During byte-code generation, strive to avoid jumps that merely jump to the

following instruction.

FossilOrigin-Name: bcf876e67e75f6709f2b25683a3952bbbb87c672bb9d7af456feebc0ab9f6c31

6 files changed, 37 insertions, 4 deletions

diff --git a/src/delete.c b/src/delete.c
index 0a83f1b64..60efc9d56 100644
--- a/src/delete.c
+++ b/src/delete.c
@@ -533,7 +533,9 @@ void sqlite3DeleteFrom(
                                  iTabCur, aToOpen, &iDataCur, &iIdxCur);
       assert( pPk || IsVirtual(pTab) || iDataCur==iTabCur );
       assert( pPk || IsVirtual(pTab) || iIdxCur==iDataCur+1 );
-      if( eOnePass==ONEPASS_MULTI ) sqlite3VdbeJumpHere(v, iAddrOnce);
+      if( eOnePass==ONEPASS_MULTI ){
+        sqlite3VdbeJumpHereOrPopInst(v, iAddrOnce);
+      }
     }
   
     /* Set up a loop over the rowids/primary-keys that were found in the
diff --git a/src/fkey.c b/src/fkey.c
index 9698d343c..7bc20fed0 100644
--- a/src/fkey.c
+++ b/src/fkey.c
@@ -658,7 +658,7 @@ static void fkScanChildren(
   /* Clean up the WHERE clause constructed above. */
   sqlite3ExprDelete(db, pWhere);
   if( iFkIfZero ){
-    sqlite3VdbeJumpHere(v, iFkIfZero);
+    sqlite3VdbeJumpHereOrPopInst(v, iFkIfZero);
   }
 }
 
diff --git a/src/select.c b/src/select.c
index 595b6eb6b..6f8d45c4e 100644
--- a/src/select.c
+++ b/src/select.c
@@ -5493,7 +5493,7 @@ static void updateAccumulator(Parse *pParse, int regAcc, AggInfo *pAggInfo){
 
   pAggInfo->directMode = 0;
   if( addrHitTest ){
-    sqlite3VdbeJumpHere(v, addrHitTest);
+    sqlite3VdbeJumpHereOrPopInst(v, addrHitTest);
   }
 }
 
diff --git a/src/update.c b/src/update.c
index 61b1740b4..d54a6cb9f 100644
--- a/src/update.c
+++ b/src/update.c
@@ -616,7 +616,9 @@ void sqlite3Update(
       }
       sqlite3OpenTableAndIndices(pParse, pTab, OP_OpenWrite, 0, iBaseCur,
                                  aToOpen, 0, 0);
-      if( addrOnce ) sqlite3VdbeJumpHere(v, addrOnce);
+      if( addrOnce ){
+        sqlite3VdbeJumpHereOrPopInst(v, addrOnce);
+      }
     }
   
     /* Top of the update loop */
diff --git a/src/vdbe.h b/src/vdbe.h
index bfde25873..482331eff 100644
--- a/src/vdbe.h
+++ b/src/vdbe.h
@@ -230,6 +230,7 @@ void sqlite3VdbeChangeP2(Vdbe*, int addr, int P2);
 void sqlite3VdbeChangeP3(Vdbe*, int addr, int P3);
 void sqlite3VdbeChangeP5(Vdbe*, u16 P5);
 void sqlite3VdbeJumpHere(Vdbe*, int addr);
+void sqlite3VdbeJumpHereOrPopInst(Vdbe*, int addr);
 int sqlite3VdbeChangeToNoop(Vdbe*, int addr);
 int sqlite3VdbeDeletePriorOpcode(Vdbe*, u8 op);
 #ifdef SQLITE_DEBUG
diff --git a/src/vdbeaux.c b/src/vdbeaux.c
index 52959a43e..2a4741573 100644
--- a/src/vdbeaux.c
+++ b/src/vdbeaux.c
@@ -1065,6 +1065,34 @@ void sqlite3VdbeJumpHere(Vdbe *p, int addr){
   sqlite3VdbeChangeP2(p, addr, p->nOp);
 }
 
+/*
+** Change the P2 operand of the jump instruction at addr so that
+** the jump lands on the next opcode.  Or if the jump instruction was
+** the previous opcode (and is thus a no-op) then simply back up
+** the next instruction counter by one slot so that the jump is
+** overwritten by the next inserted opcode.
+**
+** This routine is an optimization of sqlite3VdbeJumpHere() that
+** strives to omit useless byte-code like this:
+**
+**        7   Once 0 8 0
+**        8   ...
+*/
+void sqlite3VdbeJumpHereOrPopInst(Vdbe *p, int addr){
+  if( addr==p->nOp-1 ){
+    assert( p->aOp[addr].opcode==OP_Once
+         || p->aOp[addr].opcode==OP_If
+         || p->aOp[addr].opcode==OP_FkIfZero );
+    assert( p->aOp[addr].p4type==0 );
+#ifdef SQLITE_VDBE_COVERAGE
+    sqlite3VdbeGetOp(v,-1)->iSrcLine = 0;  /* Erase VdbeCoverage() macros */
+#endif
+    p->nOp--;
+  }else{
+    sqlite3VdbeChangeP2(p, addr, p->nOp);
+  }
+}
+
 
 /*
 ** If the input FuncDef structure is ephemeral, then free it.  If