ccall: support different types for vararg arguments (#32800)

Not currently supported in the front-end syntax, this modifies the backend to represent it
and be capable of handling it (and need fewer lines of code!).

Author: vtjnash

base/compiler/ssair/passes.jl

@@ -575,7 +575,7 @@ function getfield_elim_pass!(ir::IRCode, domtree::DomTree)
             is_getfield = true
             is_unchecked = true
         elseif isexpr(stmt, :foreigncall)
-            nccallargs = stmt.args[5]
+            nccallargs = length(stmt.args[3]::SimpleVector)
             new_preserves = Any[]
             old_preserves = stmt.args[(6+nccallargs):end]
             for (pidx, preserved_arg) in enumerate(old_preserves)
@@ -817,7 +817,7 @@ function getfield_elim_pass!(ir::IRCode, domtree::DomTree)
         # Insert the new preserves
         for (use, new_preserves) in preserve_uses
             useexpr = ir[SSAValue(use)]
-            nccallargs = useexpr.args[5]
+            nccallargs = length(useexpr.args[3]::SimpleVector)
             old_preserves = filter(ssa->!isa(ssa, SSAValue) || !(ssa.id in intermediaries), useexpr.args[(6+nccallargs):end])
             new_expr = Expr(:foreigncall, useexpr.args[1:(6+nccallargs-1)]...,
                 old_preserves..., new_preserves...)

base/compiler/validation.jl

@@ -23,7 +23,7 @@ const VALID_EXPR_HEADS = IdDict{Any,Any}(
     :copyast => 1:1,
     :meta => 0:typemax(Int),
     :global => 1:1,
-    :foreigncall => 3:typemax(Int),
+    :foreigncall => 5:typemax(Int), # name, RT, AT, nreq, cconv, args..., roots...
     :cfunction => 5:5,
     :isdefined => 1:1,
     :loopinfo => 0:typemax(Int),

base/meta.jl

@@ -313,9 +313,9 @@ function _partially_inline!(@nospecialize(x), slot_replacements::Vector{Any},
                 elseif i == 3
                     x.args[3] = Core.svec(Any[_instantiate_type_in_env(argt, type_signature, static_param_values) for argt in x.args[3]]...)
                 elseif i == 4
-                    @assert isa((x.args[4]::QuoteNode).value, Symbol)
+                    @assert isa(x.args[4], Int)
                 elseif i == 5
-                    @assert isa(x.args[5], Int)
+                    @assert isa((x.args[5]::QuoteNode).value, Symbol)
                 else
                     x.args[i] = _partially_inline!(x.args[i], slot_replacements,
                                                    type_signature, static_param_values,

doc/src/devdocs/ast.md

@@ -469,6 +469,39 @@ These symbols appear in the `head` field of [`Expr`](@ref)s in lowered form.
 
       * `:inline` and `:noinline`: Inlining hints.
 
+  * `foreigncall`
+
+    Statically-computed container for `ccall` information. The fields are:
+
+      * `args[1]` : name
+
+        The expression that'll be parsed for the foreign function.
+
+      * `args[2]::Type` : RT
+
+        The (literal) return type, computed statically when the containing method was defined.
+
+      * `args[3]::SimpleVector` (of Types) : AT
+
+        The (literal) vector of argument types, computed statically when the containing method was defined.
+
+      * `args[4]::Int` : nreq
+
+        The number of required arguments for a varargs function definition.
+
+      * `args[5]::QuoteNode{Symbol}` : calling convention
+
+        The calling convention for the call.
+
+      * `args[6:length(args[3])]` : arguments
+
+        The values for all the arguments (with types of each given in args[3]).
+
+      * `args[(length(args[3]) + 1):end]` : gc-roots
+
+        The additional objects that may need to be gc-rooted for the duration of the call.
+        See [Working with LLVM](@ref Working-with-LLVM) for where these are derived from and how they get handled.
+
 
 ### Method
 

doc/src/devdocs/llvm.md

@@ -277,7 +277,7 @@ need to make sure that the array does stay alive while we're doing the
 [`ccall`](@ref). To understand how this is done, first recall the lowering of the
 above code:
 ```julia
-return $(Expr(:foreigncall, :(:foo), Cvoid, svec(Ptr{Float64}), :(:ccall), 1, :($(Expr(:foreigncall, :(:jl_array_ptr), Ptr{Float64}, svec(Any), :(:ccall), 1, :(A)))), :(A)))
+return $(Expr(:foreigncall, :(:foo), Cvoid, svec(Ptr{Float64}), 0, :(:ccall), Expr(:foreigncall, :(:jl_array_ptr), Ptr{Float64}, svec(Any), 0, :(:ccall), :(A)), :(A)))
 ```
 The last `:(A)`, is an extra argument list inserted during lowering that informs
 the code generator which Julia level values need to be kept alive for the