if inlining_failed {
        panic!(
            "instruction found, but the disassembly contains `call` \
             instructions, which hint that inlining failed"
        );
    }
}

fn get_functions(fnptr: usize, fnname: &mut String) -> &'static [Function] {
    // Translate this function pointer to a symbolic name that we'd have found
    // in the disassembly.
    let mut sym = None;
    backtrace::resolve(fnptr as *mut _, |name| {
        sym = name.name().and_then(|s| s.as_str()).map(normalize);
    });

    if let Some(sym) = &sym {
        if let Some(s) = DISASSEMBLY.get(sym) {
            *fnname = sym.to_string();
            return s;
        }
    }

    let exact_match = DISASSEMBLY
        .iter()
        .find(|(_, list)| list.iter().any(|f| f.addr == Some(fnptr)));
    if let Some((name, list)) = exact_match {
        *fnname = name.to_string();
        return list;
    }

    if let Some(sym) = sym {
        println!("assumed symbol name: `{}`", sym);
    }
    println!("maybe related functions");
    for f in DISASSEMBLY.keys().filter(|k| k.contains(&**fnname)) {
        println!("\t- {}", f);
    }
    panic!("failed to find disassembly of {:#x} ({})", fnptr, fnname);
}

pub fn assert_skip_test_ok(name: &str) {
    if env::var("STDSIMD_TEST_EVERYTHING").is_err() {
        return;
    }
    panic!("skipped test `{}` when it shouldn't be skipped", name);
}

// See comment in `assert-instr-macro` crate for why this exists
pub static mut _DONT_DEDUP: &'static str = "";