OptCmp3 removed a compare to zero instruction preceeded by a load despite the

fact that the carry flag (which is set by the compare but not by the load) had
been used later.

git-svn-id: svn://svn.cc65.org/cc65/trunk@5885 b7a2c559-68d2-44c3-8de9-860c34a00d81

diff --git a/src/cc65/coptcmp.c b/src/cc65/coptcmp.c
index b99c1a69a48c544d0829ad63f83351bca560ba52..25e1a8982c7bfbfeac78b8a99db6f52afea2f547 100644 (file)
--- a/src/cc65/coptcmp.c
+++ b/src/cc65/coptcmp.c
@@ -432,8 +432,8 @@ unsigned OptCmp3 (CodeSeg* S)
             int Delete = 0;
 
            /* Check for the call to boolxx. We only remove the compare if
-            * the carry flag is evaluated later, because the load will not
-            * set the carry flag.
+                    * the carry flag is not evaluated later, because the load will
+             * not set the carry flag.
             */
            if (L[2]->OPC == OP65_JSR) {
                switch (FindBoolCmpCond (L[2]->Arg)) {
@@ -458,12 +458,29 @@ unsigned OptCmp3 (CodeSeg* S)
                }
 
            } else if ((L[2]->Info & OF_FBRA) != 0) {
-
-                /* The following insn branches on the condition of a load, so
-                 * the compare instruction can be removed.
+                /* The following insn branches on the condition of the load,
+                 * so the compare instruction might be removed. For safety,
+                 * do some more checks if the carry isn't used later, since
+                 * the compare does set the carry, but the load does not.
                  */
-                Delete = 1;
-
+                CodeEntry* E;
+                CodeEntry* N;
+                if ((E = CS_GetNextEntry (S, I+2)) != 0         &&
+                    L[2]->JumpTo != 0                           &&
+                    (N = L[2]->JumpTo->Owner) != 0              &&
+                    N->OPC != OP65_BCC                          &&
+                    N->OPC != OP65_BCS                          &&
+                    N->OPC != OP65_JCC                          &&
+                    N->OPC != OP65_JCS                          &&
+                    (N->OPC != OP65_JSR                 ||
+                    FindBoolCmpCond (N->Arg) == CMP_INV)) {
+
+                    /* The following insn branches on the condition of a load,
+                     * and there's no use of the carry flag in sight, so the
+                     * compare instruction can be removed.
+                     */
+                    Delete = 1;
+                }
             }
 
             /* Delete the compare if we can */