add sret + noalias to the out pointer parameter
This brings Rust in line with how `clang` handles return pointers. Example: pub fn bar() -> [uint, .. 8] { let a = [0, .. 8]; a } Before: ; Function Attrs: nounwind uwtable define void @_ZN3bar17ha4635c6f704bfa334v0.0E([8 x i64]* nocapture, { i64, %tydesc*, i8*, i8*, i8 }* nocapture readnone) #1 { "function top level": %a = alloca [8 x i64], align 8 %2 = bitcast [8 x i64]* %a to i8* call void @llvm.memset.p0i8.i64(i8* %2, i8 0, i64 64, i32 8, i1 false) %3 = bitcast [8 x i64]* %0 to i8* call void @llvm.memcpy.p0i8.p0i8.i64(i8* %3, i8* %2, i64 64, i32 8, i1 false) ret void } After: ; Function Attrs: nounwind uwtable define void @_ZN3bar17ha4635c6f704bfa334v0.0E([8 x i64]* noalias nocapture sret, { i64, %tydesc*, i8*, i8*, i8 }* nocapture readnone) #1 { "function top level": %2 = bitcast [8 x i64]* %0 to i8* call void @llvm.memset.p0i8.i64(i8* %2, i8 0, i64 64, i32 8, i1 false) ret void } Closes #9072 Closes #7298 Closes #9154
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@ -248,6 +248,17 @@ pub fn decl_rust_fn(ccx: &mut CrateContext, inputs: &[ty::t], output: ty::t,
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}
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}
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// The out pointer will never alias with any other pointers, as the object only exists at a
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// language level after the call. It can also be tagged with SRet to indicate that it is
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// guaranteed to point to a usable block of memory for the type.
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if uses_outptr {
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unsafe {
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let outptr = llvm::LLVMGetParam(llfn, 0);
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llvm::LLVMAddAttribute(outptr, lib::llvm::StructRetAttribute as c_uint);
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llvm::LLVMAddAttribute(outptr, lib::llvm::NoAliasAttribute as c_uint);
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}
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}
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llfn
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}
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@ -20,7 +20,7 @@ use std::vec;
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use back::abi;
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use driver::session;
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use lib::llvm::ValueRef;
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use lib::llvm::{ValueRef, NoAliasAttribute, StructRetAttribute};
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use lib::llvm::llvm;
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use metadata::csearch;
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use middle::trans::base;
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@ -707,7 +707,21 @@ pub fn trans_call_inner(in_cx: @mut Block,
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}
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// Invoke the actual rust fn and update bcx/llresult.
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let (llret, b) = base::invoke(bcx, llfn, llargs, []);
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let mut attrs = ~[];
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if type_of::return_uses_outptr(in_cx.tcx(), ret_ty) {
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attrs.push((1, StructRetAttribute));
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}
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match ty::get(ret_ty).sty {
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// `~` pointer return values never alias because ownership is transferred
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ty::ty_uniq(*) |
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ty::ty_evec(_, ty::vstore_uniq) => {
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attrs.push((0, NoAliasAttribute));
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}
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_ => ()
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}
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let (llret, b) = base::invoke(bcx, llfn, llargs, attrs);
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bcx = b;
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llresult = llret;
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@ -497,7 +497,7 @@ pub fn trans_rust_fn_with_foreign_abi(ccx: @mut CrateContext,
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// Rust expects to use an outpointer. If the foreign fn
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// also uses an outpointer, we can reuse it, but the types
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// may vary, so cast first to the Rust type. If the
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// foriegn fn does NOT use an outpointer, we will have to
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// foreign fn does NOT use an outpointer, we will have to
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// alloca some scratch space on the stack.
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match foreign_outptr {
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Some(llforeign_outptr) => {
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