[PATCH] D18380: [CUDA] Implement -fcuda-relaxed-constexpr, and enable it by default.

Richard Smith via cfe-commits cfe-commits at lists.llvm.org
Wed Mar 23 11:35:22 PDT 2016

rsmith added inline comments.

Comment at: include/clang/Driver/CC1Options.td:702-703
@@ -701,2 +701,4 @@
   HelpText<"Allow variadic functions in CUDA device code.">;
+def fcuda_relaxed_constexpr : Flag<["-"], "fcuda-relaxed-constexpr">,
+  HelpText<"Treat constexpr functions as __host__ __device__.">;
jlebar wrote:
> rsmith wrote:
> > Is there a better name we can use for this? I don't think this is "relaxed" in any obvious sense. `-fcuda-host-device-constexpr` or `-fcuda-constexpr-on-device` might be clearer?
> "relaxed constexpr" is nvidia's term -- do you think it might be helpful to use the same terminology?  I understand there's some prior art here, with respect to clang accepting gcc's flags, although the situation here is of course different.
I think it's problematic to use that terminology, as "relaxed constexpr" is also used to describe the C++14 `constexpr` rules (see [n3652](http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2013/n3652.html)).

Comment at: lib/Driver/Tools.cpp:3597
@@ -3596,2 +3596,3 @@
+    CmdArgs.push_back("-fcuda-relaxed-constexpr");
jlebar wrote:
> rsmith wrote:
> > For flags that are enabled by default, we usually have the -cc1 flag be a `-fno-*` flag. This allows people to use (for instance) `clang blah.cu -Xclang -fno-cuda-relaxed-constexpr` if necessary.
> Yeah, Artem and I had a discussion about this yesterday.  As you can see, there are two other flags above which are turned on by default -- these also lack -fno variants.
> I think it would be good to be consistent here.  I'm tempted to add another patch below this one which makes the other two -fno, then we can make this one -fno as well.  It seems that convention is to just get rid of the existing non-fno flags, rather than leave both positive and negative versions.
> Does that sound OK to you?
Yes, that sounds fine.


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