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Remove unneeded FunctionCx from some codegen methods #142324

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Jun 11, 2025
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Remove unneeded FunctionCx from some codegen methods #142324

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190 changes: 94 additions & 96 deletions compiler/rustc_codegen_ssa/src/mir/rvalue.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -278,7 +278,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
{
let from_backend_ty = bx.backend_type(operand.layout);
let to_backend_ty = bx.backend_type(cast);
Some(OperandValue::Immediate(self.transmute_immediate(
Some(OperandValue::Immediate(transmute_immediate(
bx,
imm,
from_scalar,
Expand All @@ -303,8 +303,8 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
let out_a_ibty = bx.scalar_pair_element_backend_type(cast, 0, false);
let out_b_ibty = bx.scalar_pair_element_backend_type(cast, 1, false);
Some(OperandValue::Pair(
self.transmute_immediate(bx, imm_a, in_a, in_a_ibty, out_a, out_a_ibty),
self.transmute_immediate(bx, imm_b, in_b, in_b_ibty, out_b, out_b_ibty),
transmute_immediate(bx, imm_a, in_a, in_a_ibty, out_a, out_a_ibty),
transmute_immediate(bx, imm_b, in_b, in_b_ibty, out_b, out_b_ibty),
))
} else {
None
Expand Down Expand Up @@ -332,7 +332,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
// valid ranges. For example, `char`s are passed as just `i32`, with no
// way for LLVM to know that they're 0x10FFFF at most. Thus we assume
// the range of the input value too, not just the output range.
self.assume_scalar_range(bx, imm, from_scalar, from_backend_ty);
assume_scalar_range(bx, imm, from_scalar, from_backend_ty);

imm = match (from_scalar.primitive(), to_scalar.primitive()) {
(Int(_, is_signed), Int(..)) => bx.intcast(imm, to_backend_ty, is_signed),
Expand Down Expand Up @@ -365,98 +365,6 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
Some(imm)
}

/// Transmutes one of the immediates from an [`OperandValue::Immediate`]
/// or an [`OperandValue::Pair`] to an immediate of the target type.
///
/// `to_backend_ty` must be the *non*-immediate backend type (so it will be
/// `i8`, not `i1`, for `bool`-like types.)
fn transmute_immediate(
&self,
bx: &mut Bx,
mut imm: Bx::Value,
from_scalar: abi::Scalar,
from_backend_ty: Bx::Type,
to_scalar: abi::Scalar,
to_backend_ty: Bx::Type,
) -> Bx::Value {
assert_eq!(from_scalar.size(self.cx), to_scalar.size(self.cx));

// While optimizations will remove no-op transmutes, they might still be
// there in debug or things that aren't no-op in MIR because they change
// the Rust type but not the underlying layout/niche.
if from_scalar == to_scalar && from_backend_ty == to_backend_ty {
return imm;
}

use abi::Primitive::*;
imm = bx.from_immediate(imm);

// If we have a scalar, we must already know its range. Either
//
// 1) It's a parameter with `range` parameter metadata,
// 2) It's something we `load`ed with `!range` metadata, or
// 3) After a transmute we `assume`d the range (see below).
//
// That said, last time we tried removing this, it didn't actually help
// the rustc-perf results, so might as well keep doing it
// <https://github.com/rust-lang/rust/pull/135610#issuecomment-2599275182>
self.assume_scalar_range(bx, imm, from_scalar, from_backend_ty);

imm = match (from_scalar.primitive(), to_scalar.primitive()) {
(Int(..) | Float(_), Int(..) | Float(_)) => bx.bitcast(imm, to_backend_ty),
(Pointer(..), Pointer(..)) => bx.pointercast(imm, to_backend_ty),
(Int(..), Pointer(..)) => bx.ptradd(bx.const_null(bx.type_ptr()), imm),
(Pointer(..), Int(..)) => {
// FIXME: this exposes the provenance, which shouldn't be necessary.
bx.ptrtoint(imm, to_backend_ty)
}
(Float(_), Pointer(..)) => {
let int_imm = bx.bitcast(imm, bx.cx().type_isize());
bx.ptradd(bx.const_null(bx.type_ptr()), int_imm)
}
(Pointer(..), Float(_)) => {
// FIXME: this exposes the provenance, which shouldn't be necessary.
let int_imm = bx.ptrtoint(imm, bx.cx().type_isize());
bx.bitcast(int_imm, to_backend_ty)
}
};

// This `assume` remains important for cases like (a conceptual)
// transmute::<u32, NonZeroU32>(x) == 0
// since it's never passed to something with parameter metadata (especially
// after MIR inlining) so the only way to tell the backend about the
// constraint that the `transmute` introduced is to `assume` it.
self.assume_scalar_range(bx, imm, to_scalar, to_backend_ty);

imm = bx.to_immediate_scalar(imm, to_scalar);
imm
}

fn assume_scalar_range(
&self,
bx: &mut Bx,
imm: Bx::Value,
scalar: abi::Scalar,
backend_ty: Bx::Type,
) {
if matches!(self.cx.sess().opts.optimize, OptLevel::No) || scalar.is_always_valid(self.cx) {
return;
}

match scalar.primitive() {
abi::Primitive::Int(..) => {
let range = scalar.valid_range(self.cx);
bx.assume_integer_range(imm, backend_ty, range);
}
abi::Primitive::Pointer(abi::AddressSpace::DATA)
if !scalar.valid_range(self.cx).contains(0) =>
{
bx.assume_nonnull(imm);
}
abi::Primitive::Pointer(..) | abi::Primitive::Float(..) => {}
}
}

pub(crate) fn codegen_rvalue_unsized(
&mut self,
bx: &mut Bx,
Expand Down Expand Up @@ -1231,3 +1139,93 @@ impl OperandValueKind {
})
}
}

/// Transmutes one of the immediates from an [`OperandValue::Immediate`]
/// or an [`OperandValue::Pair`] to an immediate of the target type.
///
/// `to_backend_ty` must be the *non*-immediate backend type (so it will be
/// `i8`, not `i1`, for `bool`-like types.)
fn transmute_immediate<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
bx: &mut Bx,
mut imm: Bx::Value,
from_scalar: abi::Scalar,
from_backend_ty: Bx::Type,
to_scalar: abi::Scalar,
to_backend_ty: Bx::Type,
) -> Bx::Value {
assert_eq!(from_scalar.size(bx.cx()), to_scalar.size(bx.cx()));

// While optimizations will remove no-op transmutes, they might still be
// there in debug or things that aren't no-op in MIR because they change
// the Rust type but not the underlying layout/niche.
if from_scalar == to_scalar && from_backend_ty == to_backend_ty {
return imm;
}

use abi::Primitive::*;
imm = bx.from_immediate(imm);

// If we have a scalar, we must already know its range. Either
//
// 1) It's a parameter with `range` parameter metadata,
// 2) It's something we `load`ed with `!range` metadata, or
// 3) After a transmute we `assume`d the range (see below).
//
// That said, last time we tried removing this, it didn't actually help
// the rustc-perf results, so might as well keep doing it
// <https://github.com/rust-lang/rust/pull/135610#issuecomment-2599275182>
assume_scalar_range(bx, imm, from_scalar, from_backend_ty);

imm = match (from_scalar.primitive(), to_scalar.primitive()) {
(Int(..) | Float(_), Int(..) | Float(_)) => bx.bitcast(imm, to_backend_ty),
(Pointer(..), Pointer(..)) => bx.pointercast(imm, to_backend_ty),
(Int(..), Pointer(..)) => bx.ptradd(bx.const_null(bx.type_ptr()), imm),
(Pointer(..), Int(..)) => {
// FIXME: this exposes the provenance, which shouldn't be necessary.
bx.ptrtoint(imm, to_backend_ty)
}
(Float(_), Pointer(..)) => {
let int_imm = bx.bitcast(imm, bx.cx().type_isize());
bx.ptradd(bx.const_null(bx.type_ptr()), int_imm)
}
(Pointer(..), Float(_)) => {
// FIXME: this exposes the provenance, which shouldn't be necessary.
let int_imm = bx.ptrtoint(imm, bx.cx().type_isize());
bx.bitcast(int_imm, to_backend_ty)
}
};

// This `assume` remains important for cases like (a conceptual)
// transmute::<u32, NonZeroU32>(x) == 0
// since it's never passed to something with parameter metadata (especially
// after MIR inlining) so the only way to tell the backend about the
// constraint that the `transmute` introduced is to `assume` it.
assume_scalar_range(bx, imm, to_scalar, to_backend_ty);

imm = bx.to_immediate_scalar(imm, to_scalar);
imm
}

fn assume_scalar_range<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
bx: &mut Bx,
imm: Bx::Value,
scalar: abi::Scalar,
backend_ty: Bx::Type,
) {
if matches!(bx.cx().sess().opts.optimize, OptLevel::No) || scalar.is_always_valid(bx.cx()) {
return;
}

match scalar.primitive() {
abi::Primitive::Int(..) => {
let range = scalar.valid_range(bx.cx());
bx.assume_integer_range(imm, backend_ty, range);
}
abi::Primitive::Pointer(abi::AddressSpace::DATA)
if !scalar.valid_range(bx.cx()).contains(0) =>
{
bx.assume_nonnull(imm);
}
abi::Primitive::Pointer(..) | abi::Primitive::Float(..) => {}
}
}
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