Add folding and simplication for OP_ECLASS

Fixes #537

.github/workflows/dev.yml

@@ -68,7 +68,7 @@ jobs:
 
       - name: Test (main test script)
         run: |
-          ulimit -S -s 32768 # Raise stack limit; ASAN with -O0 is very stack-hungry
+          ulimit -S -s 49152 # Raise stack limit; ASAN with -O0 is very stack-hungry
           ./RunTest
 
       - name: Test (JIT test program)

HACKING

@@ -633,6 +633,41 @@ When XCL_NOT is set, the bit map, if present, contains bits for characters that
 are allowed (exactly as for OP_NCLASS), but the list of items that follow it
 specifies characters and properties that are not allowed.
 
+The meaning of the bitmap indicated by XCL_MAP is that, if one is present, then
+it fully describes which code points < 256 match the class (without needing to
+invert the check according to XCL_NOT); the other items in the OP_XCLASS need
+not be consulted. However, if a bitmap is not present, then code points < 256
+may still match, so the other items in the OP_XCLASS must be consulted.
+
+For classes containing logical expressions, such as "[\p{Greek} && \p{Lu}]" for
+"uppercase Greek letters", OP_ECLASS is used. The expression is encoded as a
+a stack-based series of operands and operators, in Reverse Polish Notation.
+Like an OP_XCLASS, the OP_ECLASS is first followed by a LINK_SIZE value
+containing the total length of the opcode and its data. That is followed by a
+code containing flags: currently just ECL_MAP indicating that a bit map is
+present. There follows the bit map, if ECL_MAP is set. Finally a sequence of
+items that are either an operand or operator. Each item starts with a single
+code unit containing its type:
+
+  ECL_AND       AND; no additional data
+  ECL_OR        OR; no additional data
+  ECL_XOR       XOR; no additional data
+  ECL_NOT       NOT; no additional data
+  ECL_XCLASS    The additional data which follows ECL_XCLASS is the same as for
+                an OP_XCLASS, except that this data is preceded by ECL_XCLASS
+                rather than OP_XCLASS.
+
+Additionally, there are two intermediate values used during compilation, but
+these are folded away during generation of the opcode, and so never appear
+inside an OP_ECLASS at match time. They are:
+
+  ECL_ANY       match all characters; no additional data
+  ECL_NONE      match no characters; no additional data
+
+The meaning of the bitmap indicated by ECL_MAP is different to that of XCL_MAP
+for OP_XCLASS, in one way. The ECL_MAP bitmap is present whenever any code
+points < 256 match the class.
+
 
 Back references
 ---------------

src/pcre2_auto_possess.c

@@ -480,13 +480,13 @@ switch(c)
 
   case OP_NCLASS:
   case OP_CLASS:
+#ifdef SUPPORT_WIDE_CHARS
   case OP_XCLASS:
   case OP_ECLASS:
-  /* TODO: [EC] https://github.com/PCRE2Project/pcre2/issues/537
-  Add back the "ifdef SUPPORT_WIDE_CHARS" once we stop emitting ECLASS for this case. */
   if (c == OP_XCLASS || c == OP_ECLASS)
     end = code + GET(code, 0) - 1;
   else
+#endif
     end = code + 32 / sizeof(PCRE2_UCHAR);
   class_end = end;
 
@@ -1118,17 +1118,15 @@ for(;;)
           list_ptr[2] + LINK_SIZE, (const uint8_t*)cb->start_code, utf))
         return FALSE;
       break;
-#endif
 
-      /* TODO: [EC] https://github.com/PCRE2Project/pcre2/issues/537
-      Enclose in "ifdef SUPPORT_WIDE_CHARS" once we stop emitting ECLASS for this case. */
       case OP_ECLASS:
       if (PRIV(eclass)(chr,
           (list_ptr == list ? code : base_end) - list_ptr[2] + LINK_SIZE,
           (list_ptr == list ? code : base_end) - list_ptr[3],
           (const uint8_t*)cb->start_code, utf))
         return FALSE;
       break;
+#endif /* SUPPORT_WIDE_CHARS */
 
       default:
       return FALSE;
@@ -1236,13 +1234,17 @@ for (;;)
       }
     c = *code;
     }
-  else if (c == OP_CLASS || c == OP_NCLASS || c == OP_XCLASS || c == OP_ECLASS)
+  else if (c == OP_CLASS || c == OP_NCLASS
+#ifdef SUPPORT_WIDE_CHARS
+           || c == OP_XCLASS || c == OP_ECLASS
+#endif
+           )
     {
-    /* TODO: [EC] https://github.com/PCRE2Project/pcre2/issues/537
-    Add back the "ifdef SUPPORT_WIDE_CHARS" once we stop emitting ECLASS for this case. */
+#ifdef SUPPORT_WIDE_CHARS
     if (c == OP_XCLASS || c == OP_ECLASS)
       repeat_opcode = code + GET(code, 1);
     else
+#endif
       repeat_opcode = code + 1 + (32 / sizeof(PCRE2_UCHAR));
 
     c = *repeat_opcode;
@@ -1315,12 +1317,12 @@ for (;;)
     code += GET(code, 1 + 2*LINK_SIZE);
     break;
 
-    /* TODO: [EC] https://github.com/PCRE2Project/pcre2/issues/537
-    Add back the "ifdef SUPPORT_WIDE_CHARS" once we stop emitting ECLASS for this case. */
-    case OP_ECLASS:
+#ifdef SUPPORT_WIDE_CHARS
     case OP_XCLASS:
+    case OP_ECLASS:
     code += GET(code, 1);
     break;
+#endif
 
     case OP_MARK:
     case OP_COMMIT_ARG: