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Don't compute FnAbi for LLVM intrinsics in backends #150768

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Merged
rust-bors merged 3 commits into from
Feb 12, 2026
Merged

Don't compute FnAbi for LLVM intrinsics in backends #150768

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acc8c0b
Reduce usage of FnAbi in codegen_llvm_intrinsic_call
bjorn3 Dec 28, 2025
f1ab003
Don't compute FnAbi for LLVM intrinsics in backends
bjorn3 Jan 8, 2026
fe9715b
Remove support for ScalarPair unadjusted arguments
bjorn3 Jan 8, 2026
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88 changes: 84 additions & 4 deletions compiler/rustc_codegen_gcc/src/intrinsic/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -4,10 +4,10 @@ mod simd;
#[cfg(feature = "master")]
use std::iter;

#[cfg(feature = "master")]
use gccjit::Type;
use gccjit::{ComparisonOp, Function, FunctionType, RValue, ToRValue, UnaryOp};
#[cfg(feature = "master")]
use gccjit::{FnAttribute, Type};
#[cfg(feature = "master")]
use rustc_abi::ExternAbi;
use rustc_abi::{BackendRepr, HasDataLayout, WrappingRange};
use rustc_codegen_ssa::MemFlags;
Expand All @@ -22,13 +22,18 @@ use rustc_codegen_ssa::traits::{
ArgAbiBuilderMethods, BaseTypeCodegenMethods, BuilderMethods, ConstCodegenMethods,
IntrinsicCallBuilderMethods, LayoutTypeCodegenMethods,
};
use rustc_data_structures::fx::FxHashSet;
use rustc_middle::bug;
use rustc_middle::ty::layout::{FnAbiOf, LayoutOf};
use rustc_middle::ty::{self, Instance, Ty};
#[cfg(feature = "master")]
use rustc_session::config;
use rustc_span::{Span, Symbol, sym};
#[cfg(feature = "master")]
use rustc_target::callconv::ArgAttributes;
use rustc_target::callconv::{ArgAbi, PassMode};

use crate::abi::{FnAbiGccExt, GccType};
use crate::abi::{FnAbiGcc, FnAbiGccExt, GccType};
use crate::builder::Builder;
use crate::common::{SignType, TypeReflection};
use crate::context::CodegenCx;
Expand Down Expand Up @@ -621,7 +626,82 @@ impl<'a, 'gcc, 'tcx> IntrinsicCallBuilderMethods<'tcx> for Builder<'a, 'gcc, 'tc
} else {
self.linkage.set(FunctionType::Extern);
let fn_abi = self.fn_abi_of_instance(instance, ty::List::empty());
let fn_ty = fn_abi.gcc_type(self);
assert!(!fn_abi.ret.is_indirect());
assert!(!fn_abi.c_variadic);

let return_type = match fn_abi.ret.mode {
PassMode::Ignore => self.type_void(),
PassMode::Direct(_) | PassMode::Pair(..) => {
fn_abi.ret.layout.immediate_gcc_type(self)
}
PassMode::Cast { .. } | PassMode::Indirect { .. } => {
unreachable!()
}
};

#[cfg(feature = "master")]
let mut non_null_args = Vec::new();

#[cfg(feature = "master")]
let mut apply_attrs =
|mut ty: Type<'gcc>, attrs: &ArgAttributes, arg_index: usize| {
if self.sess().opts.optimize == config::OptLevel::No {
return ty;
}
if attrs.regular.contains(rustc_target::callconv::ArgAttribute::NoAlias) {
ty = ty.make_restrict()
}
if attrs.regular.contains(rustc_target::callconv::ArgAttribute::NonNull) {
non_null_args.push(arg_index as i32 + 1);
}
ty
};
#[cfg(not(feature = "master"))]
let apply_attrs = |ty: Type<'gcc>, _attrs: &ArgAttributes, _arg_index: usize| ty;

let mut argument_tys = Vec::with_capacity(fn_abi.args.len());
for arg in fn_abi.args.iter() {
match arg.mode {
PassMode::Ignore => {}
PassMode::Pair(a, b) => {
let arg_pos = argument_tys.len();
argument_tys.push(apply_attrs(
arg.layout.scalar_pair_element_gcc_type(self, 0),
&a,
arg_pos,
));
argument_tys.push(apply_attrs(
arg.layout.scalar_pair_element_gcc_type(self, 1),
&b,
arg_pos + 1,
));
}
PassMode::Direct(attrs) => argument_tys.push(apply_attrs(
arg.layout.immediate_gcc_type(self),
&attrs,
argument_tys.len(),
)),
PassMode::Indirect { .. } | PassMode::Cast { .. } => {
unreachable!()
}
}
}

#[cfg(feature = "master")]
let fn_attrs = if non_null_args.is_empty() {
Vec::new()
} else {
vec![FnAttribute::NonNull(non_null_args)]
};

let fn_ty = FnAbiGcc {
return_type,
arguments_type: argument_tys,
is_c_variadic: false,
on_stack_param_indices: FxHashSet::default(),
#[cfg(feature = "master")]
fn_attributes: fn_attrs,
};

let func = match sym {
"llvm.fma.f16" => {
Expand Down
30 changes: 27 additions & 3 deletions compiler/rustc_codegen_llvm/src/intrinsic.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -649,7 +649,32 @@ impl<'ll, 'tcx> IntrinsicCallBuilderMethods<'tcx> for Builder<'_, 'll, 'tcx> {
// FIXME remove usage of fn_abi
let fn_abi = self.fn_abi_of_instance(instance, ty::List::empty());
assert!(!fn_abi.ret.is_indirect());
let fn_ty = fn_abi.llvm_type(self);
assert!(!fn_abi.c_variadic);

let llreturn_ty = match &fn_abi.ret.mode {
PassMode::Ignore => self.type_void(),
PassMode::Direct(_) | PassMode::Pair(..) => fn_abi.ret.layout.immediate_llvm_type(self),
PassMode::Cast { .. } | PassMode::Indirect { .. } => {
unreachable!()
}
};

let mut llargument_tys = Vec::with_capacity(fn_abi.args.len());
for arg in &fn_abi.args {
match &arg.mode {
PassMode::Ignore => {}
PassMode::Direct(_) => llargument_tys.push(arg.layout.immediate_llvm_type(self)),
PassMode::Pair(..) => {
llargument_tys.push(arg.layout.scalar_pair_element_llvm_type(self, 0, true));
llargument_tys.push(arg.layout.scalar_pair_element_llvm_type(self, 1, true));
}
PassMode::Indirect { .. } | PassMode::Cast { .. } => {
unreachable!()
}
};
}

let fn_ty = self.type_func(&llargument_tys, llreturn_ty);

let fn_ptr = if let Some(&llfn) = self.intrinsic_instances.borrow().get(&instance) {
llfn
Expand All @@ -665,12 +690,11 @@ impl<'ll, 'tcx> IntrinsicCallBuilderMethods<'tcx> for Builder<'_, 'll, 'tcx> {
let llfn = declare_raw_fn(
self,
sym,
fn_abi.llvm_cconv(self),
llvm::CCallConv,
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@Mark-Simulacrum Mark-Simulacrum Feb 8, 2026

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Is this effectively just a lie? Or how does LLVM model the ABI for intrinsics? Is there a hidden assumption here that intrinsics only ever take ~integers/pointers that don't have any special handling in terms of ABI lowering of the arguments?

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@bjorn3 bjorn3 Feb 8, 2026

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This matches what was effectively done previously. I don't know if LLVM actually cares about the calling convention for intrinsics. It recognizes intrinsics based on a builtin list of symbol names. (if you declare an llvm.* function that doesn't match a known intrinsic, it will treat it like a regular function and emit an import of said function in the emitted object file)

llvm::UnnamedAddr::Global,
llvm::Visibility::Default,
fn_ty,
);
fn_abi.apply_attrs_llfn(self, llfn, Some(instance));

llfn
};
Expand Down