From c2fd26a115645c92537719b1a04270e1ba727cbf Mon Sep 17 00:00:00 2001 From: Nikita Popov Date: Fri, 15 Dec 2023 12:14:39 +0100 Subject: Separate immediate and in-memory ScalarPair representation Currently, we assume that ScalarPair is always represented using a two-element struct, both as an immediate value and when stored in memory. This currently works fairly well, but runs into problems with https://github.com/rust-lang/rust/pull/116672, where a ScalarPair involving an i128 type can no longer be represented as a two-element struct in memory. For example, the tuple `(i32, i128)` needs to be represented in-memory as `{ i32, [3 x i32], i128 }` to satisfy alignment requirement. Using `{ i32, i128 }` instead will result in the second element being stored at the wrong offset (prior to LLVM 18). Resolve this issue by no longer requiring that the immediate and in-memory type for ScalarPair are the same. The in-memory type will now look the same as for normal struct types (and will include padding filler and similar), while the immediate type stays a simple two-element struct type. This also means that booleans in immediate ScalarPair are now represented as i1 rather than i8, just like we do everywhere else. The core change here is to llvm_type (which now treats ScalarPair as a normal struct) and immediate_llvm_type (which returns the two-element struct that llvm_type used to produce). The rest is fixing things up to no longer assume these are the same. In particular, this switches places that try to get pointers to the ScalarPair elements to use byte-geps instead of struct-geps. --- compiler/rustc_codegen_llvm/src/abi.rs | 4 ++-- compiler/rustc_codegen_llvm/src/builder.rs | 11 +++++++-- compiler/rustc_codegen_llvm/src/intrinsic.rs | 5 +++- compiler/rustc_codegen_llvm/src/type_of.rs | 34 ++++++++++++++++------------ 4 files changed, 35 insertions(+), 19 deletions(-) (limited to 'compiler/rustc_codegen_llvm/src') diff --git a/compiler/rustc_codegen_llvm/src/abi.rs b/compiler/rustc_codegen_llvm/src/abi.rs index 97dc401251c..0718bebb31b 100644 --- a/compiler/rustc_codegen_llvm/src/abi.rs +++ b/compiler/rustc_codegen_llvm/src/abi.rs @@ -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; @@ -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); } } diff --git a/compiler/rustc_codegen_llvm/src/builder.rs b/compiler/rustc_codegen_llvm/src/builder.rs index f4b9296dbbd..70e81662c30 100644 --- a/compiler/rustc_codegen_llvm/src/builder.rs +++ b/compiler/rustc_codegen_llvm/src/builder.rs @@ -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 + } 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); diff --git a/compiler/rustc_codegen_llvm/src/intrinsic.rs b/compiler/rustc_codegen_llvm/src/intrinsic.rs index 58e68a64907..430621d74fe 100644 --- a/compiler/rustc_codegen_llvm/src/intrinsic.rs +++ b/compiler/rustc_codegen_llvm/src/intrinsic.rs @@ -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); + } + return; } sym::volatile_store => { let dst = args[0].deref(self.cx()); diff --git a/compiler/rustc_codegen_llvm/src/type_of.rs b/compiler/rustc_codegen_llvm/src/type_of.rs index 624ce6d8813..adedaf7eccd 100644 --- a/compiler/rustc_codegen_llvm/src/type_of.rs +++ b/compiler/rustc_codegen_llvm/src/type_of.rs @@ -26,16 +26,8 @@ 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 { .. } => {} + // Treat ScalarPair like a normal aggregate for the purposes of in-memory representation. + Abi::Uninhabited | Abi::Aggregate { .. } | Abi::ScalarPair(..) => {} } let name = match layout.ty.kind() { @@ -275,11 +267,25 @@ 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) } -- cgit 1.4.1-3-g733a5 From 8e64fc94d895b570e80db8edc3e3ef265e19db8c Mon Sep 17 00:00:00 2001 From: Nikita Popov Date: Tue, 2 Jan 2024 14:41:08 +0100 Subject: Address review comments --- compiler/rustc_codegen_llvm/src/type_of.rs | 1 - compiler/rustc_codegen_ssa/src/mir/place.rs | 12 +++++------- tests/codegen/zst-offset.rs | 2 +- 3 files changed, 6 insertions(+), 9 deletions(-) (limited to 'compiler/rustc_codegen_llvm/src') diff --git a/compiler/rustc_codegen_llvm/src/type_of.rs b/compiler/rustc_codegen_llvm/src/type_of.rs index adedaf7eccd..c8bf8b9514a 100644 --- a/compiler/rustc_codegen_llvm/src/type_of.rs +++ b/compiler/rustc_codegen_llvm/src/type_of.rs @@ -26,7 +26,6 @@ fn uncached_llvm_type<'a, 'tcx>( let element = layout.scalar_llvm_type_at(cx, element); return cx.type_vector(element, count); } - // Treat ScalarPair like a normal aggregate for the purposes of in-memory representation. Abi::Uninhabited | Abi::Aggregate { .. } | Abi::ScalarPair(..) => {} } diff --git a/compiler/rustc_codegen_ssa/src/mir/place.rs b/compiler/rustc_codegen_ssa/src/mir/place.rs index 40d6c7eb50c..73c08e2ca61 100644 --- a/compiler/rustc_codegen_ssa/src/mir/place.rs +++ b/compiler/rustc_codegen_ssa/src/mir/place.rs @@ -108,19 +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. + Abi::ScalarPair(..) => { + // FIXME(nikic): Generate this for all ABIs. bx.inbounds_gep(bx.type_i8(), self.llval, &[bx.const_usize(offset.bytes())]) } - 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 `{:#?}`", diff --git a/tests/codegen/zst-offset.rs b/tests/codegen/zst-offset.rs index cef4b9bdaaf..56dfd96ab2c 100644 --- a/tests/codegen/zst-offset.rs +++ b/tests/codegen/zst-offset.rs @@ -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 } -- cgit 1.4.1-3-g733a5