fix read and write calls: save and restore ecx and edx

src/X86.lama

@@ -164,7 +164,23 @@ fun makeEnv (stack, stackSlots, globals) {
     stackSlots
   }
 
-  [envString, allocate, push, pop, pop2, addGlobal, loc, getGlobals, getStackSize]
+  (* generates code that 
+     1. saves two caller-saved registers (ecx, edx),
+     2. adds @push_args_code,
+     3. calls function @func_name,
+     4. adds @addl_code
+     5. restores registers
+  *)
+  fun genCallF (func_name, push_args_code, addl_code) {
+    emptyBuffer() 
+      <+  Push (ecx) <+ Push (edx)
+      <+> push_args_code
+      <+  Call (func_name)
+      <+> addl_code
+      <+  Pop  (ecx) <+ Pop  (edx)
+  }
+
+  [envString, allocate, push, pop, pop2, addGlobal, loc, getGlobals, getStackSize, genCallF]
 }
 
 -- Exported accessors
@@ -204,6 +220,10 @@ fun getStackSize (env) {
   env [8] ()
 }
 
+fun genCallF (env, func_name, push_args_code, addl_code) {
+  env [9] (func_name, push_args_code, addl_code)
+}
+
 -- Creates an initial environment
 fun initEnv () {
   makeEnv (0, emptySet (compare), emptySet (compare))
@@ -288,11 +308,11 @@ fun compile (env, code) {
       case i of
         READ ->
           case env.allocate of
-            [s, env] -> [env, code <+ Call ("Lread") <+ Mov (eax, s)]
+            [s, env] -> [env, code <+> genCallF(env, "Lread", emptyBuffer(), emptyBuffer()) <+ Mov (eax, s)]
           esac             
       | WRITE ->
           case env.pop of
-            [s, env] -> [env, code <+ Push (s) <+ Call ("Lwrite") <+ Pop (eax)]
+            [s, env] -> [env, code <+> genCallF(env, "Lwrite", singletonBuffer(Push(s)), singletonBuffer(Pop (eax)))]
           esac
       | _ -> failure ("codegeneration for instruction %s is not yet implemented\n", i.string)
         esac