[Bug target/63351] Optimization: contract broadcast intrinsics when AVX512 is enabled

[hjl.tools at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63351
Bug 63351 depends on bug 72782, which changed state.

Bug 72782 Summary: AVX512: No support for scalar broadcasts
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=72782

           What    |Removed                     |Added
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             Status|WAITING                     |RESOLVED
         Resolution|---                         |FIXED