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auto merge of #13935 : thestinger/rust/noalias, r=pcwalton 

This was removed because these could alias with `&const T` or `@mut T`
and those are now gone from the language. There are still aliasing
issues within local scopes, but this is correct for function parameters.

This also removes the no-op `noalias` marker on proc (not a pointer) and
leaves out the mention of #6750 because real type-based alias analysis
is not within the scope of best effort usage of the `noalias` attribute.

Test case:

    pub fn foo(x: &mut &mut u32) {
        **x = 5;
        **x = 5;
    }

Before:

    define void @_ZN3foo20h0ce94c9671b0150bdaa4v0.0E(i32** nocapture readonly) unnamed_addr #0 {
    entry-block:
      %1 = load i32** %0, align 8
      store i32 5, i32* %1, align 4
      %2 = load i32** %0, align 8
      store i32 5, i32* %2, align 4
      ret void
    }

After:

    define void @_ZN3foo20h0ce94c9671b0150bdaa4v0.0E(i32** noalias nocapture readonly) unnamed_addr #0 {
    entry-block:
      %1 = load i32** %0, align 8
      store i32 5, i32* %1, align 4
      ret void
    }

Closes #12436
This commit is contained in:
bors 2014-05-05 08:41:39 -07:00
parent ecc18f3444 f62c753b8f
commit 2be738ae36
1 changed files with 11 additions and 11 deletions
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22
src/librustc/middle/trans/base.rs
View File

@ -186,8 +186,6 @@ fn decl_fn(llmod: ModuleRef, name: &str, cc: lib::llvm::CallConv,
}
}
// `~` pointer return values never alias because ownership is transferred
// FIXME #6750 ~Trait cannot be directly marked as
// noalias because the actual object pointer is nested.
ty::ty_uniq(..) // | ty::ty_trait(_, _, ty::UniqTraitStore, _, _)
=> {
unsafe {
@ -258,23 +256,25 @@ pub fn decl_rust_fn(ccx: &CrateContext, has_env: bool,
let llarg = unsafe { llvm::LLVMGetParam(llfn, (offset + i) as c_uint) };
match ty::get(arg_ty).sty {
// `~` pointer parameters never alias because ownership is transferred
// FIXME #6750 ~Trait cannot be directly marked as
// noalias because the actual object pointer is nested.
ty::ty_uniq(..) | // ty::ty_trait(_, _, ty::UniqTraitStore, _, _) |
ty::ty_closure(~ty::ClosureTy {store: ty::UniqTraitStore, ..}) => {
ty::ty_uniq(..) => {
unsafe {
llvm::LLVMAddAttribute(llarg, lib::llvm::NoAliasAttribute as c_uint);
}
},
// When a reference in an argument has no named lifetime, it's
// impossible for that reference to escape this function(ie, be
// returned).
}
// `&mut` pointer parameters never alias other parameters, or mutable global data
ty::ty_rptr(_, mt) if mt.mutbl == ast::MutMutable => {
unsafe {
llvm::LLVMAddAttribute(llarg, lib::llvm::NoAliasAttribute as c_uint);
}
}
// When a reference in an argument has no named lifetime, it's impossible for that
// reference to escape this function (returned or stored beyond the call by a closure).
ty::ty_rptr(ReLateBound(_, BrAnon(_)), _) => {
debug!("marking argument of {} as nocapture because of anonymous lifetime", name);
unsafe {
llvm::LLVMAddAttribute(llarg, lib::llvm::NoCaptureAttribute as c_uint);
}
},
}
_ => {
// For non-immediate arguments the callee gets its own copy of
// the value on the stack, so there are no aliases