implement @trace for (#255)

* implement `@trace` for

* Apply suggestions from code review

Co-authored-by: Sergio Sánchez Ramírez <15837247+mofeing@users.noreply.github.com>

* Allow using induction variable

* floating point ranges

* lightspeed

* import LinearAlgebra

* generate 0 to N loop

* ir test

* clean iter

* Revert "Apply suggestions from code review"

This reverts commit 079ed4a.

* remove precompilation warning

* format and fix

* loop ranges as traced numbers

* fmt and add non unit step test

* fmt2

* integers

---------

Co-authored-by: Sergio Sánchez Ramírez <15837247+mofeing@users.noreply.github.com>

lib/ReactantCore/src/ReactantCore.jl

@@ -31,6 +31,7 @@ if no traced value is found inside the expression, then there is no overhead.
 - `if` conditions (with `elseif` and other niceties) (`@trace if ...`)
 - `if` statements with a preceeding assignment (`@trace a = if ...`) (note the positioning
   of the macro needs to be before the assignment and not before the `if`)
+- `for` statements with a single induction variable iterating over a syntactic `StepRange` of integers.
 
 ## Special Considerations
 
@@ -81,6 +82,15 @@ end
 This will not compile since `y` is a `Float32` in one branch and a `Float64` in the other.
 You need to ensure that all branches have the same type.
 
+Another example is the following for loop which changes the type of `x` between iterations.
+
+```julia
+x = ... # ConcreteRArray{Int64, 1}
+for i in 1f0:0.5f0:10f0
+    x = x .+ i # ConcreteRArray{Float32, 1}
+end
+```
+
 ### Certain Symbols are Reserved
 
 Symbols like $(SPECIAL_SYMBOLS) are not allowed as variables in `@trace` expressions. While certain cases might work but these are not guaranteed to work. For
@@ -100,15 +110,84 @@ end
 """
 macro trace(expr)
     expr = macroexpand(__module__, expr)
-    if expr.head == :(=)
-        if expr.args[2] isa Expr && expr.args[2].head == :if
+    if Meta.isexpr(expr, :(=))
+        if Meta.isexpr(expr.args[2], :if)
             return esc(trace_if_with_returns(__module__, expr))
         end
     end
-    expr.head == :if && return esc(trace_if(__module__, expr))
+    Meta.isexpr(expr, :if) && return esc(trace_if(__module__, expr))
+    Meta.isexpr(expr, :for) && return (esc(trace_for(__module__, expr)))
     return error("Only `if-elseif-else` blocks are currently supported by `@trace`")
 end
 
+function trace_for(mod, expr)
+    Meta.isexpr(expr, :for, 2) || error("expected for expr")
+    assign, body = expr.args
+
+    error_if_any_control_flow(body)
+    if !Meta.isexpr(assign, :(=)) ||
+        !(assign.args[1] isa Symbol) ||
+        !Meta.isexpr(assign.args[2], :call) ||
+        assign.args[2].args[1] !== :(:)
+        error("malformed for loop assignment")
+    end
+
+    induction, range = assign.args
+
+    counter = gensym(:i)
+    num_iters = gensym(:num_iters)
+
+    start = range.args[2]
+    step = length(range.args) == 3 ? 1 : range.args[3]
+    limit = range.args[end]
+
+    body_symbols = ExpressionExplorer.compute_symbols_state(
+        quote
+            $(Expr(:local, assign))
+            $body
+        end,
+    )
+
+    external_syms = body_symbols.assignments ∪ body_symbols.references
+    filter!(∉(SPECIAL_SYMBOLS), external_syms)
+
+    all_syms = Expr(:tuple, counter, external_syms...)
+    args_init = Expr(
+        :tuple, :(Reactant.promote_to(Reactant.TracedRNumber{Int}, 0)), external_syms...
+    )
+
+    reactant_code_block = quote
+        let args = $(args_init)
+            cond_fn =
+                $(all_syms) -> begin
+                    local num_iters = div($limit - $start, $step, RoundDown)
+                    local num_iters = Reactant.promote_to(
+                        Reactant.TracedRNumber{Int64}, num_iters
+                    )
+                    $counter < num_iters + 1
+                end
+            body_fn =
+                $(all_syms) -> begin
+                    local step_ = $step
+                    local start_ = $start
+                    local $induction = start_ + $counter * step_
+                    $body
+                    ($counter + 1, $(all_syms.args[(begin + 1):end]...))
+                end
+
+            $(ReactantCore).traced_while(cond_fn, body_fn, args)
+        end
+    end
+
+    return quote
+        if any($(is_traced), $(Expr(:tuple, all_syms.args[(begin + 1):end]...)))
+            $(reactant_code_block)
+        else
+            $(expr)
+        end
+    end
+end
+
 # ... = if ... style expressions
 function trace_if_with_returns(mod, expr)
     new_expr, _, all_check_vars = trace_if(
@@ -128,7 +207,7 @@ function trace_if(mod, expr; store_last_line=nothing, depth=0)
     original_expr = expr
 
     if depth == 0
-        error_if_return(expr)
+        error_if_any_control_flow(expr)
 
         counter = 0
         expr = MacroTools.prewalk(expr) do x
@@ -285,6 +364,13 @@ function traced_if(cond, true_fn::TFn, false_fn::FFn, args) where {TFn,FFn}
     return cond ? true_fn(args) : false_fn(args)
 end
 
+function traced_while(cond_fn, body_fn, args) where {CFn,BFn}
+    while cond_fn(args...)
+        args = body_fn(args...)
+    end
+    return args
+end
+
 function cleanup_expr_to_avoid_boxing(expr, prepend::Symbol, all_vars)
     return MacroTools.postwalk(expr) do x
         if x isa Symbol && x ∈ all_vars
@@ -294,10 +380,14 @@ function cleanup_expr_to_avoid_boxing(expr, prepend::Symbol, all_vars)
     end
 end
 
-function error_if_return(expr)
+const CONTROL_FLOW_EXPRS = [:return, :break, :continue, :symbolicgoto]
+
+function error_if_any_control_flow(expr)
     return MacroTools.postwalk(expr) do x
-        if x isa Expr && x.head == :return
-            error("Cannot use @trace on a block that contains a return statement")
+        for head in CONTROL_FLOW_EXPRS
+            if Meta.isexpr(x, head)
+                error("Cannot use @trace on a block that contains a $head statement")
+            end
         end
         return x
     end

src/Compiler.jl

@@ -417,15 +417,15 @@ macro code_hlo(options, maybe_call=nothing)
             f = $(fname)
             args = $(Expr(:vect, call.args[2:end]...))
             mode = first($(compile_mlir)(f, args; optimize=options.optimize))
-            return mode
+            mode
         end
     elseif Meta.isexpr(call, :(.), 2) && Meta.isexpr(call.args[2], :tuple)
         quote
             options = $(options)
             f = Base.Broadcast.BroadcastFunction($(call.args[1]))
             args = $(call.args[2:end]...)
             mode = first($(compile_mlir)(f, args; optimize=options.optimize))
-            return mode
+            mode
         end
     else
         error("Invalid function call: $(call)")

src/ControlFlow.jl

@@ -74,9 +74,70 @@ function ReactantCore.traced_if(
     end
 end
 
-function get_region_removing_missing_values(compiled_fn, insertions)
+function ReactantCore.traced_while(
+    cond_fn::CFn, body_fn::BFn, args
+) where {CFn<:Function,BFn<:Function}
+    # TODO: detect and prevent mutation within the condition
+
+    # We promote all incoming args (is there a better way to do this?)
+    traced_args = [
+        if v isa Number && !(v isa TracedType)
+            Reactant.promote_to(TracedRNumber{typeof(v)}, v)
+        else
+            v
+        end for v in args
+    ]
+
+    (_, cond_fn_compiled, cond_fn_results, _, _, _, _, in_tys, cond_fn_linear_results) = Reactant.make_mlir_fn(
+        cond_fn,
+        traced_args,
+        (),
+        string(gensym("cond_fn")),
+        false;
+        no_args_in_result=true,
+        return_dialect=:stablehlo,
+        do_transpose=false,
+    )
+
+    (_, body_fn_compiled, body_fn_results, _, _, _, _, _, body_fn_linear_results) = Reactant.make_mlir_fn(
+        body_fn,
+        traced_args,
+        (),
+        string(gensym("body_fn")),
+        false;
+        no_args_in_result=true,
+        return_dialect=:stablehlo,
+        do_transpose=false,
+    )
+
+    cond_reg = take_region(cond_fn_compiled)
+    body_reg = take_region(body_fn_compiled)
+
+    MLIR.IR.rmfromparent!(cond_fn_compiled)
+    MLIR.IR.rmfromparent!(body_fn_compiled)
+
+    result_0 = in_tys
+
+    operands = MLIR.IR.Value[v.mlir_data for v in traced_args]
+
+    while_compiled = MLIR.Dialects.stablehlo.while_(
+        operands; result_0, cond=cond_reg, body=body_reg
+    )
+
+    return map(enumerate(traced_args)) do (i, res)
+        res.mlir_data = MLIR.IR.result(while_compiled, i)
+        return res
+    end
+end
+
+function take_region(compiled_fn)
     region = MLIR.IR.Region()
     MLIR.API.mlirRegionTakeBody(region, MLIR.API.mlirOperationGetRegion(compiled_fn, 0))
+    return region
+end
+
+function get_region_removing_missing_values(compiled_fn, insertions)
+    region = take_region(compiled_fn)
     block = MLIR.IR.Block(MLIR.API.mlirRegionGetFirstBlock(region), false)
     return_op = MLIR.IR.terminator(block)
     for (i, rt) in insertions

src/TracedRNumber.jl

@@ -124,6 +124,20 @@ for (jlop, hloop) in (
     end
 end
 
+function Base.div(
+    @nospecialize(lhs::TracedRNumber{T}), rhs, ::typeof(RoundDown)
+) where {T<:Integer}
+    return TracedRNumber{T}(
+        (),
+        MLIR.IR.result(
+            MLIR.Dialects.stablehlo.divide(
+                lhs.mlir_data, promote_to(TracedRNumber{T}, rhs).mlir_data
+            ),
+            1,
+        ),
+    )
+end
+
 for (jlop, hloop, hlocomp) in (
     (:(Base.:(==)), :compare, "EQ"),
     (:(Base.:(!=)), :compare, "NE"),

src/utils.jl

@@ -43,6 +43,7 @@ function make_mlir_fn(
     return_dialect=:func,
     no_args_in_result::Bool=false,
     construct_function_without_args::Bool=false,
+    do_transpose=true,
 )
     if sizeof(typeof(f)) != 0 || f isa BroadcastFunction
         return (
@@ -57,6 +58,7 @@ function make_mlir_fn(
                 return_dialect,
                 no_args_in_result,
                 construct_function_without_args,
+                do_transpose,
             )[2:end]...,
         )
     end
@@ -82,8 +84,10 @@ function make_mlir_fn(
 
     in_tys = if toscalar
         [MLIR.IR.TensorType((), MLIR.IR.Type(eltype(arg))) for arg in linear_args]
-    else
+    elseif do_transpose
         [transpose_ty(mlir_type(arg)) for arg in linear_args]
+    else
+        [mlir_type(arg) for arg in linear_args]
     end
 
     sym_visibility = nothing
@@ -115,7 +119,7 @@ function make_mlir_fn(
                 arg.mlir_data = args[i].mlir_data
             else
                 raw_arg = MLIR.IR.argument(fnbody, i)
-                row_maj_arg = transpose_val(raw_arg)
+                row_maj_arg = do_transpose ? transpose_val(raw_arg) : raw_arg
                 arg.mlir_data = row_maj_arg
             end
         end
@@ -180,12 +184,12 @@ function make_mlir_fn(
     ret = MLIR.IR.block!(fnbody) do
         vals = MLIR.IR.Value[]
         for res in linear_results
-            if res isa MissingTracedValue
-                col_maj = broadcast_to_size(false, ()).mlir_data
-            elseif construct_function_without_args
-                col_maj = res.mlir_data
-            else
-                col_maj = transpose_val(res.mlir_data)
+            col_maj = if res isa MissingTracedValue
+                broadcast_to_size(false, ()).mlir_data
+            elseif construct_function_without_args || !do_transpose
+                res.mlir_data
+            elseif do_transpose
+                transpose_val(res.mlir_data)
             end
             push!(vals, col_maj)
         end