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add sret + noalias to the out pointer parameter #9100

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add sret + noalias to the out pointer parameter #9100

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12 changes: 12 additions & 0 deletions src/librustc/middle/trans/base.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1618,6 +1618,18 @@ pub fn new_fn_ctxt_w_id(ccx: @mut CrateContext,
}
};
let uses_outptr = type_of::return_uses_outptr(ccx.tcx, substd_output_type);

// The out pointer will never alias with any other pointers, as the object only exists at a
// language level after the call. It can also be tagged with SRet to indicate that it is
// guaranteed to point to a usable block of memory for the type.
if uses_outptr {
unsafe {
let outptr = llvm::LLVMGetParam(llfndecl, 0);
llvm::LLVMAddAttribute(outptr, lib::llvm::StructRetAttribute as c_uint);
llvm::LLVMAddAttribute(outptr, lib::llvm::NoAliasAttribute as c_uint);
}
}

let debug_context = debuginfo::create_function_debug_context(ccx, id, param_substs, llfndecl);

let fcx = @mut FunctionContext {
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