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Move shared offload globals and define per-kernel globals once #149788

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Move shared offload globals and define per-kernel globals once #149788

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3e4944d
Split runtime global logic and cache kernel specific one
Sa4dUs Dec 8, 2025
8bafb63
Remove outdated comment
Sa4dUs Dec 8, 2025
04c2d2b
Remove `region_id` unnamed attr
Sa4dUs Dec 18, 2025
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3 changes: 1 addition & 2 deletions compiler/rustc_codegen_llvm/src/back/write.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -710,8 +710,7 @@ pub(crate) unsafe fn llvm_optimize(
if cgcx.target_is_like_gpu && config.offload.contains(&config::Offload::Enable) {
let cx =
SimpleCx::new(module.module_llvm.llmod(), module.module_llvm.llcx, cgcx.pointer_size);
// For now we only support up to 10 kernels named kernel_0 ... kernel_9, a follow-up PR is
// introducing a proper offload intrinsic to solve this limitation.

for func in cx.get_functions() {
let offload_kernel = "offload-kernel";
if attributes::has_string_attr(func, offload_kernel) {
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16 changes: 15 additions & 1 deletion compiler/rustc_codegen_llvm/src/base.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -23,13 +23,14 @@ use rustc_middle::dep_graph;
use rustc_middle::middle::codegen_fn_attrs::{CodegenFnAttrs, SanitizerFnAttrs};
use rustc_middle::mir::mono::Visibility;
use rustc_middle::ty::TyCtxt;
use rustc_session::config::DebugInfo;
use rustc_session::config::{DebugInfo, Offload};
use rustc_span::Symbol;
use rustc_target::spec::SanitizerSet;

use super::ModuleLlvm;
use crate::attributes;
use crate::builder::Builder;
use crate::builder::gpu_offload::OffloadGlobals;
use crate::context::CodegenCx;
use crate::llvm::{self, Value};

Expand Down Expand Up @@ -85,6 +86,19 @@ pub(crate) fn compile_codegen_unit(
let llvm_module = ModuleLlvm::new(tcx, cgu_name.as_str());
{
let mut cx = CodegenCx::new(tcx, cgu, &llvm_module);

// Declare and store globals shared by all offload kernels
//
// These globals are left in the LLVM-IR host module so all kernels can access them.
// They are necessary for correct offload execution. We do this here to simplify the
// `offload` intrinsic, avoiding the need for tracking whether it's the first
// intrinsic call or not.
if cx.sess().opts.unstable_opts.offload.contains(&Offload::Enable)
&& !cx.sess().target.is_like_gpu
{
cx.offload_globals.replace(Some(OffloadGlobals::declare(&cx)));
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@Sa4dUs Sa4dUs Dec 8, 2025

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i'm a bit unsure about this location. we could also cache these globals and generate them on the first intrinsic call, but that felt like overloading intrinsic codegen a bit too much

i don't have a strong opinion though, so happy to go with whatever u think is best

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@ZuseZ4 ZuseZ4 Dec 19, 2025

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I'd also prefer if the intrinsics stay simple and don't need global context about whether they're the first intrinsic or not.

The location seems fine, but can you leave a comment explaining that we have to leave a bunch of globals in the LLVM-IR host module? Similar to e.g. objective-c below. Otherwise lgtm.

}

let mono_items = cx.codegen_unit.items_in_deterministic_order(cx.tcx);
for &(mono_item, data) in &mono_items {
mono_item.predefine::<Builder<'_, '_, '_>>(
Expand Down
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