[PATCH] propagate IR-level fast-math-flags to DAG nodes

Thu Apr 16 19:49:37 PDT 2015

In http://reviews.llvm.org/D8900#157359, @spatel wrote:

> Let me ask a dumb question since I don't know any better. :)
>
> Is the size of an SDNode so critical that we can't do the proper software engineering thing: add the flags as a member rather than riding on the bonus bits available in SubclassData? If we do that, all of the distasteful get/set and bit shifting replication disappears.
>
> If we make a bag o' bits for the flags as in this updated patch, they'd just be single byte. As it stands, I'm showing that the sizeof(SDNode) and sizeof(SDNodeWithFlags) are both 80 bytes (building on MacOSX 10.10). Free bits!

The size is important, but if you don't increase the size on common architectures, then you should be good to go.

> That said, there's something very wrong with this patch now...I'm seeing *intermittent* failures on seemingly unrelated codegen regression tests. Can anyone spot the bug?

Have you tried running under valgrind and/or asan/msan? Does this happen in a debug build, or just an optimized build?

http://reviews.llvm.org/D8900

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