// Rust asm! and GCC Extended Asm semantics differ substantially.
//
-// 1. Rust asm operands go along as one list of operands. Operands themselves indicate
-// if they're "in" or "out". "In" and "out" operands can interleave. One operand can be
+// 1. Rust asm operands go along as one list of operands. Operands themselves indicate
+// if they're "in" or "out". "In" and "out" operands can interleave. One operand can be
// both "in" and "out" (`inout(reg)`).
//
-// GCC asm has two different lists for "in" and "out" operands. In terms of gccjit,
-// this means that all "out" operands must go before "in" operands. "In" and "out" operands
+// GCC asm has two different lists for "in" and "out" operands. In terms of gccjit,
+// this means that all "out" operands must go before "in" operands. "In" and "out" operands
// cannot interleave.
//
-// 2. Operand lists in both Rust and GCC are indexed. Index starts from 0. Indexes are important
+// 2. Operand lists in both Rust and GCC are indexed. Index starts from 0. Indexes are important
// because the asm template refers to operands by index.
//
// Mapping from Rust to GCC index would be 1-1 if it wasn't for...
//
-// 3. Clobbers. GCC has a separate list of clobbers, and clobbers don't have indexes.
-// Contrary, Rust expresses clobbers through "out" operands that aren't tied to
+// 3. Clobbers. GCC has a separate list of clobbers, and clobbers don't have indexes.
+// Contrary, Rust expresses clobbers through "out" operands that aren't tied to
// a variable (`_`), and such "clobbers" do have index.
//
-// 4. Furthermore, GCC Extended Asm does not support explicit register constraints
-// (like `out("eax")`) directly, offering so-called "local register variables"
-// as a workaround. These variables need to be declared and initialized *before*
-// the Extended Asm block but *after* normal local variables
+// 4. Furthermore, GCC Extended Asm does not support explicit register constraints
+// (like `out("eax")`) directly, offering so-called "local register variables"
+// as a workaround. These variables need to be declared and initialized *before*
+// the Extended Asm block but *after* normal local variables
// (see comment in `codegen_inline_asm` for explanation).
//
-// With that in mind, let's see how we translate Rust syntax to GCC
+// With that in mind, let's see how we translate Rust syntax to GCC
// (from now on, `CC` stands for "constraint code"):
//
// * `out(reg_class) var` -> translated to output operand: `"=CC"(var)`
//
// * `out("explicit register") _` -> not translated to any operands, register is simply added to clobbers list
//
-// * `inout(reg_class) in_var => out_var` -> translated to two operands:
+// * `inout(reg_class) in_var => out_var` -> translated to two operands:
// output: `"=CC"(in_var)`
-// input: `"num"(out_var)` where num is the GCC index
+// input: `"num"(out_var)` where num is the GCC index
// of the corresponding output operand
//
-// * `inout(reg_class) in_var => _` -> same as `inout(reg_class) in_var => tmp`,
+// * `inout(reg_class) in_var => _` -> same as `inout(reg_class) in_var => tmp`,
// where "tmp" is a temporary unused variable
//
-// * `out/in/inout("explicit register") var` -> translated to one or two operands as described above
-// with `"r"(var)` constraint,
+// * `out/in/inout("explicit register") var` -> translated to one or two operands as described above
+// with `"r"(var)` constraint,
// and one register variable assigned to the desired register.
-//
const ATT_SYNTAX_INS: &str = ".att_syntax noprefix\n\t";
const INTEL_SYNTAX_INS: &str = "\n\t.intel_syntax noprefix";
let att_dialect = is_x86 && options.contains(InlineAsmOptions::ATT_SYNTAX);
let intel_dialect = is_x86 && !options.contains(InlineAsmOptions::ATT_SYNTAX);
- // GCC index of an output operand equals its position in the array
+ // GCC index of an output operand equals its position in the array
let mut outputs = vec![];
// GCC index of an input operand equals its position in the array
let mut constants_len = 0;
// There are rules we must adhere to if we want GCC to do the right thing:
- //
+ //
// * Every local variable that the asm block uses as an output must be declared *before*
- // the asm block.
+ // the asm block.
// * There must be no instructions whatsoever between the register variables and the asm.
//
// Therefore, the backend must generate the instructions strictly in this order:
// We also must make sure that no input operands are emitted before output operands.
//
// This is why we work in passes, first emitting local vars, then local register vars.
- // Also, we don't emit any asm operands immediately; we save them to
+ // Also, we don't emit any asm operands immediately; we save them to
// the one of the buffers to be emitted later.
// 1. Normal variables (and saving operands to buffers).
(Constraint(constraint), Some(place)) => (constraint, place.layout.gcc_type(self.cx, false)),
// When `reg` is a class and not an explicit register but the out place is not specified,
// we need to create an unused output variable to assign the output to. This var
- // needs to be of a type that's "compatible" with the register class, but specific type
+ // needs to be of a type that's "compatible" with the register class, but specific type
// doesn't matter.
(Constraint(constraint), None) => (constraint, dummy_output_type(self.cx, reg.reg_class())),
(Register(_), Some(_)) => {
let tmp_var = self.current_func().new_local(None, ty, "output_register");
outputs.push(AsmOutOperand {
- constraint,
+ constraint,
rust_idx,
late,
readwrite: false,
InlineAsmOperandRef::In { reg, value } => {
if let ConstraintOrRegister::Constraint(constraint) = reg_to_gcc(reg) {
- inputs.push(AsmInOperand {
- constraint: Cow::Borrowed(constraint),
- rust_idx,
+ inputs.push(AsmInOperand {
+ constraint: Cow::Borrowed(constraint),
+ rust_idx,
val: value.immediate()
});
- }
+ }
else {
// left for the next pass
continue
InlineAsmOperandRef::InOut { reg, late, in_value, out_place } => {
let constraint = if let ConstraintOrRegister::Constraint(constraint) = reg_to_gcc(reg) {
constraint
- }
+ }
else {
// left for the next pass
continue
// Rustc frontend guarantees that input and output types are "compatible",
// so we can just use input var's type for the output variable.
//
- // This decision is also backed by the fact that LLVM needs in and out
- // values to be of *exactly the same type*, not just "compatible".
+ // This decision is also backed by the fact that LLVM needs in and out
+ // values to be of *exactly the same type*, not just "compatible".
// I'm not sure if GCC is so picky too, but better safe than sorry.
let ty = in_value.layout.gcc_type(self.cx, false);
let tmp_var = self.current_func().new_local(None, ty, "output_register");
// If the out_place is None (i.e `inout(reg) _` syntax was used), we translate
- // it to one "readwrite (+) output variable", otherwise we translate it to two
+ // it to one "readwrite (+) output variable", otherwise we translate it to two
// "out and tied in" vars as described above.
let readwrite = out_place.is_none();
outputs.push(AsmOutOperand {
- constraint,
+ constraint,
rust_idx,
late,
readwrite,
- tmp_var,
+ tmp_var,
out_place,
});
let constraint = Cow::Owned(out_gcc_idx.to_string());
inputs.push(AsmInOperand {
- constraint,
- rust_idx,
+ constraint,
+ rust_idx,
val: in_value.immediate()
});
}
if let ConstraintOrRegister::Register(reg_name) = reg_to_gcc(reg) {
let out_place = if let Some(place) = place {
place
- }
+ }
else {
// processed in the previous pass
continue
tmp_var.set_register_name(reg_name);
outputs.push(AsmOutOperand {
- constraint: "r".into(),
+ constraint: "r".into(),
rust_idx,
late,
readwrite: false,
reg_var.set_register_name(reg_name);
self.llbb().add_assignment(None, reg_var, value.immediate());
- inputs.push(AsmInOperand {
- constraint: "r".into(),
- rust_idx,
+ inputs.push(AsmInOperand {
+ constraint: "r".into(),
+ rust_idx,
val: reg_var.to_rvalue()
});
}
// `inout("explicit register") in_var => out_var`
InlineAsmOperandRef::InOut { reg, late, in_value, out_place } => {
if let ConstraintOrRegister::Register(reg_name) = reg_to_gcc(reg) {
- let out_place = if let Some(place) = out_place {
- place
- }
- else {
- // processed in the previous pass
- continue
- };
-
// See explanation in the first pass.
let ty = in_value.layout.gcc_type(self.cx, false);
let tmp_var = self.current_func().new_local(None, ty, "output_register");
tmp_var.set_register_name(reg_name);
outputs.push(AsmOutOperand {
- constraint: "r".into(),
+ constraint: "r".into(),
rust_idx,
late,
readwrite: false,
tmp_var,
- out_place: Some(out_place)
+ out_place,
});
let constraint = Cow::Owned((outputs.len() - 1).to_string());
- inputs.push(AsmInOperand {
- constraint,
+ inputs.push(AsmInOperand {
+ constraint,
rust_idx,
val: in_value.immediate()
});
// processed in the previous pass
}
- InlineAsmOperandRef::Const { .. }
- | InlineAsmOperandRef::SymFn { .. }
+ InlineAsmOperandRef::Const { .. }
+ | InlineAsmOperandRef::SymFn { .. }
| InlineAsmOperandRef::SymStatic { .. } => {
// processed in the previous pass
}
if !intel_dialect {
template_str.push_str(INTEL_SYNTAX_INS);
}
-
+
// 4. Generate Extended Asm block
let block = self.llbb();
}
if !options.contains(InlineAsmOptions::PRESERVES_FLAGS) {
- // TODO(@Commeownist): I'm not 100% sure this one clobber is sufficient
+ // TODO(@Commeownist): I'm not 100% sure this one clobber is sufficient
// on all architectures. For instance, what about FP stack?
extended_asm.add_clobber("cc");
}
self.call(self.type_void(), builtin_unreachable, &[], None);
}
- // Write results to outputs.
+ // Write results to outputs.
//
// We need to do this because:
- // 1. Turning `PlaceRef` into `RValue` is error-prone and has nasty edge cases
+ // 1. Turning `PlaceRef` into `RValue` is error-prone and has nasty edge cases
// (especially with current `rustc_backend_ssa` API).
// 2. Not every output operand has an `out_place`, and it's required by `add_output_operand`.
//
// generates `out_place = tmp_var;` assignments if out_place exists.
for op in &outputs {
if let Some(place) = op.out_place {
- OperandValue::Immediate(op.tmp_var.to_rvalue()).store(self, place);
+ OperandValue::Immediate(op.tmp_var.to_rvalue()).store(self, place);
}
}
projects / rust.git / blobdiff