support Val in pow_fast, fixes #433

Author: chriselrod

src/parse/add_compute.jl

@@ -460,7 +460,12 @@ function add_compute!(
   args = @view(ex.args[2:end])
   if (instr.instr === :pow_fast || instr.instr === :(^)) && length(args) == 2
     arg2 = args[2]
-    arg2 isa Number && return add_pow!(ls, var, args[1], arg2, elementbytes, position)
+    if arg2 isa Number
+      return add_pow!(ls, var, args[1], arg2, elementbytes, position)
+    elseif arg2 isa Val
+      arg2num = Int(static(ex.args[3]))::Int
+      return add_pow!(ls, var, args[1], arg2num, elementbytes, position)
+    end
   end
   vparents = Operation[]
   deps = Symbol[]

test/miscellaneous.jl

@@ -887,7 +887,13 @@ end
     end
     x
   end
-
+function powfastmath!(x::Vector{T}) where T
+  @turbo for i = 1:length(x)
+    xv = x[i]
+    @fastmath x[i] = 1/(xv^2) 
+  end
+  x
+end
   @inline ninereturns(x) = (0.25x, 0.5x, 0.75, 1.0x, 1.25x, 1.5x, 1.75x, 2.0x, 2.25x)
   function manyreturntest(x)
     s = zero(eltype(x))
@@ -1215,7 +1221,11 @@ end
 
     @test all(isequal(81), powcseliteral!(E0))
     @test all(isequal(81), powcsesymbol!(E3))
-
+    let
+      x = rand(T,10) .+ T(0.5);
+      r = @. inv(x^2)
+      @test r ≈ powfastmath!(x)
+    end
 
     @test isapprox(
       maybe_const_issue144!(