fix support for -1^x, fixes #441 (#442)

Author: chriselrod

Project.toml

@@ -1,7 +1,7 @@
 name = "LoopVectorization"
 uuid = "bdcacae8-1622-11e9-2a5c-532679323890"
 authors = ["Chris Elrod <[email protected]>"]
-version = "0.12.134"
+version = "0.12.135"
 
 [deps]
 ArrayInterface = "4fba245c-0d91-5ea0-9b3e-6abc04ee57a9"
@@ -52,5 +52,5 @@ SpecialFunctions = "1, 2"
 Static = "0.7"
 ThreadingUtilities = "0.5"
 UnPack = "1"
-VectorizationBase = "0.21.21"
+VectorizationBase = "0.21.53"
 julia = "1.6"

src/parse/add_compute.jl

@@ -459,7 +459,11 @@ function add_compute!(
   instr = instruction!(ls, first(ex.args))::Instruction
   args = @view(ex.args[2:end])
   if (instr.instr === :pow_fast || instr.instr === :(^)) && length(args) == 2
+    arg1 = args[1]
     arg2 = args[2]
+    if arg1 isa Number && convert(Float64, arg1) === -1.0
+      return add_compute!(ls, var, :(2iseven($arg2)-1), elementbytes, position, mpref)
+    end
     if arg2 isa Number
       return add_pow!(ls, var, args[1], arg2, elementbytes, position)
     elseif arg2 isa Val

test/miscellaneous.jl

@@ -184,7 +184,28 @@ end
   # @test LoopVectorization.choose_order(lsvar) == (Symbol[:j,:i], :j, Symbol("##undefined##"), :j, 8, -1)
   #     @test LoopVectorization.choose_order(lsvar) == (Symbol[:j,:i], :j, :i, :j, 2, 6)
   # end
+  function piestsimd(rounds)
+    pi = 1.0
 
+    @simd for i in 2:(rounds + 2)
+      x = (-1)^iseven(i)
+      pi += x / (2 * i - 1)
+    end
+
+    return pi*4
+  end
+  function piestturbo(rounds)
+    pi = 1.0
+
+    @turbo for i in 2:(rounds + 2)
+      x = (-1)^iseven(i)
+      pi += x / (2 * i - 1)
+    end
+
+    return pi*4
+  end
+  @test piestturbo(4096) ≈ π rtol = 1e-4
+  @test piestturbo(2000) ≈ piestsimd(2000)
   function myvar!(s², A, x̄)
     @. s² = 0
     @inbounds for i ∈ 1:size(A, 2)