[PATCH] [X86, AVX] use blends instead of insert128 with index 0

[Sanjay Patel]

================
Comment at: test/CodeGen/X86/avx-cast.ll:9-12
@@ -6,1 +8,6 @@
 define <8 x float> @castA(<4 x float> %m) nounwind uwtable readnone ssp {
+; AVX1-LABEL: castA:
+; AVX1:         vxorps %ymm1, %ymm1, %ymm1
+; AVX1-NEXT:    vblendps {{.*#+}} ymm0 = ymm0[0,1,2,3],ymm1[4,5,6,7]
+; AVX1-NEXT:    retq
+;
----------------
andreadb wrote:
> Would it be possible to also have a test where the vector insertion is not performed on a zero vector? Apparently all the test cases you modified only seem to test the case case where a vector is inserted in the low 128-bit lane of a zero vector.
Let me make sure I understand the scenario. Is it different that this:

  define <4 x double> @shuffle_v4f64_0167(<4 x double> %a, <4 x double> %b) {
  ; ALL-LABEL: shuffle_v4f64_0167:
  ; ALL:       # BB#0:
  ; ALL-NEXT:    vblendpd {{.*#+}} ymm0 = ymm0[0,1],ymm1[2,3]
  ; ALL-NEXT:    retq
    %shuffle = shufflevector <4 x double> %a, <4 x double> %b, <4 x i32> <i32 0, i32 1, i32 6, i32 7>
    ret <4 x double> %shuffle
  }

I think the existing shuffle lowering was already detecting the non-zero version, so there are existing test cases that cover it (the above is in vector-shuffle-256-v4.ll). Please let me know if I've misunderstood.

http://reviews.llvm.org/D8366

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