[PATCH] D133300: [InstCombine] Matrix multiplication negation optimisation

[Sanjay Patel via Phabricator via llvm-commits]

spatel added a comment.

In D133300#3781177 <https://reviews.llvm.org/D133300#3781177>, @zjaffal wrote:

> - In the cases where both operands are negated we may need to introduce a seperate patch to handle that case

Yes, and it should be written first. Without it, we have inconsistent behavior. This patch will reduce the 2nd example below, but it misses the 1st even though they are very similar patterns:

  define <9 x double> @test_with_two_operands_negated2_commute(<3 x double> %a, <27 x double> %b){
    %a.neg = fneg <3 x double> %a
    %b.neg = fneg <27 x double> %b
    %res = call <9 x double> @llvm.matrix.multiply.v9f64.v3f64.v27f64(<3 x double> %a.neg, <27 x double> %b.neg, i32 1, i32 3, i32 9)
    ret <9 x double> %res
  }
  
  define <9 x double> @test_with_two_operands_negated2(<27 x double> %a, <3 x double> %b){
    %a.neg = fneg <27 x double> %a
    %b.neg = fneg <3 x double> %b
    %res = tail call <9 x double> @llvm.matrix.multiply.v9f64.v27f64.v3f64(<27 x double> %a.neg, <3 x double> %b.neg, i32 9, i32 3, i32 1)
    ret <9 x double> %res
  }


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