https://bugs.llvm.org/show_bug.cgi?id=45941
Bug ID: 45941
Summary: Suboptimal optimization for vector-move operation
Product: libraries
Version: trunk
Hardware: PC
OS: Linux
Status: NEW
Severity: enhancement
Priority: P
Component: Backend: X86
Assignee: unassignedb...@nondot.org
Reporter: d...@dsprenkels.com
CC: craig.top...@gmail.com, llvm-bugs@lists.llvm.org,
llvm-...@redking.me.uk, spatel+l...@rotateright.com
https://godbolt.org/z/a3mRRf
---
On X86, the shuffle operation
ymm: [x0: i32, x1: i32, x2: i32, x3: i32, ...]
=>
ymm: [x0: i64, x1: i64, x2: i64, x3: i64]
can be implemented efficiently using a `vpmovzxdq` instruction.
LLVM uses a normal `vpshufb` instruction, which needs to load the list of
indices. Using a `vpmovzxdq` instruction would erase this load.
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