Alternative implementation of the comparison opcode speed-up of

check-in [4a8805d9a66dc888] that should pass muster with UBSAN.

FossilOrigin-Name: afb18f64541effaeaada2d72c7c91adfe5ec3e2b1418c0bc281083125fb5badb

3 files changed, 36 insertions, 8 deletions

diff --git a/src/global.c b/src/global.c
index b5239ad81..10c368f72 100644
--- a/src/global.c
+++ b/src/global.c
@@ -37,7 +37,7 @@ const unsigned char sqlite3UpperToLower[] = {
     198,199,200,201,202,203,204,205,206,207,208,209,210,211,212,213,214,215,
     216,217,218,219,220,221,222,223,224,225,226,227,228,229,230,231,232,233,
     234,235,236,237,238,239,240,241,242,243,244,245,246,247,248,249,250,251,
-    252,253,254,255
+    252,253,254,255,
 #endif
 #ifdef SQLITE_EBCDIC
       0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14, 15, /* 0x */
@@ -57,7 +57,35 @@ const unsigned char sqlite3UpperToLower[] = {
     224,225,162,163,164,165,166,167,168,169,234,235,236,237,238,239, /* Ex */
     240,241,242,243,244,245,246,247,248,249,250,251,252,253,254,255, /* Fx */
 #endif
+/* All of the upper-to-lower conversion data is above.  The following
+** 18 integers are completely unrelated.  They are appended to the
+** sqlite3UpperToLower[] array to avoid UBSAN warnings.  Here's what is
+** going on:
+**
+** The SQL comparison operators (<>, =, >, <=, <, and >=) are implemented
+** by invoking sqlite3MemCompare(A,B) which compares values A and B and
+** returns negative, zero, or positive if A is less then, equal to, or
+** greater than B, respectively.  Then the true false results is found by
+** consulting sqlite3aLTb[opcode], sqlite3aEQb[opcode], or 
+** sqlite3aGTb[opcode] depending on whether the result of compare(A,B)
+** is negative, zero, or positive, where opcode is the specific opcode.
+** The only works because the comparison opcodes are consecutive and in
+** this order: NE EQ GT LE LT GE.  Various assert()s throughout the code
+** ensure that is the case.
+**
+** These elements must be appended to another array.  Otherwise the
+** index (here shown as [256-OP_Ne]) would be out-of-bounds and thus
+** be undefined behavior.  That's goofy, but the C-standards people thought
+** it was a good idea, so here we are.
+*/
+/* NE  EQ  GT  LE  LT  GE  */
+   1,  0,  0,  1,  1,  0,  /* aLTb[]: Use when compare(A,B) less than zero */
+   0,  1,  0,  1,  0,  1,  /* aEQb[]: Use when compare(A,B) equals zero */
+   1,  0,  1,  0,  0,  1   /* aGTb[]: Use when compare(A,B) greater than zero*/
 };
+const unsigned char *sqlite3aLTb = &sqlite3UpperToLower[256-OP_Ne];
+const unsigned char *sqlite3aEQb = &sqlite3UpperToLower[256+6-OP_Ne];
+const unsigned char *sqlite3aGTb = &sqlite3UpperToLower[256+12-OP_Ne];
 
 /*
 ** The following 256 byte lookup table is used to support SQLites built-in
diff --git a/src/sqliteInt.h b/src/sqliteInt.h
index 0822a6c3c..cd2e9a2e2 100644
--- a/src/sqliteInt.h
+++ b/src/sqliteInt.h
@@ -4739,6 +4739,9 @@ void sqlite3ValueApplyAffinity(sqlite3_value *, u8, u8);
 extern const unsigned char sqlite3OpcodeProperty[];
 extern const char sqlite3StrBINARY[];
 extern const unsigned char sqlite3UpperToLower[];
+extern const unsigned char *sqlite3aLTb;
+extern const unsigned char *sqlite3aEQb;
+extern const unsigned char *sqlite3aGTb;
 extern const unsigned char sqlite3CtypeMap[];
 extern SQLITE_WSD struct Sqlite3Config sqlite3Config;
 extern FuncDefHash sqlite3BuiltinFunctions;
diff --git a/src/vdbe.c b/src/vdbe.c
index 080c7eaf8..0026ed377 100644
--- a/src/vdbe.c
+++ b/src/vdbe.c
@@ -2111,15 +2111,12 @@ compare_op:
   ** order:  NE, EQ, GT, LE, LT, GE */
   assert( OP_Eq==OP_Ne+1 ); assert( OP_Gt==OP_Ne+2 ); assert( OP_Le==OP_Ne+3 );
   assert( OP_Lt==OP_Ne+4 ); assert( OP_Ge==OP_Ne+5 );
-  if( res<0 ){                        /* ne, eq, gt, le, lt, ge */
-    static const unsigned char aLTb[] = { 1,  0,  0,  1,  1,  0 };
-    res2 = aLTb[pOp->opcode - OP_Ne];
+  if( res<0 ){
+    res2 = sqlite3aLTb[pOp->opcode];
   }else if( res==0 ){
-    static const unsigned char aEQb[] = { 0,  1,  0,  1,  0,  1 };
-    res2 = aEQb[pOp->opcode - OP_Ne];
+    res2 = sqlite3aEQb[pOp->opcode];
   }else{
-    static const unsigned char aGTb[] = { 1,  0,  1,  0,  0,  1 };
-    res2 = aGTb[pOp->opcode - OP_Ne];
+    res2 = sqlite3aGTb[pOp->opcode];
   }
 
   /* Undo any changes made by applyAffinity() to the input registers. */