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Auto merge of #111768 - oli-obk:pair_const_llvm, r=cjgillot

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Optimize scalar and scalar pair representations loaded from ByRef in llvm

in https://github.com/rust-lang/rust/pull/105653 I noticed that we were generating suboptimal LLVM IR if we had a `ConstValue::ByRef` that could be represented by a `ScalarPair`. Before https://github.com/rust-lang/rust/pull/105653 this is probably rare, but after it, every slice will go down this suboptimal code path that requires LLVM to untangle a bunch of indirections and translate static allocations that are only used once to read a scalar pair from.
This commit is contained in:
bors 2023-05-30 10:31:10 +00:00
commit 3266c36624
6 changed files with 120 additions and 83 deletions
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49
compiler/rustc_codegen_llvm/src/common.rs
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@ -8,16 +8,15 @@ use crate::type_of::LayoutLlvmExt;
use crate::value::Value;
use rustc_ast::Mutability;
use rustc_codegen_ssa::mir::place::PlaceRef;
use rustc_codegen_ssa::traits::*;
use rustc_data_structures::stable_hasher::{Hash128, HashStable, StableHasher};
use rustc_hir::def_id::DefId;
use rustc_middle::bug;
use rustc_middle::mir::interpret::{ConstAllocation, GlobalAlloc, Scalar};
use rustc_middle::ty::layout::{LayoutOf, TyAndLayout};
use rustc_middle::ty::layout::LayoutOf;
use rustc_middle::ty::TyCtxt;
use rustc_session::cstore::{DllCallingConvention, DllImport, PeImportNameType};
use rustc_target::abi::{self, AddressSpace, HasDataLayout, Pointer, Size};
use rustc_target::abi::{self, AddressSpace, HasDataLayout, Pointer};
use rustc_target::spec::Target;
use libc::{c_char, c_uint};
@ -307,38 +306,24 @@ impl<'ll, 'tcx> ConstMethods<'tcx> for CodegenCx<'ll, 'tcx> {
const_alloc_to_llvm(self, alloc)
}
fn from_const_alloc(
&self,
layout: TyAndLayout<'tcx>,
alloc: ConstAllocation<'tcx>,
offset: Size,
) -> PlaceRef<'tcx, &'ll Value> {
let alloc_align = alloc.inner().align;
assert_eq!(alloc_align, layout.align.abi);
let llty = self.type_ptr_to(layout.llvm_type(self));
let llval = if layout.size == Size::ZERO {
let llval = self.const_usize(alloc_align.bytes());
unsafe { llvm::LLVMConstIntToPtr(llval, llty) }
} else {
let init = const_alloc_to_llvm(self, alloc);
let base_addr = self.static_addr_of(init, alloc_align, None);
let llval = unsafe {
llvm::LLVMRustConstInBoundsGEP2(
self.type_i8(),
self.const_bitcast(base_addr, self.type_i8p()),
&self.const_usize(offset.bytes()),
1,
)
};
self.const_bitcast(llval, llty)
};
PlaceRef::new_sized(llval, layout)
}
fn const_ptrcast(&self, val: &'ll Value, ty: &'ll Type) -> &'ll Value {
consts::ptrcast(val, ty)
}
fn const_bitcast(&self, val: &'ll Value, ty: &'ll Type) -> &'ll Value {
self.const_bitcast(val, ty)
}
fn const_ptr_byte_offset(&self, base_addr: Self::Value, offset: abi::Size) -> Self::Value {
unsafe {
llvm::LLVMRustConstInBoundsGEP2(
self.type_i8(),
self.const_bitcast(base_addr, self.type_i8p()),
&self.const_usize(offset.bytes()),
1,
)
}
}
}
/// Get the [LLVM type][Type] of a [`Value`].