[CodeGen][Tablegen] Fix uninitialized var and shift overflow. (#84896)

Fix uninitialized var and shift overflow.

Author: mahesh-attarde

llvm/include/llvm/CodeGen/AccelTable.h

@@ -353,7 +353,7 @@ class DebugNamesAbbrev : public FoldingSetNode {
     dwarf::Index Index;
     dwarf::Form Form;
   };
-  DebugNamesAbbrev(uint32_t DieTag) : DieTag(DieTag) {}
+  DebugNamesAbbrev(uint32_t DieTag) : DieTag(DieTag), Number(0) {}
   /// Add attribute encoding to an abbreviation.
   void addAttribute(const DebugNamesAbbrev::AttributeEncoding &Attr) {
     AttrVect.push_back(Attr);

llvm/lib/CodeGen/AsmPrinter/AccelTable.cpp

@@ -369,7 +369,8 @@ void AppleAccelTableWriter::emit() const {
 DWARF5AccelTableData::DWARF5AccelTableData(const DIE &Die,
                                            const uint32_t UnitID,
                                            const bool IsTU)
-    : OffsetVal(&Die), DieTag(Die.getTag()), IsTU(IsTU), UnitID(UnitID) {}
+    : OffsetVal(&Die), DieTag(Die.getTag()), AbbrevNumber(0), IsTU(IsTU),
+      UnitID(UnitID) {}
 
 void Dwarf5AccelTableWriter::Header::emit(Dwarf5AccelTableWriter &Ctx) {
   assert(CompUnitCount > 0 && "Index must have at least one CU.");

llvm/utils/TableGen/DecoderEmitter.cpp

@@ -934,7 +934,7 @@ void DecoderEmitter::emitTable(formatted_raw_ostream &OS, DecoderTable &Table,
       unsigned Shift = 0;
       do {
         OS << ", " << (unsigned)*I;
-        Value += (*I & 0x7f) << Shift;
+        Value += ((uint64_t)(*I & 0x7f)) << Shift;
         Shift += 7;
       } while (*I++ >= 128);
       if (Value > 127) {
@@ -947,7 +947,7 @@ void DecoderEmitter::emitTable(formatted_raw_ostream &OS, DecoderTable &Table,
       Shift = 0;
       do {
         OS << ", " << (unsigned)*I;
-        Value += (*I & 0x7f) << Shift;
+        Value += ((uint64_t)(*I & 0x7f)) << Shift;
         Shift += 7;
       } while (*I++ >= 128);
       if (Value > 127) {