https://bugs.llvm.org/show_bug.cgi?id=52013
Bug ID: 52013
Summary: Spurious shuffle shows up in generated code
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/dPa48Gez1 this is a reduced test case based on this
xnnpack source file
https://github.com/google/XNNPACK/blob/0bf8afaa43601ab37407f262c90ec3c02436a600/src/f32-spmm/gen/32x1-minmax-wasmsimd-x86.c
What's interesting is that i8x16.shuffle shows up twice in the generated code,
but there is no explicit use of shuffle in the source.
Looking at the second i8x16.shuffle, on line 52 of the generated code:
30 v128.load32_splat 0:p2align=0
31 local.set 10
...
51 local.get 10
52 i8x16.shuffle 0, 1, 2, 3, 0, 1, 2, 3, 0, 1, 2, 3, 0, 1, 2, 3
it tries to shuffle the result of a v128.load32_splat. Which isn't needed:
- the shuffle is a 32x4 splat
- we already did a splat in the v128.load32_splat
- the shuffle is actually a nop
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