[PATCH] D38756: [x86] use an insert op to put one variable element into a constant of vectors

[Eli Friedman via Phabricator via llvm-commits]

efriedma added a comment.

> This doesn't happen with int constants...because int constants are legal but FP constants are not?

Yes, exactly.

We call LowerBUILD_VECTOR before we legalize the operands of a BUILD_VECTOR, so that shouldn't block this optimization.  But we don't recompute the topological ordering when you create new nodes, so legalization can happen in an unexpected order if you create illegal nodes (by, for example, calling getBuildVector()).


https://reviews.llvm.org/D38756