[PATCH] D56784: [X86][SSE] Use PSLLDQ/PSRLDQ to mask out zeroable ends of a shuffle

[Roman Lebedev via Phabricator via llvm-commits]

lebedev.ri added inline comments.


================
Comment at: test/CodeGen/X86/buildvec-extract.ll:408
+; SSE-NEXT:    pslldq {{.*#+}} xmm0 = zero,zero,zero,zero,zero,zero,zero,zero,zero,zero,zero,zero,xmm0[0,1,2,3]
+; SSE-NEXT:    psrldq {{.*#+}} xmm0 = xmm0[14,15],zero,zero,zero,zero,zero,zero,zero,zero,zero,zero,zero,zero,zero,zero
+; SSE-NEXT:    retq
----------------
I'm having trouble reading this pretty-print.
Shouldn't it be something more like
```
psrldq {{.*#+}} xmm0 = zero,zero,zero,zero,zero,zero,xmm0[14,15],zero,zero,zero,zero,zero,zero,zero,zero
```
?
Otherwise to me it reads as-if it wasn't `zext i16 to 16`, but `zext i16 to i64 + shl (64-16)`
(i.e. zeros are not in MSB, but LSB)


Repository:
  rL LLVM

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