[PATCH] D106280: [X86][AVX] scalar_to_vector(load_scalar()) -> load_vector() for fast dereferencable loads

[Pengfei Wang via Phabricator via llvm-commits]

pengfei added inline comments.


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Comment at: llvm/test/CodeGen/X86/load-partial-dot-product.ll:183
 ; AVX-NEXT:    vinsertps {{.*#+}} xmm0 = xmm0[0,1],mem[0],xmm0[3]
-; AVX-NEXT:    vmovsd {{.*#+}} xmm1 = mem[0],zero
+; AVX-NEXT:    vmovups (%rsi), %xmm1
 ; AVX-NEXT:    vinsertps {{.*#+}} xmm1 = xmm1[0,1],mem[0],xmm1[3]
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RKSimon wrote:
> efriedma wrote:
> > Even if we're allowed to do this, it doesn't seem wise; having zero in the high bits of the register is better than random junk.  Can we mark up the loads somehow?
> Isn't that what the dereferenceable(16) tag is doing?
I have the same doubt. `dereferenceable(16)` tells the memory of the high bits is available. But shouldn't we always prefer to loading less bytes for performance?


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