tests: add regression test for #135332

Issue: #135332

Author: jieyouxu

tests/run-make/llvm-location-discriminator-limit-dummy-span/main.rs

@@ -0,0 +1,3 @@
+fn main() {
+    other::big_function();
+}

tests/run-make/llvm-location-discriminator-limit-dummy-span/other.rs

@@ -0,0 +1 @@
+proc::declare_big_function!();

tests/run-make/llvm-location-discriminator-limit-dummy-span/proc.rs

@@ -0,0 +1,7 @@
+extern crate proc_macro;
+use proc_macro::TokenStream;
+
+#[proc_macro]
+pub fn declare_big_function(_input: TokenStream) -> TokenStream {
+    include_str!("./generated.rs").parse().unwrap()
+}

tests/run-make/llvm-location-discriminator-limit-dummy-span/rmake.rs

@@ -0,0 +1,58 @@
+//! Regression test for <https://github.com/rust-lang/rust/issues/135332>.
+//!
+//! We can't simply drop debuginfo location spans when LLVM's location discriminator value limit is
+//! reached. Otherwise, with `-Z verify-llvm-ir` and fat LTO, LLVM will report a broken module for
+//!
+//! ```text
+//! inlinable function call in a function with debug info must have a !dbg location
+//! ```
+
+//@ ignore-cross-compile
+//@ needs-dynamic-linking
+//@ only-nightly: requires unstable rustc flag
+
+#![deny(warnings)]
+
+use run_make_support::{dynamic_lib_name, rfs, rust_lib_name, rustc};
+
+// Generate a program that has a *lot*
+fn generate_program(n: u32) -> String {
+    let mut program = String::from("pub type BigType = Vec<Vec<String>>;\n\n");
+    program.push_str("pub fn big_function() -> BigType {\n");
+    program.push_str("    vec![\n");
+    for i in 1..=n {
+        program.push_str(&format!("vec![\"string{}\".to_owned()],\n", i));
+    }
+    program.push_str("    ]\n");
+    program.push_str("}\n");
+    program
+}
+
+fn main() {
+    // The reported threshold is around 1366, but let's bump it to around 1500 to be less sensitive.
+    rfs::write("generated.rs", generate_program(1500));
+
+    rustc()
+        .input("proc.rs")
+        .crate_type("proc-macro")
+        .edition("2021")
+        .arg("-Cdebuginfo=line-tables-only")
+        .run();
+    rustc()
+        .extern_("proc", dynamic_lib_name("proc"))
+        .input("other.rs")
+        .crate_type("rlib")
+        .edition("2021")
+        .opt_level("3")
+        .arg("-Cdebuginfo=line-tables-only")
+        .run();
+    rustc()
+        .extern_("other", rust_lib_name("other"))
+        .input("main.rs")
+        .edition("2021")
+        .opt_level("3")
+        .arg("-Cdebuginfo=line-tables-only")
+        .arg("-Clto=fat")
+        .arg("-Zverify-llvm-ir")
+        .run();
+}