Auto merge of #92419 - erikdesjardins:coldland, r=nagisa

Mark drop calls in landing pads `cold` instead of `noinline`

Now that deferred inlining has been disabled in LLVM (#92110), this shouldn't cause catastrophic size blowup.

I confirmed that the test cases from https://github.com/rust-lang/rust/issues/41696#issuecomment-298696944 still compile quickly (<1s) after this change. ~Although note that I wasn't able to reproduce the original issue using a recent rustc/llvm with deferred inlining enabled, so those tests may no longer be representative. I was also unable to create a modified test case that reproduced the original issue.~ (edit: I reproduced it on CI by accident--the first commit timed out on the LLVM 12 builder, because I forgot to make it conditional on LLVM version)

r? `@nagisa`
cc `@arielb1` (this effectively reverts #42771 "mark calls in the unwind path as !noinline")
cc `@RalfJung` (fixes #46515)

edit: also fixes #87055

3 files changed, 17 insertions, 2 deletions

diff --git a/compiler/rustc_codegen_llvm/src/builder.rs b/compiler/rustc_codegen_llvm/src/builder.rs
index 8c3054b23ff..5217fa2758f 100644
--- a/compiler/rustc_codegen_llvm/src/builder.rs
+++ b/compiler/rustc_codegen_llvm/src/builder.rs
@@ -1201,8 +1201,15 @@ impl<'a, 'll, 'tcx> BuilderMethods<'a, 'tcx> for Builder<'a, 'll, 'tcx> {
         unsafe { llvm::LLVMBuildZExt(self.llbuilder, val, dest_ty, UNNAMED) }
     }
 
-    fn do_not_inline(&mut self, llret: &'ll Value) {
-        llvm::Attribute::NoInline.apply_callsite(llvm::AttributePlace::Function, llret);
+    fn apply_attrs_to_cleanup_callsite(&mut self, llret: &'ll Value) {
+        // Cleanup is always the cold path.
+        llvm::Attribute::Cold.apply_callsite(llvm::AttributePlace::Function, llret);
+
+        // In LLVM versions with deferred inlining (currently, system LLVM < 14),
+        // inlining drop glue can lead to exponential size blowup, see #41696 and #92110.
+        if !llvm_util::is_rust_llvm() && llvm_util::get_version() < (14, 0, 0) {
+            llvm::Attribute::NoInline.apply_callsite(llvm::AttributePlace::Function, llret);
+        }
     }
 }
 
diff --git a/compiler/rustc_codegen_llvm/src/llvm/ffi.rs b/compiler/rustc_codegen_llvm/src/llvm/ffi.rs
index 9c05a9d7142..6450b7490bd 100644
--- a/compiler/rustc_codegen_llvm/src/llvm/ffi.rs
+++ b/compiler/rustc_codegen_llvm/src/llvm/ffi.rs
@@ -1902,6 +1902,8 @@ extern "C" {
     pub fn LLVMRustVersionMinor() -> u32;
     pub fn LLVMRustVersionPatch() -> u32;
 
+    pub fn LLVMRustIsRustLLVM() -> bool;
+
     pub fn LLVMRustAddModuleFlag(M: &Module, name: *const c_char, value: u32);
 
     pub fn LLVMRustMetadataAsValue<'a>(C: &'a Context, MD: &'a Metadata) -> &'a Value;
diff --git a/compiler/rustc_codegen_llvm/src/llvm_util.rs b/compiler/rustc_codegen_llvm/src/llvm_util.rs
index 71834b20fb7..d49df29f453 100644
--- a/compiler/rustc_codegen_llvm/src/llvm_util.rs
+++ b/compiler/rustc_codegen_llvm/src/llvm_util.rs
@@ -223,6 +223,12 @@ pub fn get_version() -> (u32, u32, u32) {
     }
 }
 
+/// Returns `true` if this LLVM is Rust's bundled LLVM (and not system LLVM).
+pub fn is_rust_llvm() -> bool {
+    // Can be called without initializing LLVM
+    unsafe { llvm::LLVMRustIsRustLLVM() }
+}
+
 pub fn print_passes() {
     // Can be called without initializing LLVM
     unsafe {