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Remove noalias on return values #22018

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Remove noalias on return values #22018

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18 changes: 2 additions & 16 deletions src/librustc_trans/trans/base.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -2490,29 +2490,15 @@ pub fn get_fn_llvm_attributes<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>, fn_ty: Ty<
if type_of::return_uses_outptr(ccx, ret_ty) {
let llret_sz = llsize_of_real(ccx, type_of::type_of(ccx, ret_ty));

// The outptr can be noalias and nocapture because it's entirely
// invisible to the program. We also know it's nonnull as well
// as how many bytes we can dereference
// The outptr can be nocapture because it's entirely invisible to the program. We also
// know it's nonnull as well as how many bytes we can dereference
attrs.arg(1, llvm::StructRetAttribute)
.arg(1, llvm::NoAliasAttribute)
.arg(1, llvm::NoCaptureAttribute)
.arg(1, llvm::DereferenceableAttribute(llret_sz));

// Add one more since there's an outptr
first_arg_offset += 1;
} else {
// The `noalias` attribute on the return value is useful to a
// function ptr caller.
match ret_ty.sty {
// `~` pointer return values never alias because ownership
// is transferred
ty::ty_uniq(it) if !common::type_is_sized(ccx.tcx(), it) => {}
ty::ty_uniq(_) => {
attrs.ret(llvm::NoAliasAttribute);
}
_ => {}
}

// We can also mark the return value as `dereferenceable` in certain cases
match ret_ty.sty {
// These are not really pointers but pairs, (pointer, len)
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8 changes: 3 additions & 5 deletions src/librustc_trans/trans/foreign.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -336,11 +336,9 @@ pub fn trans_native_call<'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
if fn_type.ret_ty.is_indirect() {
let llret_sz = machine::llsize_of_real(ccx, fn_type.ret_ty.ty);

// The outptr can be noalias and nocapture because it's entirely
// invisible to the program. We also know it's nonnull as well
// as how many bytes we can dereference
attrs.arg(1, llvm::NoAliasAttribute)
.arg(1, llvm::NoCaptureAttribute)
// The outptr can be nocapture because it's entirely invisible to the program. We also know
// it's nonnull as well as how many bytes we can dereference
attrs.arg(1, llvm::NoCaptureAttribute)
.arg(1, llvm::DereferenceableAttribute(llret_sz));
};

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