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

manifest

@@ -1,5 +1,5 @@
-C Avoid\sallocating\sspace\sto\shold\sthe\sprepared\sstatements\sfor\sCREATE\sstatements\nwhen\sparsing\sthe\sschema\sof\san\sexisting\sdatabase,\ssince\sthose\sprepared\nstatements\sare\snever\sused..\s\sThis\shelps\sto\smake\sstartup\sfaster,
-D 2021-01-01T22:06:17.152
+C In\sLemon,\sfactor\sthe\sparser\sstack\soverflow\sdetection\slogic\sout\sof\sthe\nyy_reduce()\ssubroutine\sand\sinto\sthe\smain\sparser\sroutine,\sso\sthat\swhen\soverflow\nis\sdetected,\sit\scan\sexit\simmediately.\s\sThis\ssaves\sa\ssingle\sconditional\sin\nthe\smain\sloop\sof\sthe\sparser.
+D 2021-01-02T23:56:37.261
 F .fossil-settings/empty-dirs dbb81e8fc0401ac46a1491ab34a7f2c7c0452f2f06b54ebb845d024ca8283ef1
 F .fossil-settings/ignore-glob 35175cdfcf539b2318cb04a9901442804be81cd677d8b889fcc9149c21f239ea
 F LICENSE.md df5091916dbb40e6e9686186587125e1b2ff51f022cc334e886c19a0e9982724
@@ -1815,7 +1815,7 @@ F tool/getlock.c f4c39b651370156cae979501a7b156bdba50e7ce
 F tool/index_usage.c f62a0c701b2c7ff2f3e21d206f093c123f222dbf07136a10ffd1ca15a5c706c5
 F tool/kvtest-speed.sh 4761a9c4b3530907562314d7757995787f7aef8f
 F tool/lemon.c 70eedc31614a58fe31a71025c17ebd1502a6ce9cfef0ed5e33acb0b5b737b291
-F tool/lempar.c 0e1d5eeb9736108d3dba782a9dd56f4e7cb69006b6ee181308b7ebfb15313a12
+F tool/lempar.c 1d3d075da18681c67ecc66c1f171e7094e18cd2cfba6a8a1bd4f3f639d6656e1
 F tool/libvers.c caafc3b689638a1d88d44bc5f526c2278760d9b9
 F tool/loadfts.c c3c64e4d5e90e8ba41159232c2189dba4be7b862
 F tool/logest.c 11346aa019e2e77a00902aa7d0cabd27bd2e8cca
@@ -1895,7 +1895,7 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
 F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
 F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
-P 76de2bb04b1c02a6c0300cd61d9b3d2477d845aa0d1cdb9dbe4f354b9fedd923
-R df14a0f8e3c8c0f24b4bc5fa275286c3
+P d01e9f2d00dc439c529cd8885a219fcddbaad73b9f471b020e2a0c18e2add69b
+R 30317f78042211a4eaf8fdf4d0539bb2
 U drh
-Z f56f3715fca7ebd8ed5abb62c2ed9411
+Z 16a40d4bd4688bf574b37b863bb32871

manifest.uuid

@@ -1 +1 @@
-d01e9f2d00dc439c529cd8885a219fcddbaad73b9f471b020e2a0c18e2add69b
+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;