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Separate immediate and in-memory ScalarPair representation #118991

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4 changes: 2 additions & 2 deletions compiler/rustc_codegen_llvm/src/abi.rs
Original file line number Diff line number Diff line change
Expand Up @@ -6,7 +6,7 @@ use crate::type_::Type;
use crate::type_of::LayoutLlvmExt;
use crate::value::Value;

use rustc_codegen_ssa::mir::operand::OperandValue;
use rustc_codegen_ssa::mir::operand::{OperandRef, OperandValue};
use rustc_codegen_ssa::mir::place::PlaceRef;
use rustc_codegen_ssa::traits::*;
use rustc_codegen_ssa::MemFlags;
Expand Down Expand Up @@ -253,7 +253,7 @@ impl<'ll, 'tcx> ArgAbiExt<'ll, 'tcx> for ArgAbi<'tcx, Ty<'tcx>> {
bx.lifetime_end(llscratch, scratch_size);
}
} else {
OperandValue::Immediate(val).store(bx, dst);
OperandRef::from_immediate_or_packed_pair(bx, val, self.layout).val.store(bx, dst);
}
}

Expand Down
11 changes: 9 additions & 2 deletions compiler/rustc_codegen_llvm/src/builder.rs
Original file line number Diff line number Diff line change
Expand Up @@ -558,10 +558,17 @@ impl<'a, 'll, 'tcx> BuilderMethods<'a, 'tcx> for Builder<'a, 'll, 'tcx> {
OperandValue::Immediate(self.to_immediate(llval, place.layout))
} else if let abi::Abi::ScalarPair(a, b) = place.layout.abi {
let b_offset = a.size(self).align_to(b.align(self).abi);
let pair_ty = place.layout.llvm_type(self);

let mut load = |i, scalar: abi::Scalar, layout, align, offset| {
let llptr = self.struct_gep(pair_ty, place.llval, i as u64);
let llptr = if i == 0 {
place.llval
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Hm, this if seems like a code smell to me. Since there are just two calls to this closure (as far as I can tell) and this if is the sole use of the i argument, perhaps consider constructing the llptr in the caller and passing it into the closure instead?

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The i argument is also used to determine llty.

I've tried moving this into the caller, but this ends up being rather ugly, especially as self is captured by the closure, so we can't use it outside without further changes.

} else {
self.inbounds_gep(
self.type_i8(),
place.llval,
&[self.const_usize(b_offset.bytes())],
)
};
let llty = place.layout.scalar_pair_element_llvm_type(self, i, false);
let load = self.load(llty, llptr, align);
scalar_load_metadata(self, load, scalar, layout, offset);
Expand Down
5 changes: 4 additions & 1 deletion compiler/rustc_codegen_llvm/src/intrinsic.rs
Original file line number Diff line number Diff line change
Expand Up @@ -179,7 +179,10 @@ impl<'ll, 'tcx> IntrinsicCallMethods<'tcx> for Builder<'_, 'll, 'tcx> {
unsafe {
llvm::LLVMSetAlignment(load, align);
}
self.to_immediate(load, self.layout_of(tp_ty))
if !result.layout.is_zst() {
self.store(load, result.llval, result.align);
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Why was this change necessary? Is it because there might now be trailing padding where previously there wasn’t any?

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The volatile_load implementation blindly loads the value using the in-memory type, so it can produce loads of array and (arbitrary) struct types. These are not really valid immediates as far as rustc is concerned (and non-canonical as far as LLVM is concerned).

The way this ends up getting handled is that if the value has Scalar ABI we convert it to an immediate, while everything else is left alone. After this change, this no longer works for ScalarPair ABI, which would need an adjustment.

What this change does it to never treat the value as an immediate in the first place, and just directly store it back in in-memory representation.

The implementation of volatile_load is really questionable in general (we really shouldn't be generating array/struct loads), but it's not really clear how it should be implemented given that we made the major design mistake of allowing volatile loads of arbitrary types, which is not a well-defined operation. We just leave it up to LLVM to interpret this in some way...

}
return;
}
sym::volatile_store => {
let dst = args[0].deref(self.cx());
Expand Down
33 changes: 19 additions & 14 deletions compiler/rustc_codegen_llvm/src/type_of.rs
Original file line number Diff line number Diff line change
Expand Up @@ -26,16 +26,7 @@ fn uncached_llvm_type<'a, 'tcx>(
let element = layout.scalar_llvm_type_at(cx, element);
return cx.type_vector(element, count);
}
Abi::ScalarPair(..) => {
return cx.type_struct(
&[
layout.scalar_pair_element_llvm_type(cx, 0, false),
layout.scalar_pair_element_llvm_type(cx, 1, false),
],
false,
);
}
Abi::Uninhabited | Abi::Aggregate { .. } => {}
Abi::Uninhabited | Abi::Aggregate { .. } | Abi::ScalarPair(..) => {}
}

let name = match layout.ty.kind() {
Expand Down Expand Up @@ -275,11 +266,25 @@ impl<'tcx> LayoutLlvmExt<'tcx> for TyAndLayout<'tcx> {
}

fn immediate_llvm_type<'a>(&self, cx: &CodegenCx<'a, 'tcx>) -> &'a Type {
if let Abi::Scalar(scalar) = self.abi {
if scalar.is_bool() {
return cx.type_i1();
match self.abi {
Abi::Scalar(scalar) => {
if scalar.is_bool() {
return cx.type_i1();
}
}
}
Abi::ScalarPair(..) => {
// An immediate pair always contains just the two elements, without any padding
// filler, as it should never be stored to memory.
return cx.type_struct(
&[
self.scalar_pair_element_llvm_type(cx, 0, true),
self.scalar_pair_element_llvm_type(cx, 1, true),
],
false,
);
}
_ => {}
};
self.llvm_type(cx)
}

Expand Down
19 changes: 7 additions & 12 deletions compiler/rustc_codegen_ssa/src/mir/operand.rs
Original file line number Diff line number Diff line change
Expand Up @@ -231,14 +231,12 @@ impl<'a, 'tcx, V: CodegenObject> OperandRef<'tcx, V> {
bx: &mut Bx,
) -> V {
if let OperandValue::Pair(a, b) = self.val {
let llty = bx.cx().backend_type(self.layout);
let llty = bx.cx().immediate_backend_type(self.layout);
debug!("Operand::immediate_or_packed_pair: packing {:?} into {:?}", self, llty);
// Reconstruct the immediate aggregate.
let mut llpair = bx.cx().const_poison(llty);
let imm_a = bx.from_immediate(a);
let imm_b = bx.from_immediate(b);
llpair = bx.insert_value(llpair, imm_a, 0);
llpair = bx.insert_value(llpair, imm_b, 1);
llpair = bx.insert_value(llpair, a, 0);
llpair = bx.insert_value(llpair, b, 1);
llpair
} else {
self.immediate()
Expand All @@ -251,14 +249,12 @@ impl<'a, 'tcx, V: CodegenObject> OperandRef<'tcx, V> {
llval: V,
layout: TyAndLayout<'tcx>,
) -> Self {
let val = if let Abi::ScalarPair(a, b) = layout.abi {
let val = if let Abi::ScalarPair(..) = layout.abi {
debug!("Operand::from_immediate_or_packed_pair: unpacking {:?} @ {:?}", llval, layout);

// Deconstruct the immediate aggregate.
let a_llval = bx.extract_value(llval, 0);
let a_llval = bx.to_immediate_scalar(a_llval, a);
let b_llval = bx.extract_value(llval, 1);
let b_llval = bx.to_immediate_scalar(b_llval, b);
OperandValue::Pair(a_llval, b_llval)
} else {
OperandValue::Immediate(llval)
Expand Down Expand Up @@ -435,15 +431,14 @@ impl<'a, 'tcx, V: CodegenObject> OperandValue<V> {
let Abi::ScalarPair(a_scalar, b_scalar) = dest.layout.abi else {
bug!("store_with_flags: invalid ScalarPair layout: {:#?}", dest.layout);
};
let ty = bx.backend_type(dest.layout);
let b_offset = a_scalar.size(bx).align_to(b_scalar.align(bx).abi);

let llptr = bx.struct_gep(ty, dest.llval, 0);
let val = bx.from_immediate(a);
let align = dest.align;
bx.store_with_flags(val, llptr, align, flags);
bx.store_with_flags(val, dest.llval, align, flags);

let llptr = bx.struct_gep(ty, dest.llval, 1);
let llptr =
bx.inbounds_gep(bx.type_i8(), dest.llval, &[bx.const_usize(b_offset.bytes())]);
let val = bx.from_immediate(b);
let align = dest.align.restrict_for_offset(b_offset);
bx.store_with_flags(val, llptr, align, flags);
Expand Down
15 changes: 6 additions & 9 deletions compiler/rustc_codegen_ssa/src/mir/place.rs
Original file line number Diff line number Diff line change
Expand Up @@ -108,20 +108,17 @@ impl<'a, 'tcx, V: CodegenObject> PlaceRef<'tcx, V> {
// Also handles the first field of Scalar, ScalarPair, and Vector layouts.
self.llval
}
Abi::ScalarPair(a, b)
if offset == a.size(bx.cx()).align_to(b.align(bx.cx()).abi) =>
{
// Offset matches second field.
let ty = bx.backend_type(self.layout);
bx.struct_gep(ty, self.llval, 1)
Abi::ScalarPair(..) => {
// FIXME(nikic): Generate this for all ABIs.
bx.inbounds_gep(bx.type_i8(), self.llval, &[bx.const_usize(offset.bytes())])
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}
Abi::Scalar(_) | Abi::ScalarPair(..) | Abi::Vector { .. } if field.is_zst() => {
Abi::Scalar(_) | Abi::Vector { .. } if field.is_zst() => {
// ZST fields (even some that require alignment) are not included in Scalar,
// ScalarPair, and Vector layouts, so manually offset the pointer.
bx.gep(bx.cx().type_i8(), self.llval, &[bx.const_usize(offset.bytes())])
}
Abi::Scalar(_) | Abi::ScalarPair(..) => {
// All fields of Scalar and ScalarPair layouts must have been handled by this point.
Abi::Scalar(_) => {
// All fields of Scalar layouts must have been handled by this point.
// Vector layouts have additional fields for each element of the vector, so don't panic in that case.
bug!(
"offset of non-ZST field `{:?}` does not match layout `{:#?}`",
Expand Down
24 changes: 12 additions & 12 deletions tests/codegen/align-byval.rs
Original file line number Diff line number Diff line change
Expand Up @@ -106,21 +106,21 @@ pub struct ForceAlign16 {
pub unsafe fn call_na1(x: NaturalAlign1) {
// CHECK: start:

// m68k: [[ALLOCA:%[a-z0-9+]]] = alloca { i8, i8 }, align 1
// m68k: call void @natural_align_1({{.*}}byval({ i8, i8 }) align 1{{.*}} [[ALLOCA]])
// m68k: [[ALLOCA:%[a-z0-9+]]] = alloca %NaturalAlign1, align 1
// m68k: call void @natural_align_1({{.*}}byval(%NaturalAlign1) align 1{{.*}} [[ALLOCA]])

// wasm: [[ALLOCA:%[a-z0-9+]]] = alloca { i8, i8 }, align 1
// wasm: call void @natural_align_1({{.*}}byval({ i8, i8 }) align 1{{.*}} [[ALLOCA]])
// wasm: [[ALLOCA:%[a-z0-9+]]] = alloca %NaturalAlign1, align 1
// wasm: call void @natural_align_1({{.*}}byval(%NaturalAlign1) align 1{{.*}} [[ALLOCA]])

// x86_64-linux: call void @natural_align_1(i16

// x86_64-windows: call void @natural_align_1(i16

// i686-linux: [[ALLOCA:%[a-z0-9+]]] = alloca { i8, i8 }, align 4
// i686-linux: call void @natural_align_1({{.*}}byval({ i8, i8 }) align 4{{.*}} [[ALLOCA]])
// i686-linux: [[ALLOCA:%[a-z0-9+]]] = alloca %NaturalAlign1, align 4
// i686-linux: call void @natural_align_1({{.*}}byval(%NaturalAlign1) align 4{{.*}} [[ALLOCA]])

// i686-windows: [[ALLOCA:%[a-z0-9+]]] = alloca { i8, i8 }, align 4
// i686-windows: call void @natural_align_1({{.*}}byval({ i8, i8 }) align 4{{.*}} [[ALLOCA]])
// i686-windows: [[ALLOCA:%[a-z0-9+]]] = alloca %NaturalAlign1, align 4
// i686-windows: call void @natural_align_1({{.*}}byval(%NaturalAlign1) align 4{{.*}} [[ALLOCA]])
natural_align_1(x);
}

Expand Down Expand Up @@ -199,17 +199,17 @@ pub unsafe fn call_fa16(x: ForceAlign16) {
}

extern "C" {
// m68k: declare void @natural_align_1({{.*}}byval({ i8, i8 }) align 1{{.*}})
// m68k: declare void @natural_align_1({{.*}}byval(%NaturalAlign1) align 1{{.*}})

// wasm: declare void @natural_align_1({{.*}}byval({ i8, i8 }) align 1{{.*}})
// wasm: declare void @natural_align_1({{.*}}byval(%NaturalAlign1) align 1{{.*}})

// x86_64-linux: declare void @natural_align_1(i16)

// x86_64-windows: declare void @natural_align_1(i16)

// i686-linux: declare void @natural_align_1({{.*}}byval({ i8, i8 }) align 4{{.*}})
// i686-linux: declare void @natural_align_1({{.*}}byval(%NaturalAlign1) align 4{{.*}})

// i686-windows: declare void @natural_align_1({{.*}}byval({ i8, i8 }) align 4{{.*}})
// i686-windows: declare void @natural_align_1({{.*}}byval(%NaturalAlign1) align 4{{.*}})
fn natural_align_1(x: NaturalAlign1);

// m68k: declare void @natural_align_2({{.*}}byval(%NaturalAlign2) align 2{{.*}})
Expand Down
2 changes: 1 addition & 1 deletion tests/codegen/align-struct.rs
Original file line number Diff line number Diff line change
Expand Up @@ -57,7 +57,7 @@ pub fn nested64(a: Align64, b: i32, c: i32, d: i8) -> Nested64 {
// CHECK-LABEL: @enum4
#[no_mangle]
pub fn enum4(a: i32) -> Enum4 {
// CHECK: %e4 = alloca { i32, i32 }, align 4
// CHECK: %e4 = alloca %Enum4, align 4
let e4 = Enum4::A(a);
e4
}
Expand Down
4 changes: 2 additions & 2 deletions tests/codegen/function-arguments-noopt.rs
Original file line number Diff line number Diff line change
Expand Up @@ -55,7 +55,7 @@ pub fn struct_call(x: S, f: fn(S) -> S) -> S {
f(x)
}

// CHECK: { i8, i8 } @enum_(i1 zeroext %x.0, i8 %x.1)
// CHECK: { i1, i8 } @enum_(i1 zeroext %x.0, i8 %x.1)
#[no_mangle]
pub fn enum_(x: Option<u8>) -> Option<u8> {
x
Expand All @@ -64,6 +64,6 @@ pub fn enum_(x: Option<u8>) -> Option<u8> {
// CHECK-LABEL: @enum_call
#[no_mangle]
pub fn enum_call(x: Option<u8>, f: fn(Option<u8>) -> Option<u8>) -> Option<u8> {
// CHECK: call { i8, i8 } %f(i1 zeroext %x.0, i8 %x.1)
// CHECK: call { i1, i8 } %f(i1 zeroext %x.0, i8 %x.1)
f(x)
}
2 changes: 1 addition & 1 deletion tests/codegen/function-arguments.rs
Original file line number Diff line number Diff line change
Expand Up @@ -275,7 +275,7 @@ pub fn enum_id_1(x: Option<Result<u16, u16>>) -> Option<Result<u16, u16>> {
x
}

// CHECK: { i8, i8 } @enum_id_2(i1 noundef zeroext %x.0, i8 %x.1)
// CHECK: { i1, i8 } @enum_id_2(i1 noundef zeroext %x.0, i8 %x.1)
#[no_mangle]
pub fn enum_id_2(x: Option<u8>) -> Option<u8> {
x
Expand Down
10 changes: 5 additions & 5 deletions tests/codegen/intrinsics/transmute.rs
Original file line number Diff line number Diff line change
Expand Up @@ -190,7 +190,7 @@ pub unsafe fn check_byte_from_bool(x: bool) -> u8 {
// CHECK-LABEL: @check_to_pair(
#[no_mangle]
pub unsafe fn check_to_pair(x: u64) -> Option<i32> {
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// CHECK: %_0 = alloca { i32, i32 }, align 4
// CHECK: %_0 = alloca %"core::option::Option<i32>", align 4
// CHECK: store i64 %x, ptr %_0, align 4
transmute(x)
}
Expand All @@ -203,10 +203,10 @@ pub unsafe fn check_from_pair(x: Option<i32>) -> u64 {
const { assert!(std::mem::align_of::<Option<i32>>() == 4) };

// CHECK: %_0 = alloca i64, align 8
// CHECK: store i32 %x.0, ptr %0, align 8
// CHECK: store i32 %x.1, ptr %1, align 4
// CHECK: %2 = load i64, ptr %_0, align 8
// CHECK: ret i64 %2
// CHECK: store i32 %x.0, ptr %_0, align 8
// CHECK: store i32 %x.1, ptr %0, align 4
// CHECK: %[[R:.+]] = load i64, ptr %_0, align 8
// CHECK: ret i64 %[[R]]
transmute(x)
}

Expand Down
2 changes: 1 addition & 1 deletion tests/codegen/personality_lifetimes.rs
Original file line number Diff line number Diff line change
Expand Up @@ -24,7 +24,7 @@ pub fn test() {
let _s = S;
// Check that the personality slot alloca gets a lifetime start in each cleanup block, not just
// in the first one.
// CHECK: [[SLOT:%[0-9]+]] = alloca { ptr, i32 }
// CHECK: [[SLOT:%[0-9]+]] = alloca { ptr, i32{{.*}} }
// CHECK-LABEL: cleanup:
// CHECK: call void @llvm.lifetime.start.{{.*}}({{.*}})
// CHECK-LABEL: cleanup1:
Expand Down
5 changes: 2 additions & 3 deletions tests/codegen/refs.rs
Original file line number Diff line number Diff line change
Expand Up @@ -13,9 +13,8 @@ pub fn helper(_: usize) {
pub fn ref_dst(s: &[u8]) {
// We used to generate an extra alloca and memcpy to ref the dst, so check that we copy
// directly to the alloca for "x"
// CHECK: [[X0:%[0-9]+]] = getelementptr inbounds { ptr, [[USIZE]] }, {{.*}} %x, i32 0, i32 0
// CHECK: store ptr %s.0, {{.*}} [[X0]]
// CHECK: [[X1:%[0-9]+]] = getelementptr inbounds { ptr, [[USIZE]] }, {{.*}} %x, i32 0, i32 1
// CHECK: store ptr %s.0, {{.*}} %x
// CHECK: [[X1:%[0-9]+]] = getelementptr inbounds i8, {{.*}} %x, {{i32 4|i64 8}}
// CHECK: store [[USIZE]] %s.1, {{.*}} [[X1]]

let x = &*s;
Expand Down
8 changes: 4 additions & 4 deletions tests/codegen/scalar-pair-bool.rs
Original file line number Diff line number Diff line change
Expand Up @@ -2,25 +2,25 @@

#![crate_type = "lib"]

// CHECK: define{{.*}}{ i8, i8 } @pair_bool_bool(i1 noundef zeroext %pair.0, i1 noundef zeroext %pair.1)
// CHECK: define{{.*}}{ i1, i1 } @pair_bool_bool(i1 noundef zeroext %pair.0, i1 noundef zeroext %pair.1)
#[no_mangle]
pub fn pair_bool_bool(pair: (bool, bool)) -> (bool, bool) {
pair
}

// CHECK: define{{.*}}{ i8, i32 } @pair_bool_i32(i1 noundef zeroext %pair.0, i32 noundef %pair.1)
// CHECK: define{{.*}}{ i1, i32 } @pair_bool_i32(i1 noundef zeroext %pair.0, i32 noundef %pair.1)
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Oh, this is amazing! 🎉

Should save truncs in the uses that (since there's no trunc nuw) I've sometimes seem cause poor codegen.

#[no_mangle]
pub fn pair_bool_i32(pair: (bool, i32)) -> (bool, i32) {
pair
}

// CHECK: define{{.*}}{ i32, i8 } @pair_i32_bool(i32 noundef %pair.0, i1 noundef zeroext %pair.1)
// CHECK: define{{.*}}{ i32, i1 } @pair_i32_bool(i32 noundef %pair.0, i1 noundef zeroext %pair.1)
#[no_mangle]
pub fn pair_i32_bool(pair: (i32, bool)) -> (i32, bool) {
pair
}

// CHECK: define{{.*}}{ i8, i8 } @pair_and_or(i1 noundef zeroext %_1.0, i1 noundef zeroext %_1.1)
// CHECK: define{{.*}}{ i1, i1 } @pair_and_or(i1 noundef zeroext %_1.0, i1 noundef zeroext %_1.1)
#[no_mangle]
pub fn pair_and_or((a, b): (bool, bool)) -> (bool, bool) {
// Make sure it can operate directly on the unpacked args
Expand Down
8 changes: 4 additions & 4 deletions tests/codegen/slice-iter-nonnull.rs
Original file line number Diff line number Diff line change
Expand Up @@ -15,7 +15,7 @@
// CHECK-LABEL: @slice_iter_next(
#[no_mangle]
pub fn slice_iter_next<'a>(it: &mut std::slice::Iter<'a, u32>) -> Option<&'a u32> {
// CHECK: %[[ENDP:.+]] = getelementptr{{.+}}ptr %it,{{.+}} 1
// CHECK: %[[ENDP:.+]] = getelementptr inbounds i8, ptr %it, {{i32 4|i64 8}}
// CHECK: %[[END:.+]] = load ptr, ptr %[[ENDP]]
// CHECK-SAME: !nonnull
// CHECK-SAME: !noundef
Expand All @@ -32,7 +32,7 @@ pub fn slice_iter_next<'a>(it: &mut std::slice::Iter<'a, u32>) -> Option<&'a u32
// CHECK-LABEL: @slice_iter_next_back(
#[no_mangle]
pub fn slice_iter_next_back<'a>(it: &mut std::slice::Iter<'a, u32>) -> Option<&'a u32> {
// CHECK: %[[ENDP:.+]] = getelementptr{{.+}}ptr %it,{{.+}} 1
// CHECK: %[[ENDP:.+]] = getelementptr inbounds i8, ptr %it, {{i32 4|i64 8}}
// CHECK: %[[END:.+]] = load ptr, ptr %[[ENDP]]
// CHECK-SAME: !nonnull
// CHECK-SAME: !noundef
Expand Down Expand Up @@ -84,7 +84,7 @@ pub fn slice_iter_mut_new(slice: &mut [u32]) -> std::slice::IterMut<'_, u32> {
// CHECK-LABEL: @slice_iter_is_empty
#[no_mangle]
pub fn slice_iter_is_empty(it: &std::slice::Iter<'_, u32>) -> bool {
// CHECK: %[[ENDP:.+]] = getelementptr{{.+}}ptr %it,{{.+}} 1
// CHECK: %[[ENDP:.+]] = getelementptr inbounds i8, ptr %it, {{i32 4|i64 8}}
// CHECK: %[[END:.+]] = load ptr, ptr %[[ENDP]]
// CHECK-SAME: !nonnull
// CHECK-SAME: !noundef
Expand All @@ -100,7 +100,7 @@ pub fn slice_iter_is_empty(it: &std::slice::Iter<'_, u32>) -> bool {
// CHECK-LABEL: @slice_iter_len
#[no_mangle]
pub fn slice_iter_len(it: &std::slice::Iter<'_, u32>) -> usize {
// CHECK: %[[ENDP:.+]] = getelementptr{{.+}}ptr %it,{{.+}} 1
// CHECK: %[[ENDP:.+]] = getelementptr inbounds i8, ptr %it, {{i32 4|i64 8}}
// CHECK: %[[END:.+]] = load ptr, ptr %[[ENDP]]
// CHECK-SAME: !nonnull
// CHECK-SAME: !noundef
Expand Down
2 changes: 1 addition & 1 deletion tests/codegen/zst-offset.rs
Original file line number Diff line number Diff line change
Expand Up @@ -22,7 +22,7 @@ pub fn scalar_layout(s: &(u64, ())) {
// CHECK-LABEL: @scalarpair_layout
#[no_mangle]
pub fn scalarpair_layout(s: &(u64, u32, ())) {
// CHECK: getelementptr i8, {{.+}}, [[USIZE]] 12
// CHECK: getelementptr inbounds i8, {{.+}}, [[USIZE]] 12
let x = &s.2;
witness(&x); // keep variable in an alloca
}
Expand Down