Ensure variable IDs and slots numbers are deterministic

Remove the dependence on Dict iteration for var_id and slot number
generation by sorting by VarKey when generating VarId, and VarId when
generating slots. This ensures that integer identifiers in the IR are
always deterministic.

src/linear_ir.jl

@@ -502,7 +502,7 @@ function compile_lambda(outer_ctx, ex)
     compile_body(ctx, ex[1])
     slot_rewrites = Dict{VarId,Int}()
     _add_slots!(slot_rewrites, ctx.var_info, (arg.var_id for arg in lambda_info.args))
-    _add_slots!(slot_rewrites, ctx.var_info, ex.lambda_locals)
+    _add_slots!(slot_rewrites, ctx.var_info, sort(collect(ex.lambda_locals)))
     code = renumber_body(ctx, ctx.code, slot_rewrites)
     makenode(ctx, ex, K"lambda",
              makenode(ctx, ex[1], K"block", code),

src/scope_analysis.jl

@@ -87,6 +87,13 @@ function find_scope_vars(ex)
     for e in children(ex)
         _find_scope_vars!(assignments, locals, globals, used_names, e)
     end
+
+    # Sort by key so that id generation is deterministic
+    assignments = sort(collect(pairs(assignments)), by=first)
+    locals = sort(collect(pairs(locals)), by=first)
+    globals = sort(collect(pairs(globals)), by=first)
+    used_names = sort(collect(used_names))
+
     return assignments, locals, globals, used_names
 end
 
@@ -98,6 +105,10 @@ struct VarKey
     layer::LayerId
 end
 
+function Base.isless(a::VarKey, b::VarKey)
+    (a.name, a.layer) < (b.name, b.layer)
+end
+
 # Identifiers produced by lowering will have the following layer by default.
 #
 # To make new mutable variables without colliding names, lowering can
@@ -227,9 +238,10 @@ function analyze_scope(ctx, ex, scope_type, lambda_info)
         end
     end
 
+    global_keys = Set(first(g) for g in globals)
     # Add explicit locals
-    for (varkey,e) in pairs(locals)
-        if haskey(globals, varkey)
+    for (varkey,e) in locals
+        if varkey in global_keys
             throw(LoweringError(e, "Variable `$(varkey.name)` declared both local and global"))
         elseif haskey(var_ids, varkey)
             vk = ctx.var_info[var_ids[varkey]].kind
@@ -245,7 +257,7 @@ function analyze_scope(ctx, ex, scope_type, lambda_info)
     end
 
     # Add explicit globals
-    for (varkey,e) in pairs(globals)
+    for (varkey,e) in globals
         if haskey(var_ids, varkey)
             vk = ctx.var_info[var_ids[varkey]].kind
             if vk === :argument && is_outer_lambda_scope

test/branching.jl

@@ -209,4 +209,92 @@ let a = false, b = false
 end
 """) === 3
 
+#-------------------------------------------------------------------------------
+# Detailed lowering
+
+@test ir_as_text(test_mod, """
+begin
+    local a, b
+    if a
+        b
+    end
+end
+""") == """
+slot.₁/a
+(gotoifnot ssa.₁ label.₅)
+slot.₂/b
+(return ssa.₃)
+core.nothing
+(return ssa.₅)"""
+
+@test ir_as_text(test_mod, """
+begin
+    local a, b, c
+    if a
+        b
+    end
+    c
+end
+""") == """
+slot.₁/a
+(gotoifnot ssa.₁ label.₄)
+slot.₂/b
+slot.₃/c
+(return ssa.₄)"""
+
+@test ir_as_text(test_mod, """
+begin
+    local a, b, c
+    if a
+        b
+    else
+        c
+    end
+end
+""") == """
+slot.₁/a
+(gotoifnot ssa.₁ label.₅)
+slot.₂/b
+(return ssa.₃)
+slot.₃/c
+(return ssa.₅)"""
+
+@test ir_as_text(test_mod, """
+begin
+    local a, b, c, d
+    if a
+        b
+    else
+        c
+    end
+    d
+end
+""") == """
+slot.₁/a
+(gotoifnot ssa.₁ label.₅)
+slot.₂/b
+(goto label.₆)
+slot.₃/c
+slot.₄/d
+(return ssa.₆)"""
+
+# Blocks compile directly to branches
+@test ir_as_text(test_mod, """
+begin
+   local a, b, c, d
+   if (a; b && c)
+       d
+   end
+end
+""") == """
+slot.₁/a
+slot.₂/b
+(gotoifnot ssa.₂ label.₈)
+slot.₃/c
+(gotoifnot ssa.₄ label.₈)
+slot.₄/d
+(return ssa.₆)
+core.nothing
+(return ssa.₈)"""
+
 end

test/demo.jl

@@ -207,24 +207,26 @@ M.@recursive 3
 # end
 # """
 
-# src = """
-# let
-#     y = 0
-#     x = 1
-#     let x = x + 1
-#         y = x
-#     end
-#     (x, y)
-# end
-# """
+src = """
+let
+    y = 0
+    x = 1
+    let x = x + 1
+        y = x
+    end
+    (x, y)
+end
+"""
 
 #src = """M.@outer"""
 
 src = """
 begin
-    local a, b
+    local a, b, c
     if a
         b
+    else
+        c
     end
 end
 """