refactor: don't use NaNMath.pow in codegen rewriters if integral exponent

Author: AayushSabharwal

src/code.jl

@@ -140,18 +140,14 @@ end
 
 function function_to_expr(op::typeof(^), O, st)
     args = arguments(O)
-    if length(args) == 2 && args[2] isa Real && args[2] < 0
-        ex = args[1]
-        if args[2] == -1
-            return toexpr(Term(inv, Any[ex]), st)
-        else
-            args = Any[Term(inv, Any[ex]), -args[2]]
-            op = get(st.rewrites, :nanmath, false) ? op : NaNMath.pow
-            return toexpr(Term(op, args), st)
-        end
+    if args[2] isa Real && args[2] < 0
+        args[1] = Term(inv, Any[args[1]])
+        args[2] = -args[2]
+    end
+    if get(st.rewrites, :nanmath, false) === true && !(args[2] isa Integer)
+        op = NaNMath.pow
     end
-    get(st.rewrites, :nanmath, false) === true || return nothing
-    return toexpr(Term(NaNMath.pow, args), st)
+    return toexpr(Term(op, args), st)
 end
 
 function function_to_expr(::typeof(SymbolicUtils.ifelse), O, st)

test/code.jl

@@ -100,19 +100,19 @@ nanmath_st.rewrites[:nanmath] = true
     @test toexpr(NaNMath.pow(a, b), nanmath_st) == :($(NaNMath.pow)(a, b))
 
     @test toexpr(a^2) == :($(^)(a, 2))
-    @test toexpr(a^2, nanmath_st) == :($(NaNMath.pow)(a, 2))
+    @test toexpr(a^2, nanmath_st) == :($(^)(a, 2))
     @test toexpr(NaNMath.pow(a, 2)) == :($(^)(a, 2))
-    @test toexpr(NaNMath.pow(a, 2), nanmath_st) == :($(NaNMath.pow)(a, 2))
+    @test toexpr(NaNMath.pow(a, 2), nanmath_st) == :($(^)(a, 2))
 
     @test toexpr(a^-1) == :($(/)(1, a))
     @test toexpr(a^-1, nanmath_st) == :($(/)(1, a))
     @test toexpr(NaNMath.pow(a, -1)) == :($(inv)(a))
     @test toexpr(NaNMath.pow(a, -1), nanmath_st) == :($(inv)(a))
 
     @test toexpr(a^-2) == :($(/)(1, $(^)(a, 2)))
-    @test toexpr(a^-2, nanmath_st) == :($(/)(1, $(NaNMath.pow)(a, 2)))
-    @test toexpr(NaNMath.pow(a, -2)) == :($(NaNMath.pow)($(inv)(a), 2))
-    @test toexpr(NaNMath.pow(a, -2), nanmath_st) == :($(NaNMath.pow)($(inv)(a), 2))
+    @test toexpr(a^-2, nanmath_st) == :($(/)(1, $(^)(a, 2)))
+    @test toexpr(NaNMath.pow(a, -2)) == :($(^)($(inv)(a), 2))
+    @test toexpr(NaNMath.pow(a, -2), nanmath_st) == :($(^)($(inv)(a), 2))
 
     f = GlobalRef(NaNMath, :sin)
     test_repr(toexpr(LiteralExpr(:(let x=1, y=2