Skip to content

Do not generate allocations for zero sized allocations #63635

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

Merged
merged 3 commits into from
Aug 18, 2019
Merged

Do not generate allocations for zero sized allocations #63635

Changes from 1 commit
Commits
Show all changes
3 commits
Select commit Hold shift + click to select a range
1fb854a
Do not generate allocations for zero sized allocations
oli-obk Aug 16, 2019
ab949fd
Cast only where necessary
oli-obk Aug 17, 2019
1ea88a8
Add tests
oli-obk Aug 17, 2019
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
21 changes: 13 additions & 8 deletions src/librustc_codegen_llvm/common.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -333,14 +333,19 @@ impl ConstMethods<'tcx> for CodegenCx<'ll, 'tcx> {
offset: Size,
) -> PlaceRef<'tcx, &'ll Value> {
assert_eq!(alloc.align, layout.align.abi);
let init = const_alloc_to_llvm(self, alloc);
let base_addr = self.static_addr_of(init, alloc.align, None);

let llval = unsafe { llvm::LLVMConstInBoundsGEP(
self.const_bitcast(base_addr, self.type_i8p()),
&self.const_usize(offset.bytes()),
1,
)};
let llval = if layout.size == Size::ZERO {
let llval = self.const_usize(alloc.align.bytes());
unsafe { llvm::LLVMConstIntToPtr(llval, self.type_ptr_to(self.type_i8p())) }
Copy link
Member

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Also this seems like you're creating a i8** instead of i8* (but ideally we'd just go directly to the final type).

} else {
let init = const_alloc_to_llvm(self, alloc);
let base_addr = self.static_addr_of(init, alloc.align, None);

unsafe { llvm::LLVMConstInBoundsGEP(
self.const_bitcast(base_addr, self.type_i8p()),
&self.const_usize(offset.bytes()),
1,
)}
};
let llval = self.const_bitcast(llval, self.type_ptr_to(layout.llvm_type(self)));
Copy link
Member

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Could you move the bitcast to the non-zero-len arm? And compute this final pointer type only once?

PlaceRef::new_sized(llval, layout, alloc.align)
}
Expand Down