Cleaned up the code used for handling jump labels and the label name.

Fixed a problem that caused the optimizer not to detect that flags set by
a load are used, if the use is "hidden" behind an unconditional branch. This
caused the optimizer to remove the load.


git-svn-id: svn://svn.cc65.org/cc65/trunk@3111 b7a2c559-68d2-44c3-8de9-860c34a00d81

src/cc65/codeent.c

@@ -323,6 +323,22 @@ void CE_AttachLabel (CodeEntry* E, CodeLabel* L)
 
 
 
+void CE_ClearJumpTo (CodeEntry* E)
+/* Clear the JumpTo entry and the argument (which contained the name of the
+ * label). Note: The function will not clear the backpointer from the label,
+ * so use it with care.
+ */
+{
+    /* Clear the JumpTo entry */
+    E->JumpTo = 0;
+
+    /* Clear the argument and assign the empty one */
+    FreeArg (E->Arg);
+    E->Arg = EmptyArg;
+}
+
+
+
 void CE_MoveLabel (CodeLabel* L, CodeEntry* E)
 /* Move the code label L from it's former owner to the code entry E. */
 {
@@ -391,6 +407,33 @@ int CE_UseLoadFlags (const CodeEntry* E)
  * a register (N and Z).
  */
 {
+    /* Follow unconditional branches, but beware of endless loops. After this,
+     * E will point to the first entry that is not a branch.
+     */
+    if (E->Info & OF_UBRA) {
+        Collection C = AUTO_COLLECTION_INITIALIZER;
+
+        /* Follow the chain */
+        while (E->Info & OF_UBRA) {
+
+            /* Remember the entry so we can detect loops */
+            CollAppend (&C, (void*) E);
+
+            /* Check the target */
+            if (E->JumpTo == 0 || CollIndex (&C, E->JumpTo->Owner) >= 0) {
+                /* Unconditional jump to external symbol, or endless loop. */
+                DoneCollection (&C);
+                return 0;       /* Flags not used */
+            }
+
+            /* Follow the chain */
+            E = E->JumpTo->Owner;
+        }
+
+        /* Delete the collection */
+        DoneCollection (&C);
+    }
+
     /* A branch will use the flags */
     if (E->Info & OF_FBRA) {
         return 1;
@@ -429,7 +472,7 @@ void CE_FreeRegInfo (CodeEntry* E)
 /* Free an existing register info struct */
 {
     if (E->RI) {
-	FreeRegInfo (E->RI);
+       	FreeRegInfo (E->RI);
 	E->RI = 0;
     }
 }

src/cc65/codeent.h

@@ -115,6 +115,12 @@ int CodeEntriesAreEqual (const CodeEntry* E1, const CodeEntry* E2);
 void CE_AttachLabel (CodeEntry* E, CodeLabel* L);
 /* Attach the label to the entry */
 
+void CE_ClearJumpTo (CodeEntry* E);
+/* Clear the JumpTo entry and the argument (which contained the name of the
+ * label). Note: The function will not clear the backpointer from the label,
+ * so use it with care.
+ */
+
 #if defined(HAVE_INLINE)
 INLINE int CE_HasLabel (const CodeEntry* E)
 /* Check if the given code entry has labels attached */

src/cc65/codeseg.c

@@ -829,7 +829,7 @@ void CS_DelLabel (CodeSeg* S, CodeLabel* L)
        	/* Get the insn referencing this label */
        	CodeEntry* E = CollAt (&L->JumpFrom, I);
        	/* Remove the reference */
-       	E->JumpTo = 0;
+       	CE_ClearJumpTo (E);
     }
     CollDeleteAll (&L->JumpFrom);
 
@@ -875,7 +875,10 @@ void CS_MergeLabels (CodeSeg* S)
 	       	for (J = 0; J < CL_GetRefCount (X); ++J) {
 		    /* Get the entry referencing this label */
 		    CodeEntry* E = CL_GetRef (X, J);
-		    /* And remove the reference */
+		    /* And remove the reference. Do NOT call CE_ClearJumpTo
+                     * here, because this will also clear the label name,
+                     * which is not what we want.
+                     */
 		    E->JumpTo = 0;
 	   	}
 
@@ -999,7 +1002,7 @@ void CS_RemoveLabelRef (CodeSeg* S, struct CodeEntry* E)
     CollDeleteItem (&L->JumpFrom, E);
 
     /* The entry jumps no longer to L */
-    E->JumpTo = 0;
+    CE_ClearJumpTo (E);
 
     /* If there are no more references, delete the label */
     if (CollCount (&L->JumpFrom) == 0) {