[disassembler] Do not search for literal loads inside constant pools

We try and match literal load instructions in order to print a
relocation info comment. However, we could be doing it while we're
decoding a constant pool. This would cause a DCHECK to fire on Arm64
with full pointers.

Change-Id: I82a523dc5c033f86f41467db75e43419ab87d5ca
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2756532Reviewed-by: Santiago Aboy Solanes <solanes@chromium.org>
Commit-Queue: Pierre Langlois <pierre.langlois@arm.com>
Cr-Commit-Position: refs/heads/master@{#73429}

src/diagnostics/disassembler.cc

@@ -301,7 +301,8 @@ static int DecodeIt(Isolate* isolate, ExternalReferenceEncoder* ref_encoder,
   while (pc < end) {
     // First decode instruction so that we know its length.
     byte* prev_pc = pc;
-    if (constants > 0) {
+    bool decoding_constant_pool = constants > 0;
+    if (decoding_constant_pool) {
       SNPrintF(
           decode_buffer, "%08x       constant",
           base::ReadUnalignedValue<int32_t>(reinterpret_cast<Address>(pc)));
@@ -391,7 +392,11 @@ static int DecodeIt(Isolate* isolate, ExternalReferenceEncoder* ref_encoder,
     // If this is a constant pool load and we haven't found any RelocInfo
     // already, check if we can find some RelocInfo for the target address in
     // the constant pool.
-    if (pcs.empty() && !code.is_null()) {
+    // Make sure we're also not currently in the middle of decoding a constant
+    // pool itself, rather than a contant pool load. Since it can store any
+    // bytes, a constant could accidentally match with the bit-pattern checked
+    // by IsInConstantPool() below.
+    if (pcs.empty() && !code.is_null() && !decoding_constant_pool) {
       RelocInfo dummy_rinfo(reinterpret_cast<Address>(prev_pc), RelocInfo::NONE,
                             0, Code());
       if (dummy_rinfo.IsInConstantPool()) {