AArch64CallingConv.td [plain text]
//==-- AArch64CallingConv.td - Calling Conventions for ARM ----*- tblgen -*-==//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
// This describes the calling conventions for AArch64 architecture.
//===----------------------------------------------------------------------===//
// The AArch64 Procedure Call Standard is unfortunately specified at a slightly
// higher level of abstraction than LLVM's target interface presents. In
// particular, it refers (like other ABIs, in fact) directly to
// structs. However, generic LLVM code takes the liberty of lowering structure
// arguments to the component fields before we see them.
//
// As a result, the obvious direct map from LLVM IR to PCS concepts can't be
// implemented, so the goals of this calling convention are, in decreasing
// priority order:
// 1. Expose *some* way to express the concepts required to implement the
// generic PCS from a front-end.
// 2. Provide a sane ABI for pure LLVM.
// 3. Follow the generic PCS as closely as is naturally possible.
//
// The suggested front-end implementation of PCS features is:
// * Integer, float and vector arguments of all sizes which end up in
// registers are passed and returned via the natural LLVM type.
// * Structure arguments with size <= 16 bytes are passed and returned in
// registers as similar integer or composite types. For example:
// [1 x i64], [2 x i64] or [1 x i128] (if alignment 16 needed).
// * HFAs in registers follow rules similar to small structs: appropriate
// composite types.
// * Structure arguments with size > 16 bytes are passed via a pointer,
// handled completely by the front-end.
// * Structure return values > 16 bytes via an sret pointer argument.
// * Other stack-based arguments (not large structs) are passed using byval
// pointers. Padding arguments are added beforehand to guarantee a large
// struct doesn't later use integer registers.
//
// N.b. this means that it is the front-end's responsibility (if it cares about
// PCS compliance) to check whether enough registers are available for an
// argument when deciding how to pass it.
class CCIfAlign<int Align, CCAction A>:
CCIf<"ArgFlags.getOrigAlign() == " # Align, A>;
def CC_A64_APCS : CallingConv<[
// SRet is an LLVM-specific concept, so it takes precedence over general ABI
// concerns. However, this rule will be used by C/C++ frontends to implement
// structure return.
CCIfSRet<CCAssignToReg<[X8]>>,
// Put ByVal arguments directly on the stack. Minimum size and alignment of a
// slot is 64-bit.
CCIfByVal<CCPassByVal<8, 8>>,
// Canonicalise the various types that live in different floating-point
// registers. This makes sense because the PCS does not distinguish Short
// Vectors and Floating-point types.
CCIfType<[v1i16, v2i8], CCBitConvertToType<f16>>,
CCIfType<[v1i32, v4i8, v2i16], CCBitConvertToType<f32>>,
CCIfType<[v8i8, v4i16, v2i32, v2f32, v1i64, v1f64], CCBitConvertToType<f64>>,
CCIfType<[v16i8, v8i16, v4i32, v2i64, v4f32, v2f64],
CCBitConvertToType<f128>>,
// PCS: "C.1: If the argument is a Half-, Single-, Double- or Quad- precision
// Floating-point or Short Vector Type and the NSRN is less than 8, then the
// argument is allocated to the least significant bits of register
// v[NSRN]. The NSRN is incremented by one. The argument has now been
// allocated."
CCIfType<[v1i8], CCAssignToReg<[B0, B1, B2, B3, B4, B5, B6, B7]>>,
CCIfType<[f16], CCAssignToReg<[H0, H1, H2, H3, H4, H5, H6, H7]>>,
CCIfType<[f32], CCAssignToReg<[S0, S1, S2, S3, S4, S5, S6, S7]>>,
CCIfType<[f64], CCAssignToReg<[D0, D1, D2, D3, D4, D5, D6, D7]>>,
CCIfType<[f128], CCAssignToReg<[Q0, Q1, Q2, Q3, Q4, Q5, Q6, Q7]>>,
// PCS: "C.2: If the argument is an HFA and there are sufficient unallocated
// SIMD and Floating-point registers (NSRN - number of elements < 8), then the
// argument is allocated to SIMD and Floating-point registers (with one
// register per element of the HFA). The NSRN is incremented by the number of
// registers used. The argument has now been allocated."
//
// N.b. As above, this rule is the responsibility of the front-end.
// "C.3: If the argument is an HFA then the NSRN is set to 8 and the size of
// the argument is rounded up to the nearest multiple of 8 bytes."
//
// "C.4: If the argument is an HFA, a Quad-precision Floating-point or Short
// Vector Type then the NSAA is rounded up to the larger of 8 or the Natural
// Alignment of the Argument's type."
//
// It is expected that these will be satisfied by adding dummy arguments to
// the prototype.
// PCS: "C.5: If the argument is a Half- or Single- precision Floating-point
// type then the size of the argument is set to 8 bytes. The effect is as if
// the argument had been copied to the least significant bits of a 64-bit
// register and the remaining bits filled with unspecified values."
CCIfType<[f16, f32], CCPromoteToType<f64>>,
// PCS: "C.6: If the argument is an HFA, a Half-, Single-, Double- or Quad-
// precision Floating-point or Short Vector Type, then the argument is copied
// to memory at the adjusted NSAA. The NSAA is incremented by the size of the
// argument. The argument has now been allocated."
CCIfType<[f64], CCAssignToStack<8, 8>>,
CCIfType<[f128], CCAssignToStack<16, 16>>,
// PCS: "C.7: If the argument is an Integral Type, the size of the argument is
// less than or equal to 8 bytes and the NGRN is less than 8, the argument is
// copied to the least significant bits of x[NGRN]. The NGRN is incremented by
// one. The argument has now been allocated."
// First we implement C.8 and C.9 (128-bit types get even registers). i128 is
// represented as two i64s, the first one being split. If we delayed this
// operation C.8 would never be reached.
CCIfType<[i64],
CCIfSplit<CCAssignToRegWithShadow<[X0, X2, X4, X6], [X0, X1, X3, X5]>>>,
// Note: the promotion also implements C.14.
CCIfType<[i8, i16, i32], CCPromoteToType<i64>>,
// And now the real implementation of C.7
CCIfType<[i64], CCAssignToReg<[X0, X1, X2, X3, X4, X5, X6, X7]>>,
// PCS: "C.8: If the argument has an alignment of 16 then the NGRN is rounded
// up to the next even number."
//
// "C.9: If the argument is an Integral Type, the size of the argument is
// equal to 16 and the NGRN is less than 7, the argument is copied to x[NGRN]
// and x[NGRN+1], x[NGRN] shall contain the lower addressed double-word of the
// memory representation of the argument. The NGRN is incremented by two. The
// argument has now been allocated."
//
// Subtlety here: what if alignment is 16 but it is not an integral type? All
// floating-point types have been allocated already, which leaves composite
// types: this is why a front-end may need to produce i128 for a struct <= 16
// bytes.
// PCS: "C.10 If the argument is a Composite Type and the size in double-words
// of the argument is not more than 8 minus NGRN, then the argument is copied
// into consecutive general-purpose registers, starting at x[NGRN]. The
// argument is passed as though it had been loaded into the registers from a
// double-word aligned address with an appropriate sequence of LDR
// instructions loading consecutive registers from memory (the contents of any
// unused parts of the registers are unspecified by this standard). The NGRN
// is incremented by the number of registers used. The argument has now been
// allocated."
//
// Another one that's the responsibility of the front-end (sigh).
// PCS: "C.11: The NGRN is set to 8."
CCCustom<"CC_AArch64NoMoreRegs">,
// PCS: "C.12: The NSAA is rounded up to the larger of 8 or the Natural
// Alignment of the argument's type."
//
// PCS: "C.13: If the argument is a composite type then the argument is copied
// to memory at the adjusted NSAA. The NSAA is by the size of the
// argument. The argument has now been allocated."
//
// Note that the effect of this corresponds to a memcpy rather than register
// stores so that the struct ends up correctly addressable at the adjusted
// NSAA.
// PCS: "C.14: If the size of the argument is less than 8 bytes then the size
// of the argument is set to 8 bytes. The effect is as if the argument was
// copied to the least significant bits of a 64-bit register and the remaining
// bits filled with unspecified values."
//
// Integer types were widened above. Floating-point and composite types have
// already been allocated completely. Nothing to do.
// PCS: "C.15: The argument is copied to memory at the adjusted NSAA. The NSAA
// is incremented by the size of the argument. The argument has now been
// allocated."
CCIfType<[i64], CCIfSplit<CCAssignToStack<8, 16>>>,
CCIfType<[i64], CCAssignToStack<8, 8>>
]>;
// According to the PCS, X19-X30 are callee-saved, however only the low 64-bits
// of vector registers (8-15) are callee-saved. The order here is is picked up
// by PrologEpilogInserter.cpp to allocate stack slots, starting from top of
// stack upon entry. This gives the customary layout of x30 at [sp-8], x29 at
// [sp-16], ...
def CSR_PCS : CalleeSavedRegs<(add (sequence "X%u", 30, 19),
(sequence "D%u", 15, 8))>;
// TLS descriptor calls are extremely restricted in their changes, to allow
// optimisations in the (hopefully) more common fast path where no real action
// is needed. They actually have to preserve all registers, except for the
// unavoidable X30 and the return register X0.
def TLSDesc : CalleeSavedRegs<(add (sequence "X%u", 29, 1),
(sequence "Q%u", 31, 0))>;