fix at-ccall (#434)

Author: pfitzseb

src/optimize.jl

@@ -270,13 +270,25 @@ function build_compiled_call!(stmt::Expr, fcall, code, idx, nargs::Int, sparams:
             if atype === Any
                 push!(args, arg)
             else
-                @assert arg isa SSAValue
-                unsafe_convert_expr = code.code[arg.id]::Expr
-                push!(delete_idx, arg.id) # delete the unsafe_convert
-                cconvert_stmt = unsafe_convert_expr.args[3]::SSAValue
-                push!(delete_idx, cconvert_stmt.id) # delete the cconvert
-                cconvert_expr = code.code[cconvert_stmt.id]::Expr
-                push!(args, cconvert_expr.args[3])
+                if arg isa SSAValue
+                    unsafe_convert_expr = code.code[arg.id]::Expr
+                    push!(delete_idx, arg.id) # delete the unsafe_convert
+                    cconvert_stmt = unsafe_convert_expr.args[3]::SSAValue
+                    push!(delete_idx, cconvert_stmt.id) # delete the cconvert
+                    cconvert_expr = code.code[cconvert_stmt.id]::Expr
+                    push!(args, cconvert_expr.args[3])
+                elseif arg isa SlotNumber
+                    index = findfirst(code.code) do expr
+                        expr isa Expr || return false
+                        lhs = expr.args[1]
+                        return lhs isa SlotNumber && lhs.id === arg.id
+                    end
+                    unsafe_convert_expr = code.code[index]::Expr
+                    push!(delete_idx, index) # delete the unsafe_convert
+                    push!(args, unsafe_convert_expr.args[2])
+                else
+                    error("unexpected foreigncall argument type encountered: $(typeof(arg))")
+                end
             end
         end
     else

test/interpret.jl

@@ -702,3 +702,10 @@ end
     frame = JuliaInterpreter.enter_call(A396, 3)
     @test length(JuliaInterpreter.locals(frame)) > 0
 end
+
+@static if VERSION >= v"1.5" && Sys.islinux()
+    @testset "@ccall" begin
+        f(s) = @ccall strlen(s::Cstring)::Csize_t
+        @test @interpret(f("asd")) == 3
+    end
+end