Rollup merge of #86652 - nagisa:nagisa/non-leaf-fp, r=petrochenkov

Add support for leaf function frame pointer elimination

This PR adds ability for the target specifications to specify frame
pointer emission type that's not just “always” or “whatever cg decides”.

In particular there's a new mode that allows omission of the frame
pointer for leaf functions (those that don't call any other functions).

We then set this new mode for Aarch64-based Apple targets.

Fixes #86196

compiler/rustc_codegen_llvm/src/attributes.rs

@@ -12,7 +12,7 @@ use rustc_middle::ty::{self, TyCtxt};
 use rustc_session::config::OptLevel;
 use rustc_session::Session;
 use rustc_target::spec::abi::Abi;
-use rustc_target::spec::{SanitizerSet, StackProbeType};
+use rustc_target::spec::{FramePointer, SanitizerSet, StackProbeType};
 
 use crate::attributes;
 use crate::llvm::AttributePlace::Function;
@@ -69,15 +69,25 @@ fn naked(val: &'ll Value, is_naked: bool) {
     Attribute::Naked.toggle_llfn(Function, val, is_naked);
 }
 
-pub fn set_frame_pointer_elimination(cx: &CodegenCx<'ll, '_>, llfn: &'ll Value) {
-    if cx.sess().must_not_eliminate_frame_pointers() {
-        llvm::AddFunctionAttrStringValue(
-            llfn,
-            llvm::AttributePlace::Function,
-            cstr!("frame-pointer"),
-            cstr!("all"),
-        );
+pub fn set_frame_pointer_type(cx: &CodegenCx<'ll, '_>, llfn: &'ll Value) {
+    let mut fp = cx.sess().target.frame_pointer;
+    // "mcount" function relies on stack pointer.
+    // See <https://sourceware.org/binutils/docs/gprof/Implementation.html>.
+    if cx.sess().instrument_mcount() || matches!(cx.sess().opts.cg.force_frame_pointers, Some(true))
+    {
+        fp = FramePointer::Always;
     }
+    let attr_value = match fp {
+        FramePointer::Always => cstr!("all"),
+        FramePointer::NonLeaf => cstr!("non-leaf"),
+        FramePointer::MayOmit => return,
+    };
+    llvm::AddFunctionAttrStringValue(
+        llfn,
+        llvm::AttributePlace::Function,
+        cstr!("frame-pointer"),
+        attr_value,
+    );
 }
 
 /// Tell LLVM what instrument function to insert.
@@ -254,7 +264,7 @@ pub fn from_fn_attrs(cx: &CodegenCx<'ll, 'tcx>, llfn: &'ll Value, instance: ty::
     }
 
     // FIXME: none of these three functions interact with source level attributes.
-    set_frame_pointer_elimination(cx, llfn);
+    set_frame_pointer_type(cx, llfn);
     set_instrument_function(cx, llfn);
     set_probestack(cx, llfn);
 

compiler/rustc_codegen_llvm/src/context.rs

@@ -410,8 +410,8 @@ impl MiscMethods<'tcx> for CodegenCx<'ll, 'tcx> {
         &self.used_statics
     }
 
-    fn set_frame_pointer_elimination(&self, llfn: &'ll Value) {
-        attributes::set_frame_pointer_elimination(self, llfn)
+    fn set_frame_pointer_type(&self, llfn: &'ll Value) {
+        attributes::set_frame_pointer_type(self, llfn)
     }
 
     fn apply_target_cpu_attr(&self, llfn: &'ll Value) {

compiler/rustc_codegen_llvm/src/intrinsic.rs

@@ -674,7 +674,7 @@ fn gen_fn<'ll, 'tcx>(
 ) -> &'ll Value {
     let fn_abi = FnAbi::of_fn_ptr(cx, rust_fn_sig, &[]);
     let llfn = cx.declare_fn(name, &fn_abi);
-    cx.set_frame_pointer_elimination(llfn);
+    cx.set_frame_pointer_type(llfn);
     cx.apply_target_cpu_attr(llfn);
     // FIXME(eddyb) find a nicer way to do this.
     unsafe { llvm::LLVMRustSetLinkage(llfn, llvm::Linkage::InternalLinkage) };