[PATCH] D37236: [InstCombine] add insertelement + shuffle demanded element fold

[Craig Topper via Phabricator via llvm-commits]

craig.topper added a comment.

I agree there are definitely cases where your change is required. I was just confused how we got a multiple use that didn't exist in the  original IR.

My fix seems to be needed to get rid of %out012 in this test case

  define <4 x i32> @add_ps_002(<4 x i32> %a, <4 x i32> %b) {
    %a0 = extractelement <4 x i32> %a, i32 0
    %a1 = extractelement <4 x i32> %a, i32 1
    %a2 = extractelement <4 x i32> %a, i32 2
    %a3 = extractelement <4 x i32> %a, i32 3
    %a0_again = extractelement <4 x i32> %a, i32 0
    %a1_again = extractelement <4 x i32> %a, i32 1
    %a2_again = extractelement <4 x i32> %a, i32 2
    %a3_again = extractelement <4 x i32> %a, i32 3
    %add01 = add i32 %a0, %a1
    %add23 = add i32 %a2, %a3
    %add01_again = add i32 %a0_again, %a1_again
    %add23_again = add i32 %a2_again, %a3_again
    %out0 = insertelement <4 x i32> undef, i32 %add01, i32 0
    %out01 = insertelement <4 x i32> %out0, i32 %add23, i32 1
    %out012 = insertelement <4 x i32> %out01, i32 %add01_again, i32 2
    %foo = add <4 x i32> %out012, %b
    %out0123 = insertelement <4 x i32> %foo, i32 %add23_again, i32 3
    %shuffle = shufflevector <4 x i32> %out0123, <4 x i32> %a, <4 x i32> <i32 0, i32 1, i32 undef, i32 undef>
    ret <4 x i32> %shuffle
  }


https://reviews.llvm.org/D37236