https://bugs.llvm.org/show_bug.cgi?id=50436
Bug ID: 50436
Summary: Codegen for shuffle (similar to vget_low_s8) can be
improved
Product: libraries
Version: trunk
Hardware: PC
OS: All
Status: NEW
Severity: enhancement
Priority: P
Component: Backend: WebAssembly
Assignee: tliv...@google.com
Reporter: z...@google.com
CC: llvm-bugs@lists.llvm.org
PTAL https://godbolt.org/z/bhh56TxYe
The use of __builtin_shufflevector is to extract the 8 low uint8_t elements
from a uint8x16_t into a uint8x8_t. It seems like due to the way the vector
extension is used to represent Wasm's SIMD128, we are lowering to a lot of
i8x16.extract_lane and i16x8.replace_lane.
Contrast it with native x86 codegen, which is a no-op (and it is, because it is
extracting the low 64-bits of a 128-bit vector into the low 64-bits).
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