[PATCH] D71475: [WIP][OPENMP] Try to fix linear clause crash by emitting alloca for step

Tue Dec 17 09:14:44 PST 2019

ABataev added inline comments.

================
Comment at: clang/lib/Sema/SemaOpenMP.cpp:1128
+           (A == OMPC_firstprivate && (Data.Attributes == OMPC_lastprivate ||
+                                       Data.Attributes == OMPC_linear)) ||
            (A == OMPC_lastprivate && Data.Attributes == OMPC_firstprivate) ||
----------------
jdoerfert wrote:
> ABataev wrote:
> > jdoerfert wrote:
> > > ABataev wrote:
> > > > cchen wrote:
> > > > > ABataev wrote:
> > > > > > What is this change for?
> > > > > Since now the variable in step expression has been set as implicit firstprivate.
> > > > No need to do this, the whole expression must be evaluated before entering the parallel region.
> > > The standard is not clear on this, e.g., what if the expression has a side-effect and the loop has 0 iterations. However, evaluating it once in the beginning seems fine to me, assuming we do not evaluate it later again.
> > The standard says: `The linear-step expression must be invariant during the execution of the region that corresponds to the construct.` So, it is ok to evaluate it at the entrance to the region. The only thing that (maybe) required is to check that the expression is really invariant in the analysis phase.
> I'll just repeat the under-specified case you seem to have missed while reading my comment:
> 
> > What if the expression has a side-effect and the loop has 0 iterations.
> 
> 
> 
> 
Yes, this is not specified

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D71475/new/

https://reviews.llvm.org/D71475