hsmhsm added inline comments.
================
Comment at: clang/lib/CodeGen/CGExpr.cpp:103
+ if (!ArraySize) {
+ auto *EBB = AllocaInsertPt->getParent();
+ auto Iter = AllocaInsertPt->getIterator();
----------------
rnk wrote:
> hsmhsm wrote:
> > jdoerfert wrote:
> > > arsenm wrote:
> > > > Why is there a special AllocaInsertPt iterator in the first place? Can
> > > > you avoid any iteration logic by just always inserting at the block
> > > > start?
> > > Right. The alloca insertion point is sometimes changed to a non-entry
> > > block, and we should keep that ability.
> > > From all the use cases I know it would suffice to insert at the beginning
> > > of the alloca insertion point block though.
> > I really do not understand this comment fully.
> >
> > This block of code here inserts an "addressspace cast" of recently inserted
> > alloca, not the alloca itself. Alloca is already inserted. Please look at
> > the start of this function.
> >
> > The old logic (in the left) inserts addressspace cast of recently inserted
> > alloca immediately after recent alloca using AllocaInsertPt. As a side
> > effect, it also makes AllocaInsertPt now point to this newly inserted
> > addressspace cast. Hence, next alloca is inserted after this new
> > addressspace cast, because now AllocaInsertPt is made to point this newly
> > inserted addressspace cast.
> >
> > The new logic (here) fixes that by moving insertion point just beyond
> > current AllocaInsertPt without updating AllocaInsertPt.
> >
> > How can I insert "addressspace cast" of an alloca, at the beginning of the
> > block even before alloca?
> >
> > As I understand it, AllocaInsertPt is maintained to insert static allocas
> > at the start of entry block, otherwise there is no any special reason to
> > maintain such a special insertion point. Please look at
> > https://github.com/llvm/llvm-project/blob/main/clang/lib/CodeGen/CodeGenFunction.h#L378.
> >
> > That said, I am not really sure, if I have completely misunderstood the
> > comment above. If that is the case, then, I need better clarification here
> > about what really is expected.
> Well, inserting at the top of the entry block would reverse the order of the
> allocas. Currently they appear in source/IRGen order, which is nice.
> Maintaining the order requires appending, which requires a cursor of some
> kind.
Yes, correct.
And I am waiting for further inputs from @yaxunl / @arsenm / @jdoerfert
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D110257/new/
https://reviews.llvm.org/D110257
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