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Add support for leaf fn frame pointer elimination

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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
This commit is contained in:
Simonas Kazlauskas 2021-06-26 23:53:35 +03:00
parent 3ddb78a346
commit 9b67cba4f6
24 changed files with 149 additions and 60 deletions
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30
compiler/rustc_codegen_llvm/src/attributes.rs
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@ -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);