cranelift_codegen/isa/
call_conv.rs

1use crate::ir::Type;
2use crate::ir::types;
3use crate::settings::{self, LibcallCallConv};
4use core::fmt;
5use core::str;
6use target_lexicon::{CallingConvention, Triple};
7
8#[cfg(feature = "enable-serde")]
9use serde_derive::{Deserialize, Serialize};
10
11/// Calling convention identifiers.
12#[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
13#[cfg_attr(feature = "enable-serde", derive(Serialize, Deserialize))]
14pub enum CallConv {
15    /// Best performance, not ABI-stable.
16    Fast,
17    /// Smallest caller code size, not ABI-stable.
18    Cold,
19    /// Supports tail calls, not ABI-stable except for exception
20    /// payload registers.
21    ///
22    /// On exception resume, a caller to a `tail`-convention function
23    /// assumes that the exception payload values are in the following
24    /// registers (per platform):
25    /// - x86-64: rax, rdx
26    /// - aarch64: x0, x1
27    /// - riscv64: a0, a1
28    /// - pulley{32,64}: x0, x1
29    //
30    // Currently, this is basically sys-v except that callees pop stack
31    // arguments, rather than callers. Expected to change even more in the
32    // future, however!
33    Tail,
34    /// System V-style convention used on many platforms.
35    SystemV,
36    /// Windows "fastcall" convention, also used for x64 and ARM.
37    WindowsFastcall,
38    /// Mac aarch64 calling convention, which is a tweaked aarch64 ABI.
39    AppleAarch64,
40    /// Specialized convention for the probestack function.
41    Probestack,
42    /// The winch calling convention, not ABI-stable.
43    ///
44    /// The main difference to SystemV is that the winch calling convention
45    /// defines no callee-save registers, and restricts the number of return
46    /// registers to one integer, and one floating point.
47    Winch,
48    /// Calling convention for patchable-call instructions.
49    ///
50    /// This is designed for a very specific need: we want a *single*
51    /// call instruction at our callsite, with no other setup, and we
52    /// don't want any registers clobbered. This allows patchable
53    /// callsites to be as unobtrusive as possible.
54    ///
55    /// The ABI is based on the native register-argument ABI on each
56    /// respective platform, but puts severe restrictions on allowable
57    /// signatures: only up to four arguments of integer type, and no
58    /// return values. It does not support tail-calls, and disallows
59    /// any extension modes on arguments.
60    ///
61    /// The ABI specifies that *no* registers, not even argument
62    /// registers, are clobbered. This is pretty unique: it means that
63    /// the call instruction will constrain regalloc to have any args
64    /// in the right registers, but those registers will be preserved,
65    /// so multiple patchable callsites can reuse those values. This
66    /// further reduces the cost of the callsites.
67    Patchable,
68}
69
70impl CallConv {
71    /// Return the default calling convention for the given target triple.
72    pub fn triple_default(triple: &Triple) -> Self {
73        match triple.default_calling_convention() {
74            // Default to System V for unknown targets because most everything
75            // uses System V.
76            Ok(CallingConvention::SystemV) | Err(()) => Self::SystemV,
77            Ok(CallingConvention::AppleAarch64) => Self::AppleAarch64,
78            Ok(CallingConvention::WindowsFastcall) => Self::WindowsFastcall,
79            Ok(unimp) => unimplemented!("calling convention: {:?}", unimp),
80        }
81    }
82
83    /// Returns the calling convention used for libcalls according to the current flags.
84    pub fn for_libcall(flags: &settings::Flags, default_call_conv: CallConv) -> Self {
85        match flags.libcall_call_conv() {
86            LibcallCallConv::IsaDefault => default_call_conv,
87            LibcallCallConv::Fast => Self::Fast,
88            LibcallCallConv::Cold => Self::Cold,
89            LibcallCallConv::SystemV => Self::SystemV,
90            LibcallCallConv::WindowsFastcall => Self::WindowsFastcall,
91            LibcallCallConv::AppleAarch64 => Self::AppleAarch64,
92            LibcallCallConv::Probestack => Self::Probestack,
93        }
94    }
95
96    /// Does this calling convention support tail calls?
97    pub fn supports_tail_calls(&self) -> bool {
98        match self {
99            CallConv::Tail => true,
100            _ => false,
101        }
102    }
103
104    /// Does this calling convention support exceptions?
105    pub fn supports_exceptions(&self) -> bool {
106        match self {
107            CallConv::Tail | CallConv::SystemV | CallConv::Winch => true,
108            _ => false,
109        }
110    }
111
112    /// What types do the exception payload value(s) have?
113    ///
114    /// Note that this function applies to the *callee* of a `try_call`
115    /// instruction. The calling convention of the callee may differ from the
116    /// caller, but the exceptional payload types available are defined by the
117    /// callee calling convention.
118    ///
119    /// Also note that individual backends are responsible for reporting
120    /// register destinations for exceptional types. Internally Cranelift
121    /// asserts that the backend supports the exact same number of register
122    /// destinations as this return value.
123    pub fn exception_payload_types(&self, pointer_ty: Type) -> &[Type] {
124        match self {
125            CallConv::Tail | CallConv::SystemV => match pointer_ty {
126                types::I32 => &[types::I32, types::I32],
127                types::I64 => &[types::I64, types::I64],
128                _ => unreachable!(),
129            },
130            _ => &[],
131        }
132    }
133}
134
135impl fmt::Display for CallConv {
136    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
137        f.write_str(match *self {
138            Self::Fast => "fast",
139            Self::Cold => "cold",
140            Self::Tail => "tail",
141            Self::SystemV => "system_v",
142            Self::WindowsFastcall => "windows_fastcall",
143            Self::AppleAarch64 => "apple_aarch64",
144            Self::Probestack => "probestack",
145            Self::Winch => "winch",
146            Self::Patchable => "patchable",
147        })
148    }
149}
150
151impl str::FromStr for CallConv {
152    type Err = ();
153    fn from_str(s: &str) -> Result<Self, Self::Err> {
154        match s {
155            "fast" => Ok(Self::Fast),
156            "cold" => Ok(Self::Cold),
157            "tail" => Ok(Self::Tail),
158            "system_v" => Ok(Self::SystemV),
159            "windows_fastcall" => Ok(Self::WindowsFastcall),
160            "apple_aarch64" => Ok(Self::AppleAarch64),
161            "probestack" => Ok(Self::Probestack),
162            "winch" => Ok(Self::Winch),
163            "patchable" => Ok(Self::Patchable),
164            _ => Err(()),
165        }
166    }
167}
cranelift_codegen/isa/call_conv.rs

cranelift_codegen/isa/
call_conv.rs
