Performance optimization: avoid unnecessary calls to computeLimitRegisters().

FossilOrigin-Name: f48bd8f85d86fd93329dda7ba57f468854a732b89e4126e9c5beec3495d24b31

manifest

@@ -1,5 +1,5 @@
-C Fix\san\sassert()\sthat\swas\smade\sout-of-date\sby\s[b52393ac28debe98].
-D 2022-07-25T23:34:14.245
+C Performance\soptimization:\s\savoid\sunnecessary\scalls\sto\scomputeLimitRegisters().
+D 2022-07-26T01:20:18.198
 F .fossil-settings/empty-dirs dbb81e8fc0401ac46a1491ab34a7f2c7c0452f2f06b54ebb845d024ca8283ef1
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 F LICENSE.md df5091916dbb40e6e9686186587125e1b2ff51f022cc334e886c19a0e9982724
@@ -570,7 +570,7 @@ F src/printf.c e99ee9741e79ae3873458146f59644276657340385ade4e76a5f5d1c25793764
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 F src/rowset.c ba9515a922af32abe1f7d39406b9d35730ed65efab9443dc5702693b60854c92
-F src/select.c a9516e1453241986f1eb73c00a0e7cf23d23081fd2eb50e67fcbb96fe7bf6f00
+F src/select.c 2219591ff134d612e2e3e9d401665634bac45956f2c12100280c04efb0d99bb8
 F src/shell.c.in 29749b34bbd19d0004fdb6f61f62659096e1c0b4dfb1ad2314e7fafbe9dd8d37
 F src/sqlite.h.in be265991edca9aea69986758b58ba81cbf5ae403fe0c4ea1d0c9df0cdc8f25ed
 F src/sqlite3.rc 5121c9e10c3964d5755191c80dd1180c122fc3a8
@@ -1981,8 +1981,8 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
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 U drh
-Z a20715ac16e756fff0bd1afe1caf81e7
+Z 3b35c17a3beaeddc52e4b88d9f02979e
 # Remove this line to create a well-formed Fossil manifest.

manifest.uuid

@@ -1 +1 @@
-db8230e80ed894fc2801cdbb53c2cd9de00192d7f4d8328c29cc214e2e0adde9
+f48bd8f85d86fd93329dda7ba57f468854a732b89e4126e9c5beec3495d24b31

src/select.c

@@ -7196,7 +7196,7 @@ int sqlite3Select(
   if( (p->selFlags & SF_FixedLimit)==0 ){
     p->nSelectRow = 320;  /* 4 billion rows */
   }
-  computeLimitRegisters(pParse, p, iEnd);
+  if( p->pLimit ) computeLimitRegisters(pParse, p, iEnd);
   if( p->iLimit==0 && sSort.addrSortIndex>=0 ){
     sqlite3VdbeChangeOpcode(v, sSort.addrSortIndex, OP_SorterOpen);
     sSort.sortFlags |= SORTFLAG_UseSorter;