rnk added inline comments.
================
Comment at: clang/lib/CodeGen/CGExpr.cpp:103
+ if (!ArraySize) {
+ auto *EBB = AllocaInsertPt->getParent();
+ auto Iter = AllocaInsertPt->getIterator();
----------------
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.
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D110257/new/
https://reviews.llvm.org/D110257
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