Pass LargeDataThreshold to LLVM module IR

compiler/rustc_codegen_llvm/src/context.rs

@@ -282,6 +282,13 @@ pub(crate) unsafe fn create_module<'ll>(
         llvm::LLVMRustSetModuleCodeModel(llmod, to_llvm_code_model(sess.code_model()));
     }
 
+    let large_data_threshold = sess.opts.unstable_opts.large_data_threshold.unwrap_or(0);
+    if large_data_threshold != 0 {
+        unsafe {
+            llvm::LLVMRustSetModuleLargeDataThreshold(llmod, large_data_threshold);
+        }
+    }
+
     // If skipping the PLT is enabled, we need to add some module metadata
     // to ensure intrinsic calls don't use it.
     if !sess.needs_plt() {

compiler/rustc_codegen_llvm/src/llvm/ffi.rs

@@ -2508,6 +2508,7 @@ unsafe extern "C" {
     pub(crate) fn LLVMRustSetModulePICLevel(M: &Module);
     pub(crate) fn LLVMRustSetModulePIELevel(M: &Module);
     pub(crate) fn LLVMRustSetModuleCodeModel(M: &Module, Model: CodeModel);
+    pub(crate) fn LLVMRustSetModuleLargeDataThreshold(M: &Module, Threshold: u64);
     pub(crate) fn LLVMRustBufferPtr(p: &Buffer) -> *const u8;
     pub(crate) fn LLVMRustBufferLen(p: &Buffer) -> usize;
     pub(crate) fn LLVMRustBufferFree(p: &'static mut Buffer);

compiler/rustc_llvm/llvm-wrapper/PassWrapper.cpp

@@ -1179,6 +1179,11 @@ extern "C" void LLVMRustSetModuleCodeModel(LLVMModuleRef M,
   unwrap(M)->setCodeModel(*CM);
 }
 
+extern "C" void LLVMRustSetModuleLargeDataThreshold(LLVMModuleRef M,
+                                                    uint64_t Threshold) {
+  unwrap(M)->setLargeDataThreshold(Threshold);
+}
+
 // Here you'll find an implementation of ThinLTO as used by the Rust compiler
 // right now. This ThinLTO support is only enabled on "recent ish" versions of
 // LLVM, and otherwise it's just blanket rejected from other compilers.

tests/codegen-llvm/large_data_threshold.rs

@@ -0,0 +1,9 @@
+//@ only-x86_64
+//@ revisions: DEFAULT EXPLICIT
+//@[DEFAULT] compile-flags: -C code-model=medium
+//@[EXPLICIT] compile-flags: -C code-model=medium -Z large-data-threshold=1024
+
+#![crate_type = "lib"]
+
+// DEFAULT-NOT: !"Large Data Threshold"
+// EXPLICIT: !{{[0-9]+}} = !{i32 1, !"Large Data Threshold", i64 1024}