Rollup merge of #127779 - momvart:should_codegen_hook, r=cjgillot

Add a hook for `should_codegen_locally`

This PR lifts the module-local function `should_codegen_locally` to `TyCtxt` as a hook.
In addition to monomorphization, this function is used for checking the dependency of `compiler_builtins` on other libraries. Moving this function to the hooks also makes overriding it possible for the tools that use the rustc interface.

2 files changed, 29 insertions, 2 deletions

diff --git a/compiler/rustc_codegen_ssa/src/base.rs b/compiler/rustc_codegen_ssa/src/base.rs
index 137f14fe706..399ac485850 100644
--- a/compiler/rustc_codegen_ssa/src/base.rs
+++ b/compiler/rustc_codegen_ssa/src/base.rs
@@ -806,6 +806,34 @@ pub fn codegen_crate<B: ExtraBackendMethods>(
     ongoing_codegen
 }
 
+/// Returns whether a call from the current crate to the [`Instance`] would produce a call
+/// from `compiler_builtins` to a symbol the linker must resolve.
+///
+/// Such calls from `compiler_bultins` are effectively impossible for the linker to handle. Some
+/// linkers will optimize such that dead calls to unresolved symbols are not an error, but this is
+/// not guaranteed. So we used this function in codegen backends to ensure we do not generate any
+/// unlinkable calls.
+///
+/// Note that calls to LLVM intrinsics are uniquely okay because they won't make it to the linker.
+pub fn is_call_from_compiler_builtins_to_upstream_monomorphization<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    instance: Instance<'tcx>,
+) -> bool {
+    fn is_llvm_intrinsic(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
+        if let Some(name) = tcx.codegen_fn_attrs(def_id).link_name {
+            name.as_str().starts_with("llvm.")
+        } else {
+            false
+        }
+    }
+
+    let def_id = instance.def_id();
+    !def_id.is_local()
+        && tcx.is_compiler_builtins(LOCAL_CRATE)
+        && !is_llvm_intrinsic(tcx, def_id)
+        && !tcx.should_codegen_locally(instance)
+}
+
 impl CrateInfo {
     pub fn new(tcx: TyCtxt<'_>, target_cpu: String) -> CrateInfo {
         let crate_types = tcx.crate_types().to_vec();
diff --git a/compiler/rustc_codegen_ssa/src/mir/block.rs b/compiler/rustc_codegen_ssa/src/mir/block.rs
index 6a5525dc2b3..c9c8f02c491 100644
--- a/compiler/rustc_codegen_ssa/src/mir/block.rs
+++ b/compiler/rustc_codegen_ssa/src/mir/block.rs
@@ -3,7 +3,7 @@ use super::operand::OperandValue::{Immediate, Pair, Ref, ZeroSized};
 use super::place::{PlaceRef, PlaceValue};
 use super::{CachedLlbb, FunctionCx, LocalRef};
 
-use crate::base;
+use crate::base::{self, is_call_from_compiler_builtins_to_upstream_monomorphization};
 use crate::common::{self, IntPredicate};
 use crate::errors::CompilerBuiltinsCannotCall;
 use crate::meth;
@@ -18,7 +18,6 @@ use rustc_middle::ty::layout::{HasTyCtxt, LayoutOf, ValidityRequirement};
 use rustc_middle::ty::print::{with_no_trimmed_paths, with_no_visible_paths};
 use rustc_middle::ty::{self, Instance, Ty};
 use rustc_middle::{bug, span_bug};
-use rustc_monomorphize::is_call_from_compiler_builtins_to_upstream_monomorphization;
 use rustc_session::config::OptLevel;
 use rustc_span::{source_map::Spanned, sym, Span};
 use rustc_target::abi::call::{ArgAbi, FnAbi, PassMode, Reg};