Small but significant shift optimization

git-svn-id: svn://svn.cc65.org/cc65/trunk@1559 b7a2c559-68d2-44c3-8de9-860c34a00d81

diff --git a/src/cc65/codeopt.c b/src/cc65/codeopt.c
index a1d824d0ac2ea4bc9524e4116de580fc1528b811..01bba7b42369fb00c289939e418c1c3df31de2c9 100644 (file)
--- a/src/cc65/codeopt.c
+++ b/src/cc65/codeopt.c
@@ -138,13 +138,18 @@ static unsigned OptShift1 (CodeSeg* S)
 
 static unsigned OptShift2 (CodeSeg* S)
 /* A call to the shraxN routine may get replaced by one or more lsr insns
- * if the value of X is not used later.
+ * if the value of X is not used later, or if the value of X is known and
+ * zero.
  */
 {
     unsigned Changes = 0;
+    unsigned I;
+
+    /* Generate register info */
+    CS_GenRegInfo (S);
 
     /* Walk over the entries */
-    unsigned I = 0;
+    I = 0;
     while (I < CS_GetEntryCount (S)) {
 
        /* Get next entry */
@@ -155,13 +160,13 @@ static unsigned OptShift2 (CodeSeg* S)
                    strncmp (E->Arg, "shrax", 5) == 0        &&
            strlen (E->Arg) == 6                     &&
            IsDigit (E->Arg[5])                      &&
-           !RegXUsed (S, I+1)) {
+                   (E->RI->In.RegX == 0 || !RegXUsed (S, I+1))) {
 
            /* Insert shift insns */
            unsigned Count = E->Arg[5] - '0';
            while (Count--) {
                CodeEntry* X = NewCodeEntry (OP65_LSR, AM65_ACC, "a", 0, E->LI);
-               CS_InsertEntry (S, X, I+1);
+               CS_InsertEntry (S, X, I+1);
            }
 
            /* Delete the call to shlax */
@@ -177,6 +182,9 @@ static unsigned OptShift2 (CodeSeg* S)
 
     }
 
+    /* Free the register info */
+    CS_FreeRegInfo (S);
+
     /* Return the number of changes made */
     return Changes;
 }