cleaned up substitute_broadcast

Author: mxpoch

src/constructors.jl

@@ -54,30 +54,38 @@ function substitute_broadcast(
   warncheckarg::Int,
   safe::Bool
 )
+  # Lower the expression to get the compiler's intermediate representation (IR).
   ci = first(Meta.lower(LoopVectorization, q).args).code
   nargs = length(ci) - 1
-  lb = Expr(:block)
+  lb = Expr(:block) # This will become the `let` block
   syms = Vector{Symbol}(undef, nargs)
   configarg = (inline, u₁, u₂, v, true, threads, warncheckarg, safe)
   unroll_param_tup =
     Expr(:call, lv(:avx_config_val), :(Val{$configarg}()), staticexpr(0))
 
+  # Iterate through each instruction from the lowered code.
   for n ∈ 1:nargs
     _ciₙ = ci[n]
-    syms[n] = Symbol('%', n)
+    syms[n] = Symbol('%', n) # Temporary variable for this instruction's result
 
-    local rhs
     if _ciₙ isa Core.SSAValue
-      rhs = syms[_ciₙ.id]
+      # Case 1: The instruction is a reference to a previous result.
+      # Create the assignment expression directly.
+      push!(lb.args, Expr(:(=), syms[n], syms[_ciₙ.id]))
 
     elseif _ciₙ isa GlobalRef
+      # Case 2: The instruction is a global reference.
       if _ciₙ.mod === Base || _ciₙ.mod === Core
-        rhs = lv(_ciₙ.name)
+        # It's a base operator like `+`. Qualify it and create the assignment.
+        push!(lb.args, Expr(:(=), syms[n], lv(_ciₙ.name)))
       else
-        rhs = _ciₙ.name
+        # It's a user-defined global (e.g., `a`). Do not qualify it.
+        push!(lb.args, Expr(:(=), syms[n], _ciₙ.name))
       end
 
     elseif _ciₙ isa Expr && _ciₙ.head === :call
+      # Case 3: A function call to be transformed (e.g., `materialize`).
+      # This branch handles its own logic via `add_ci_call!`.
       f = first(_ciₙ.args)
       if isglobalref(f, Base, :materialize!)
         add_ci_call!(lb, lv(:vmaterialize!), _ciₙ.args, syms, n, unroll_param_tup, mod)
@@ -86,16 +94,21 @@ function substitute_broadcast(
       else
         add_ci_call!(lb, f, _ciₙ.args, syms, n)
       end
-      continue
+
     else
-      rhs = _ciₙ
+      # Case 4 (Catch-all): A local variable or a literal value.
+      # Create the assignment directly, leaving the value as is.
+      push!(lb.args, Expr(:(=), syms[n], _ciₙ))
     end
-    push!(lb.args, Expr(:(=), syms[n], rhs))
   end
+
+  # Extract the final return value from the generated `let` block.
   ret::Expr = pop!(lb.args)::Expr
   if Meta.isexpr(ret, :(=), 2)
     ret = (ret.args[2])::Expr
   end
+
+  # Escape the entire `let` block to ensure hygiene for local variables.
   esc(Expr(:let, lb, Expr(:block, ret)))
 end