Add additional effiency checks to sanity checker

Author: sipa

src/util/asmap.cpp

@@ -126,11 +126,14 @@ bool SanityCheckASMap(const std::vector<bool>& asmap, int bits)
     std::vector<bool>::const_iterator pos = begin;
     std::vector<std::pair<uint32_t, int>> jumps; // All future positions we may jump to (bit offset in asmap -> bits to consume left)
     jumps.reserve(bits);
+    Instruction prevopcode = Instruction::JUMP;
+    bool had_incomplete_match = false;
     while (pos != endpos) {
         uint32_t offset = pos - begin;
         if (!jumps.empty() && offset >= jumps.back().first) return false; // There was a jump into the middle of the previous instruction
         Instruction opcode = DecodeType(pos, endpos);
         if (opcode == Instruction::RETURN) {
+            if (prevopcode == Instruction::DEFAULT) return false; // There should not be any RETURN immediately after a DEFAULT (could be combined into just RETURN)
             uint32_t asn = DecodeASN(pos, endpos);
             if (asn == INVALID) return false; // ASN straddles EOF
             if (jumps.empty()) {
@@ -147,6 +150,7 @@ bool SanityCheckASMap(const std::vector<bool>& asmap, int bits)
                 if (offset != jumps.back().first) return false; // Unreachable code
                 bits = jumps.back().second; // Restore the number of bits we would have had left after this jump
                 jumps.pop_back();
+                prevopcode = Instruction::JUMP;
             }
         } else if (opcode == Instruction::JUMP) {
             uint32_t jump = DecodeJump(pos, endpos);
@@ -157,15 +161,22 @@ bool SanityCheckASMap(const std::vector<bool>& asmap, int bits)
             uint32_t jump_offset = pos - begin + jump;
             if (!jumps.empty() && jump_offset >= jumps.back().first) return false; // Intersecting jumps
             jumps.emplace_back(jump_offset, bits);
+            prevopcode = Instruction::JUMP;
         } else if (opcode == Instruction::MATCH) {
             uint32_t match = DecodeMatch(pos, endpos);
             if (match == INVALID) return false; // Match bits straddle EOF
             int matchlen = CountBits(match) - 1;
+            if (prevopcode != Instruction::MATCH) had_incomplete_match = false;
+            if (matchlen < 8 && had_incomplete_match) return false; // Within a sequence of matches only at most one should be incomplete
+            had_incomplete_match = (matchlen < 8);
             if (bits < matchlen) return false; // Consuming bits past the end of the input
             bits -= matchlen;
+            prevopcode = Instruction::MATCH;
         } else if (opcode == Instruction::DEFAULT) {
+            if (prevopcode == Instruction::DEFAULT) return false; // There should not be two successive DEFAULTs (they could be combined into one)
             uint32_t asn = DecodeASN(pos, endpos);
             if (asn == INVALID) return false; // ASN straddles EOF
+            prevopcode = Instruction::DEFAULT;
         } else {
             return false; // Instruction straddles EOF
         }