inline native Julia scalars encountered in f.(args...) AST

src/ast.c

@@ -191,11 +191,29 @@ value_t fl_invoke_julia_macro(fl_context_t *fl_ctx, value_t *args, uint32_t narg
     return scmresult;
 }
 
+// Check whether v is a scalar for purposes of inlining fused-broadcast
+// arguments when lowering; should agree with broadcast.jl on what is a
+// scalar.  When in doubt, return false, since this is only an optimization.
+// (TODO: update after #16966 is resolved.)
+int fl_julia_scalar(fl_context_t *fl_ctx, value_t *args, uint32_t nargs)
+{
+    argcount(fl_ctx, "julia-scalar?", nargs, 1);
+    if (fl_isnumber(fl_ctx, args[0]))
+        return fl_ctx->T;
+    else if (iscvalue(args[0]) && fl_ctx->jl_sym == cv_type((cvalue_t*)ptr(args[0]))) {
+        jl_value_t *v = *(jl_value_t**)cptr(args[0]);
+        if (jl_subtype(v,(jl_value_t*)jl_number_type,1))
+            return fl_ctx->T;
+    }
+    return fl_ctx->F;
+}
+
 static const builtinspec_t julia_flisp_ast_ext[] = {
     { "defined-julia-global", fl_defined_julia_global },
     { "invoke-julia-macro", fl_invoke_julia_macro },
     { "current-julia-module", fl_current_julia_module },
     { "current-julia-module-counter", fl_current_module_counter },
+    { "julia-scalar?", fl_julia_scalar },
     { NULL, NULL }
 };
 

src/julia-syntax.scm

@@ -1679,7 +1679,7 @@
                                 new-fargs new-args (cons (cons (cadr farg) (cadr varfarg)) renames)
                                 varfarg vararg)
                             (error "multiple splatted args cannot be fused into a single broadcast"))))
-                   ((number? arg) ; inline numeric literals
+                   ((julia-scalar? arg) ; inline numeric literals etc.
                     (cf (cdr old-fargs) (cdr old-args)
                         new-fargs new-args
                         (cons (cons farg arg) renames)

test/broadcast.jl

@@ -289,6 +289,13 @@ let identity = error, x = [1,2,3]
     @test x == [1,1,1]
 end
 
+# make sure scalars are inlined, which causes f.(x,scalar) to lower to a "thunk"
+import Base.Meta: isexpr
+@test isexpr(expand(:(f.(x,y))), :call)
+@test isexpr(expand(:(f.(x,1))), :thunk)
+@test isexpr(expand(:(f.(x,1.0))), :thunk)
+@test isexpr(expand(:(f.(x,$π))), :thunk)
+
 # PR 16988
 @test Base.promote_op(+, Bool) === Int
 @test isa(broadcast(+, [true]), Array{Int,1})