Optimizations to the main loop inside sqlite3VdbeExec() to help VDBE byte code

run a few percent faster.

FossilOrigin-Name: d622ac6ac7a297754494d3a33dbaeea02836272e

src/vdbe.h

@@ -42,7 +42,7 @@ typedef struct SubProgram SubProgram;
 struct VdbeOp {
   u8 opcode;          /* What operation to perform */
   signed char p4type; /* One of the P4_xxx constants for p4 */
-  u8 opflags;         /* Not currently used */
+  u8 opflags;         /* Mask of the OPFLG_* flags in opcodes.h */
   u8 p5;              /* Fifth parameter is an unsigned character */
   int p1;             /* First operand */
   int p2;             /* Second parameter (often the jump destination) */