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