Commits on Nov 6, 2024

1. [CostModel][AArch64] Make extractelement, with fmul user, free whenev… …

   …er possible
   
   In case of Neon, if there exists extractelement from lane != 0 such that
     1. extractelement does not necessitate a move from vector_reg -> GPR.
     2. extractelement result feeds into fmul.
     3. Other operand of fmul is a scalar or extractelement from lane 0 or lane equivalent to 0.
     then the extractelement can be merged with fmul in the backend and it incurs no cost.
     e.g.
     define double @foo(<2 x double> %a) {
       %1 = extractelement <2 x double> %a, i32 0
       %2 = extractelement <2 x double> %a, i32 1
       %res = fmul double %1, %2    ret double %res
     }
     %2 and %res can be merged in the backend to generate:
     fmul    d0, d0, v0.d[1]
   
   The change was tested with SPEC FP(C/C++) on Neoverse-v2.
   Compile time impact: None
   Performance impact: Observing 1.3-1.7% uplift on lbm benchmark with -flto depending upon the config.

   

   sushgokh committed Nov 6, 2024
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