Skip to content

[ICF] Add a NOP after branch in ICF thunk to improve debugability #154986

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Closed
wants to merge 7 commits into from
Closed

[ICF] Add a NOP after branch in ICF thunk to improve debugability #154986

Show file tree
Hide file tree
Changes from 6 commits
Commits
Show all changes
7 commits
Select commit Hold shift + click to select a range
35082de
[ICF] Add a NOP after branch in ICF thunk to improve debugability
DataCorrupted Aug 22, 2025
3d9e686
Update comment and test
DataCorrupted Aug 22, 2025
decd078
Dont emit for single line functions
DataCorrupted Aug 22, 2025
261a8cf
Update test
DataCorrupted Aug 22, 2025
fd8a30b
Update test
DataCorrupted Aug 23, 2025
5aa87a3
Don't emit LLVM_stmt_seq if there's only one inst in the function
DataCorrupted Aug 25, 2025
07c2546
Update test
DataCorrupted Aug 25, 2025
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
9 changes: 8 additions & 1 deletion lld/MachO/Arch/ARM64.cpp
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -173,9 +173,16 @@ void ARM64::populateThunk(InputSection *thunk, Symbol *funcSym) {
/*offset=*/0, /*addend=*/0,
/*referent=*/funcSym);
}
// Just a single direct branch to the target function.
// Just a single direct branch to the target function and a nop.
// The nop will improve the debuggability.
//
// Debug lines in DWARF does not recognize one-instruction sequence, and this
// thunk will be merged into other sequences if it only had one instruction.
// Adding a nop after the branch has no runtime cost, and little size impact,
// but it would make DWARF linker and debuggers happier.
static constexpr uint32_t icfSafeThunkCode[] = {
0x14000000, // 08: b target
0xD503201F, // 0c: nop
};

void ARM64::initICFSafeThunkBody(InputSection *thunk, Symbol *targetSym) const {
Expand Down
Loading
Loading