consider fncall param aligns when calculating access size #596
Conversation
|
No regression found from LLVM unit tests |
| if (!arg.first->getType().isPtrType()) | ||
| continue; | ||
|
|
||
| if (arg.second.has(ParamAttrs::Dereferenceable)) { |
There was a problem hiding this comment.
what if the function takes 2 pointers, one with dereferenceable/align and one without? Then min access needs to be 1, right?
There was a problem hiding this comment.
I think in the case min access can be larger than 1, but due to a non-trivial reason.
I'll describe why I think so.
call f(dereferenceable(4) align 4 %p, %q) is equivalent to a dummy load followed by the call:
load i32 %p, align 4 // a dummy load
call f(%p, %q)
The dummy load contributes to the min access size, as a real load instruction does.
However, for the call f(%p, %q), I think it shouldn't set the min access size to 1; otherwise it deoptimizes too many things.
I think we can assume that a call updates the memory with min access size granularity.
Assuming that this dummy load idea makes sense, I think pointer arguments without dereferenceable shouldn't update the min access size.
… in case this is a valid claim)
This PR resolves #480 .