docs: clarify evalExprOntoStack sanity check, explanation comments for generateCall

src/main/wacc/backend/asmGenerator.scala

@@ -372,7 +372,10 @@ object asmGenerator {
         asm += stack.push(call.ty.size, RAX)
     }
 
-    assert(stack.size == stackSizeStart + 1)
+    assert(
+      stack.size == stackSizeStart + 1,
+      "Sanity check: ONLY the evaluated expression should have been pushed onto the stack"
+    )
     asm ++= zeroRest(MemLocation(stack.head.pointer, Q64), expr.ty.size)
     asm
   }
@@ -384,17 +387,20 @@ object asmGenerator {
     var asm = Chain.empty[AsmLine]
     val microWacc.Call(target, args) = call
 
+    // Evaluate arguments 0-6
     argRegs
       .zip(args)
       .map { (reg, expr) =>
         asm ++= evalExprOntoStack(expr)
         reg
       }
+      // And set the appropriate registers
       .reverse
       .foreach { reg =>
         asm += stack.pop(Register(Q64, reg))
       }
 
+    // Evaluate arguments 7 and up and push them onto the stack
     args.drop(argRegs.size).foldMap {
       asm ++= evalExprOntoStack(_)
     }
@@ -406,6 +412,7 @@ object asmGenerator {
       asm += assemblyIR.Call(labelGenerator.getLabelArg(target)) // regular call
     }
 
+    // Remove arguments 7 and up from the stack
     if (args.size > argRegs.size) {
       asm += stack.drop(args.size - argRegs.size)
     }