rjmccall added inline comments.
================
Comment at: lib/CodeGen/CGCall.cpp:3851
+ ->getType()
+ ->getPointerAddressSpace();
const unsigned ArgAddrSpace =
----------------
yaxunl wrote:
> rjmccall wrote:
> > Hmm. Is there actually a test case where Addr.getType()->getAddressSpace()
> > is not the lowering of LangAS::Default? The correctness of the
> > performAddrSpaceCast call you make depends on that.
> >
> > If there isn't, I think it would be better to add a target hook to attempt
> > to peephole an addrspace cast:
> > llvm::Value *tryPeepholeAddrSpaceCast(llvm::Value*, unsigned valueAS,
> > unsigned targetAS);
> >
> > And then you can just do
> > bool HasAddrSpaceMismatch = CGM.getASTAllocaAddrSpace() !=
> > LangAS::Default);
> > if (HasAddrSpaceMismatch) {
> > if (llvm::Value *ptr = tryPeepholeAddrSpaceCast(Addr.getPointer(),
> > LangAS::Default, getASTAllocAddrSpace())) {
> > Addr = Address(ptr, Addr.getAlignment()); // might need to cast the
> > element type for this
> > HasAddrSpaceMismatch = false;
> > }
> > }
> It is possible RVAddrSpace is not default addr space. e.g. in OpenCL
>
> ```
> global struct S g_s;
>
> void f(struct S s);
>
> void g() {
> f(g_s);
> }
>
> ```
>
> One thing that confuses me is that why creating temp and copying can be
> skipped if RVAddrSpace equals alloca addr space. The callee is supposed to
> work on a copy of the arg, not the arg itself, right? Shouldn't the arg
> always be coped to a temp then pass to the callee?
The result of emitting an agg expression should already be a temporary. All
sorts of things would be broken if it we still had a direct reference to g_s
when we got here.
https://reviews.llvm.org/D34367
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