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

[Alexey Bataev via Phabricator via cfe-commits]

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:
> > 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.


Repository:
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  https://reviews.llvm.org/D71475/new/

https://reviews.llvm.org/D71475