Minor optimization for 8051 tail increment/decrement

git-svn-id: https://sdcc.svn.sourceforge.net/svnroot/sdcc/trunk/sdcc@105 4a8a32a2-be11-0410-ad9d-d568d2c75423

diff --git a/src/mcs51/gen.c b/src/mcs51/gen.c
index 9c221fc954a7eef1852809060dfb21e197f22b18..93bc1c244b7ccd48e10274543492aeb6589a4a94 100644 (file)
--- a/src/mcs51/gen.c
+++ b/src/mcs51/gen.c
@@ -2248,6 +2248,33 @@ static void genGoto (iCode *ic)
     emitcode ("ljmp","%05d$",(IC_LABEL(ic)->key+100));
 }
 
+/*-----------------------------------------------------------------*/
+/* findLabelBackwards: walks back through the iCode chain looking  */
+/* for the given label. Returns number of iCode instructions      */
+/* between that label and given ic.                               */
+/* Returns zero if label not found.                               */
+/*-----------------------------------------------------------------*/
+static int findLabelBackwards(iCode *ic, int key)
+{
+    int count = 0;
+    
+    while (ic->prev)
+    {
+        ic = ic->prev;
+        count++;
+        
+        if (ic->op == LABEL && IC_LABEL(ic)->key == key)
+        {
+            printf("findLabelBackwards = %d\n", count);
+            return count;
+        }
+    }
+    
+    printf("findLabelBackwards: not found.\n");
+    
+    return 0;
+}
+
 /*-----------------------------------------------------------------*/
 /* genPlusIncr :- does addition with increment if possible         */
 /*-----------------------------------------------------------------*/
@@ -2271,7 +2298,27 @@ static bool genPlusIncr (iCode *ic)
     if (sameRegs(AOP(IC_LEFT(ic)), AOP(IC_RESULT(ic))) &&
         (size > 1) &&
         (icount == 1)) {
-        symbol *tlbl = newiTempLabel(NULL);
+        symbol *tlbl;
+        int emitTlbl;
+        int labelRange;
+
+       /* If the next instruction is a goto and the goto target
+        * is < 10 instructions previous to this, we can generate
+        * jumps straight to that target.
+        */
+        if (ic->next && ic->next->op == GOTO
+            && (labelRange = findLabelBackwards(ic, IC_LABEL(ic->next)->key)) != 0
+            && labelRange <= 10 )
+        {
+           emitcode(";", "tail increment optimized");
+           tlbl = IC_LABEL(ic->next);
+           emitTlbl = 0;
+        }
+        else
+        {
+            tlbl = newiTempLabel(NULL);
+            emitTlbl = 1;
+        }
        emitcode("inc","%s",aopGet(AOP(IC_RESULT(ic)),LSB,FALSE,FALSE));
        if(AOP_TYPE(IC_RESULT(ic)) == AOP_REG ||
           IS_AOP_PREG(IC_RESULT(ic)))
@@ -2314,7 +2361,11 @@ static bool genPlusIncr (iCode *ic)
            }
            emitcode("inc","%s",aopGet(AOP(IC_RESULT(ic)),MSB32,FALSE,FALSE));
        }
-       emitcode("","%05d$:",tlbl->key+100);
+       
+       if (emitTlbl)
+       {
+           emitcode("","%05d$:",tlbl->key+100);
+       }
         return TRUE;
     }
     
@@ -2548,7 +2599,7 @@ release:
 static bool genMinusDec (iCode *ic)
 {
     unsigned int icount ;
-       unsigned int size = getDataSize(IC_RESULT(ic));
+    unsigned int size = getDataSize(IC_RESULT(ic));
 
     /* will try to generate an increment */
     /* if the right side is not a literal 
@@ -2561,12 +2612,32 @@ static bool genMinusDec (iCode *ic)
     if ((icount = (unsigned int) floatFromVal (AOP(IC_RIGHT(ic))->aopu.aop_lit)) > 4)
         return FALSE ;
 
-       size = getDataSize(IC_RESULT(ic));
     /* if decrement 16 bits in register */
     if (sameRegs(AOP(IC_LEFT(ic)), AOP(IC_RESULT(ic))) &&
         (size > 1) &&
         (icount == 1)) {
-        symbol *tlbl = newiTempLabel(NULL);
+            symbol *tlbl;
+            int emitTlbl;
+            int labelRange;
+
+           /* If the next instruction is a goto and the goto target
+            * is <= 10 instructions previous to this, we can generate
+            * jumps straight to that target.
+            */
+            if (ic->next && ic->next->op == GOTO
+                && (labelRange = findLabelBackwards(ic, IC_LABEL(ic->next)->key)) != 0
+                && labelRange <= 10 )
+            {        
+               emitcode(";", "tail decrement optimized");
+               tlbl = IC_LABEL(ic->next);
+               emitTlbl = 0;
+            }
+            else
+            {
+                tlbl = newiTempLabel(NULL);
+                emitTlbl = 1;
+            }
+        
                emitcode("dec","%s",aopGet(AOP(IC_RESULT(ic)),LSB,FALSE,FALSE));
                if(AOP_TYPE(IC_RESULT(ic)) == AOP_REG ||
                   IS_AOP_PREG(IC_RESULT(ic)))
@@ -2608,7 +2679,10 @@ static bool genMinusDec (iCode *ic)
                        }
                        emitcode("dec","%s",aopGet(AOP(IC_RESULT(ic)),MSB32,FALSE,FALSE));
                }
-               emitcode("","%05d$:",tlbl->key+100);
+               if (emitTlbl)
+               {
+                   emitcode("","%05d$:",tlbl->key+100);
+               }
         return TRUE;
     }