[PATCH] D71897: [X86] Adding fp128 support for strict fcmp

[Craig Topper via Phabricator via llvm-commits]

craig.topper added a comment.

There are libcalls for OGT/OLT/OLE/OGE that are always signalling. There is a libcall for OEQ/UNE that not signalling. And there's a libcall for Ordered/Unordered that is not signalling.

Note, that despite having multiple names there are really only 3 total libcalls. The names are aliases and the return value is used to check direction. The OGT/OLT/OLE/OGE libcall returns -1, 0, or 1. The other oeq/une and the ordered/unordered just return true or false.

We may need to expand the unsupported calls into multiple compares and control flow in IR. For example for non-signalling ogt/olt/ole/oge we'll need to check unordered first and branch accordingly for qnans without calling the signalling ogt/olt/ole/oge libcall which will signal. Technically we could use a select to change the value we pass to the ogt/olt/ole/oge when its signalling, but select has to be expanded into control flow on many targets anyway. @uweigand, what are you thoughts on this?


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https://reviews.llvm.org/D71897