From: kvigor <kvigor@4a8a32a2-be11-0410-ad9d-d568d2c75423>
Date: Fri, 18 Apr 2003 21:03:51 +0000 (+0000)
Subject: optimization: replace modulo by a power of two with a bitwise AND
X-Git-Url: https://git.gag.com/?a=commitdiff_plain;h=0259910eb50f7d13e3d45da7a8ae230a10d56da1;p=fw%2Fsdcc

optimization: replace modulo by a power of two with a bitwise AND


git-svn-id: https://sdcc.svn.sourceforge.net/svnroot/sdcc/trunk/sdcc@2538 4a8a32a2-be11-0410-ad9d-d568d2c75423
---

diff --git a/ChangeLog b/ChangeLog
index e98bb7b6..2ebb0997 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+2003-04-18 	Kevin Vigor <kevin@vigor.nu>
+
+	* src/SDCCopt.c: add special case optimization to replace modulo by
+	  a power of two with a bitwise AND.
+
 2003-04-18    <johan@balder>
 
 	* src/mcs51/gen.c (getFreePtr): fixed bug #635354
diff --git a/src/SDCCopt.c b/src/SDCCopt.c
index fd7fadc6..2e1ff9a6 100644
--- a/src/SDCCopt.c
+++ b/src/SDCCopt.c
@@ -324,6 +324,8 @@ found:
 
 }
 
+extern operand *geniCodeRValue (operand *, bool);
+
 /*-----------------------------------------------------------------*/
 /* convilong - converts int or long mults or divs to fcalls        */
 /*-----------------------------------------------------------------*/
@@ -338,8 +340,34 @@ convilong (iCode * ic, eBBlock * ebp, sym_link * type, int op)
   int su;
   int bytesPushed=0;
 
-  remiCodeFromeBBlock (ebp, ic);
-
+  // Easy special case which avoids function call: modulo by a literal power 
+  // of two can be replaced by a bitwise AND.
+  if (op == '%' && isOperandLiteral(IC_RIGHT(ic)))
+  {
+      unsigned litVal = (unsigned)(operandLitValue(IC_RIGHT(ic)));
+      
+      // See if literal value is a power of 2.
+      while (litVal && !(litVal & 1))
+      {
+	  litVal >>= 1;
+      }
+      if (litVal)
+      {
+	  // discard first high bit set.
+	  litVal >>= 1;
+      }
+	  
+      if (!litVal)
+      {
+	  ic->op = BITWISEAND;
+	  IC_RIGHT(ic) = operandFromLit(operandLitValue(IC_RIGHT(ic)) - 1);
+	  return;
+      }
+  }
+    
+  remiCodeFromeBBlock (ebp, ic);    
+    
+    
   /* depending on the type */
   for (bwd = 0; bwd < 3; bwd++)
     {