In Lemon, factor the parser stack overflow detection logic out of the

yy_reduce() subroutine and into the main parser routine, so that when overflow
is detected, it can exit immediately.  This saves a single conditional in
the main loop of the parser.

FossilOrigin-Name: 203c049c662380411522d0c7c493201331bbb2792a7c5b12684f04f532a0695d

tool/lempar.c

@@ -718,55 +718,6 @@ static YYACTIONTYPE yy_reduce(
   (void)yyLookahead;
   (void)yyLookaheadToken;
   yymsp = yypParser->yytos;
-  assert( yyruleno<(int)(sizeof(yyRuleName)/sizeof(yyRuleName[0])) );
-#ifndef NDEBUG
-  if( yyTraceFILE ){
-    yysize = yyRuleInfoNRhs[yyruleno];
-    if( yysize ){
-      fprintf(yyTraceFILE, "%sReduce %d [%s]%s, pop back to state %d.\n",
-        yyTracePrompt,
-        yyruleno, yyRuleName[yyruleno],
-        yyruleno<YYNRULE_WITH_ACTION ? "" : " without external action",
-        yymsp[yysize].stateno);
-    }else{
-      fprintf(yyTraceFILE, "%sReduce %d [%s]%s.\n",
-        yyTracePrompt, yyruleno, yyRuleName[yyruleno],
-        yyruleno<YYNRULE_WITH_ACTION ? "" : " without external action");
-    }
-  }
-#endif /* NDEBUG */
-
-  /* Check that the stack is large enough to grow by a single entry
-  ** if the RHS of the rule is empty.  This ensures that there is room
-  ** enough on the stack to push the LHS value */
-  if( yyRuleInfoNRhs[yyruleno]==0 ){
-#ifdef YYTRACKMAXSTACKDEPTH
-    if( (int)(yypParser->yytos - yypParser->yystack)>yypParser->yyhwm ){
-      yypParser->yyhwm++;
-      assert( yypParser->yyhwm == (int)(yypParser->yytos - yypParser->yystack));
-    }
-#endif
-#if YYSTACKDEPTH>0 
-    if( yypParser->yytos>=yypParser->yystackEnd ){
-      yyStackOverflow(yypParser);
-      /* The call to yyStackOverflow() above pops the stack until it is
-      ** empty, causing the main parser loop to exit.  So the return value
-      ** is never used and does not matter. */
-      return 0;
-    }
-#else
-    if( yypParser->yytos>=&yypParser->yystack[yypParser->yystksz-1] ){
-      if( yyGrowStack(yypParser) ){
-        yyStackOverflow(yypParser);
-        /* The call to yyStackOverflow() above pops the stack until it is
-        ** empty, causing the main parser loop to exit.  So the return value
-        ** is never used and does not matter. */
-        return 0;
-      }
-      yymsp = yypParser->yytos;
-    }
-#endif
-  }
 
   switch( yyruleno ){
   /* Beginning here are the reduction cases.  A typical example
@@ -925,12 +876,56 @@ void Parse(
   }
 #endif
 
-  do{
+  while(1){ /* Exit by "break" */
+    assert( yypParser->yytos>=yypParser->yystack );
     assert( yyact==yypParser->yytos->stateno );
     yyact = yy_find_shift_action((YYCODETYPE)yymajor,yyact);
     if( yyact >= YY_MIN_REDUCE ){
-      yyact = yy_reduce(yypParser,yyact-YY_MIN_REDUCE,yymajor,
-                        yyminor ParseCTX_PARAM);
+      unsigned int yyruleno = yyact - YY_MIN_REDUCE; /* Reduce by this rule */
+      assert( yyruleno<(int)(sizeof(yyRuleName)/sizeof(yyRuleName[0])) );
+#ifndef NDEBUG
+      if( yyTraceFILE ){
+        int yysize = yyRuleInfoNRhs[yyruleno];
+        if( yysize ){
+          fprintf(yyTraceFILE, "%sReduce %d [%s]%s, pop back to state %d.\n",
+            yyTracePrompt,
+            yyruleno, yyRuleName[yyruleno],
+            yyruleno<YYNRULE_WITH_ACTION ? "" : " without external action",
+            yypParser->yytos[yysize].stateno);
+        }else{
+          fprintf(yyTraceFILE, "%sReduce %d [%s]%s.\n",
+            yyTracePrompt, yyruleno, yyRuleName[yyruleno],
+            yyruleno<YYNRULE_WITH_ACTION ? "" : " without external action");
+        }
+      }
+#endif /* NDEBUG */
+
+      /* Check that the stack is large enough to grow by a single entry
+      ** if the RHS of the rule is empty.  This ensures that there is room
+      ** enough on the stack to push the LHS value */
+      if( yyRuleInfoNRhs[yyruleno]==0 ){
+#ifdef YYTRACKMAXSTACKDEPTH
+        if( (int)(yypParser->yytos - yypParser->yystack)>yypParser->yyhwm ){
+          yypParser->yyhwm++;
+          assert( yypParser->yyhwm ==
+                  (int)(yypParser->yytos - yypParser->yystack));
+        }
+#endif
+#if YYSTACKDEPTH>0 
+        if( yypParser->yytos>=yypParser->yystackEnd ){
+          yyStackOverflow(yypParser);
+          break;
+        }
+#else
+        if( yypParser->yytos>=&yypParser->yystack[yypParser->yystksz-1] ){
+          if( yyGrowStack(yypParser) ){
+            yyStackOverflow(yypParser);
+            break;
+          }
+        }
+#endif
+      }
+      yyact = yy_reduce(yypParser,yyruleno,yymajor,yyminor ParseCTX_PARAM);
     }else if( yyact <= YY_MAX_SHIFTREDUCE ){
       yy_shift(yypParser,yyact,(YYCODETYPE)yymajor,yyminor);
 #ifndef YYNOERRORRECOVERY
@@ -1043,7 +1038,7 @@ void Parse(
       break;
 #endif
     }
-  }while( yypParser->yytos>yypParser->yystack );
+  }
 #ifndef NDEBUG
   if( yyTraceFILE ){
     yyStackEntry *i;