[PATCH] D80285: [mlir] make the bitwidth of device side index computations configurable

Tue Jun 23 04:45:08 PDT 2020

ftynse added inline comments.

================
Comment at: mlir/include/mlir/Conversion/StandardToLLVM/ConvertStandardToLLVM.h:385
+                           /*indexBitwidth=*/kDeriveIndexBitwidthFromDataLayout,
+                           /*useAlignedAlloc=*/false},
                        PatternBenefit benefit = 1);
----------------
gysit wrote:
> ftynse wrote:
> > gysit wrote:
> > > mehdi_amini wrote:
> > > > I am puzzled how is this working?
> > > > 
> > > > This default value for this parameter is mapped to a reference member, how isn't it gonna lead to "use-after-free"?
> > > > 
> > > You are right this should not work (the lifetime of the default argument is limited to the body of the constructor -- I believe). I will submit a patch to fix this problem.
> > Hmm, why wouldn't it? The lifetime of the temporary is that of the constructor body. The reference will be used to copy-construct the member struct at the beginning of the constructor implementation, at which point the temporary is guaranteed to be live. Then we will only use the member. It would have been a problem if ConvertToLLVMPattern kept a reference to the temporary.
> >  It would have been a problem if ConvertToLLVMPattern kept a reference to the temporary.
> 
> The options member is unfortunately a const reference. 
> 
> 
My bad, I looked elsewhere. The reference capture semantics should be documented somewhere. Or in a more hacky way, this can accept a non-const reference that would effectively disallow passing in temporaries.

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  https://reviews.llvm.org/D80285/new/

https://reviews.llvm.org/D80285