diff --git a/libunwind/src/DwarfParser.hpp b/libunwind/src/DwarfParser.hpp
--- a/libunwind/src/DwarfParser.hpp
+++ b/libunwind/src/DwarfParser.hpp
@@ -77,6 +77,7 @@
   };
   struct RegisterLocation {
     RegisterSavedWhere location;
+    bool initialStateSaved;
     int64_t value;
   };
   /// Information about a frame layout and registers saved determined
@@ -90,6 +91,38 @@
     bool              registersInOtherRegisters;
     bool              sameValueUsed;
     RegisterLocation  savedRegisters[kMaxRegisterNumber + 1];
+    // When saving registers, this data structure is lazily initialized.
+    PrologInfo(bool Initialize = true) {
+      if (Initialize)
+        memset(this, 0, sizeof(*this));
+    }
+    void checkSaveRegister(uint64_t reg, PrologInfo &initialState) {
+      if (!savedRegisters[reg].initialStateSaved) {
+        initialState.savedRegisters[reg] = savedRegisters[reg];
+        savedRegisters[reg].initialStateSaved = true;
+      }
+    }
+    void setRegister(uint64_t reg, RegisterSavedWhere newLocation,
+                     int64_t newValue, PrologInfo &initialState) {
+      checkSaveRegister(reg, initialState);
+      savedRegisters[reg].location = newLocation;
+      savedRegisters[reg].value = newValue;
+    }
+    void setRegisterLocation(uint64_t reg, RegisterSavedWhere newLocation,
+                             PrologInfo &initialState) {
+      checkSaveRegister(reg, initialState);
+      savedRegisters[reg].location = newLocation;
+    }
+    void setRegisterValue(uint64_t reg, int64_t newValue,
+                          PrologInfo &initialState) {
+      checkSaveRegister(reg, initialState);
+      savedRegisters[reg].value = newValue;
+    }
+    void restoreRegisterToInitialState(uint64_t reg, PrologInfo &initialState) {
+      if (savedRegisters[reg].initialStateSaved)
+        savedRegisters[reg] = initialState.savedRegisters[reg];
+      // else the register still holds its initial state
+    }
   };
 
   struct PrologInfoStackEntry {
@@ -355,8 +388,6 @@
                                          const FDE_Info &fdeInfo,
                                          const CIE_Info &cieInfo, pint_t upToPC,
                                          int arch, PrologInfo *results) {
-  // clear results
-  memset(results, '\0', sizeof(PrologInfo));
   PrologInfoStackEntry *rememberStack = NULL;
 
   // parse CIE then FDE instructions
@@ -390,7 +421,10 @@
                                       int arch, PrologInfo *results) {
   pint_t p = instructions;
   pint_t codeOffset = 0;
-  PrologInfo initialState = *results;
+  // initialState is lazily initialized as registers in results are
+  // modified. Take care to use PrologInfo accessor functions to avoid reading
+  // uninitialized data.
+  PrologInfo initialState(false);
 
   _LIBUNWIND_TRACE_DWARF("parseInstructions(instructions=0x%0" PRIx64 ")\n",
                          static_cast<uint64_t>(instructionsEnd));
@@ -443,8 +477,7 @@
                 "malformed DW_CFA_offset_extended DWARF unwind, reg too big");
         return false;
       }
-      results->savedRegisters[reg].location = kRegisterInCFA;
-      results->savedRegisters[reg].value = offset;
+      results->setRegister(reg, kRegisterInCFA, offset, initialState);
       _LIBUNWIND_TRACE_DWARF("DW_CFA_offset_extended(reg=%" PRIu64 ", "
                              "offset=%" PRId64 ")\n",
                              reg, offset);
@@ -456,7 +489,7 @@
             "malformed DW_CFA_restore_extended DWARF unwind, reg too big");
         return false;
       }
-      results->savedRegisters[reg] = initialState.savedRegisters[reg];
+      results->restoreRegisterToInitialState(reg, initialState);
       _LIBUNWIND_TRACE_DWARF("DW_CFA_restore_extended(reg=%" PRIu64 ")\n", reg);
       break;
     case DW_CFA_undefined:
@@ -466,7 +499,7 @@
                 "malformed DW_CFA_undefined DWARF unwind, reg too big");
         return false;
       }
-      results->savedRegisters[reg].location = kRegisterUnused;
+      results->setRegisterLocation(reg, kRegisterUnused, initialState);
       _LIBUNWIND_TRACE_DWARF("DW_CFA_undefined(reg=%" PRIu64 ")\n", reg);
       break;
     case DW_CFA_same_value:
@@ -480,7 +513,7 @@
       // "same value" means register was stored in frame, but its current
       // value has not changed, so no need to restore from frame.
       // We model this as if the register was never saved.
-      results->savedRegisters[reg].location = kRegisterUnused;
+      results->setRegisterLocation(reg, kRegisterUnused, initialState);
       // set flag to disable conversion to compact unwind
       results->sameValueUsed = true;
       _LIBUNWIND_TRACE_DWARF("DW_CFA_same_value(reg=%" PRIu64 ")\n", reg);
@@ -498,8 +531,8 @@
                 "malformed DW_CFA_register DWARF unwind, reg2 too big");
         return false;
       }
-      results->savedRegisters[reg].location = kRegisterInRegister;
-      results->savedRegisters[reg].value = (int64_t)reg2;
+      results->setRegister(reg, kRegisterInRegister, (int64_t)reg2,
+                           initialState);
       // set flag to disable conversion to compact unwind
       results->registersInOtherRegisters = true;
       _LIBUNWIND_TRACE_DWARF(
@@ -576,8 +609,8 @@
                 "malformed DW_CFA_expression DWARF unwind, reg too big");
         return false;
       }
-      results->savedRegisters[reg].location = kRegisterAtExpression;
-      results->savedRegisters[reg].value = (int64_t)p;
+      results->setRegister(reg, kRegisterAtExpression, (int64_t)p,
+                           initialState);
       length = addressSpace.getULEB128(p, instructionsEnd);
       assert(length < static_cast<pint_t>(~0) && "pointer overflow");
       p += static_cast<pint_t>(length);
@@ -595,8 +628,7 @@
       }
       offset =
           addressSpace.getSLEB128(p, instructionsEnd) * cieInfo.dataAlignFactor;
-      results->savedRegisters[reg].location = kRegisterInCFA;
-      results->savedRegisters[reg].value = offset;
+      results->setRegister(reg, kRegisterInCFA, offset, initialState);
       _LIBUNWIND_TRACE_DWARF("DW_CFA_offset_extended_sf(reg=%" PRIu64 ", "
                              "offset=%" PRId64 ")\n",
                              reg, offset);
@@ -634,8 +666,7 @@
       }
       offset = (int64_t)addressSpace.getULEB128(p, instructionsEnd)
                                                     * cieInfo.dataAlignFactor;
-      results->savedRegisters[reg].location = kRegisterOffsetFromCFA;
-      results->savedRegisters[reg].value = offset;
+      results->setRegister(reg, kRegisterOffsetFromCFA, offset, initialState);
       _LIBUNWIND_TRACE_DWARF("DW_CFA_val_offset(reg=%" PRIu64 ", "
                              "offset=%" PRId64 "\n",
                              reg, offset);
@@ -649,8 +680,7 @@
       }
       offset =
           addressSpace.getSLEB128(p, instructionsEnd) * cieInfo.dataAlignFactor;
-      results->savedRegisters[reg].location = kRegisterOffsetFromCFA;
-      results->savedRegisters[reg].value = offset;
+      results->setRegister(reg, kRegisterOffsetFromCFA, offset, initialState);
       _LIBUNWIND_TRACE_DWARF("DW_CFA_val_offset_sf(reg=%" PRIu64 ", "
                              "offset=%" PRId64 "\n",
                              reg, offset);
@@ -662,8 +692,8 @@
                 "malformed DW_CFA_val_expression DWARF unwind, reg too big");
         return false;
       }
-      results->savedRegisters[reg].location = kRegisterIsExpression;
-      results->savedRegisters[reg].value = (int64_t)p;
+      results->setRegister(reg, kRegisterIsExpression, (int64_t)p,
+                           initialState);
       length = addressSpace.getULEB128(p, instructionsEnd);
       assert(length < static_cast<pint_t>(~0) && "pointer overflow");
       p += static_cast<pint_t>(length);
@@ -685,8 +715,7 @@
       }
       offset = (int64_t)addressSpace.getULEB128(p, instructionsEnd)
                                                     * cieInfo.dataAlignFactor;
-      results->savedRegisters[reg].location = kRegisterInCFA;
-      results->savedRegisters[reg].value = -offset;
+      results->setRegister(reg, kRegisterInCFA, -offset, initialState);
       _LIBUNWIND_TRACE_DWARF(
           "DW_CFA_GNU_negative_offset_extended(%" PRId64 ")\n", offset);
       break;
@@ -699,25 +728,27 @@
     case DW_CFA_AARCH64_negate_ra_state:
       switch (arch) {
 #if defined(_LIBUNWIND_TARGET_AARCH64)
-      case REGISTERS_ARM64:
-        results->savedRegisters[UNW_ARM64_RA_SIGN_STATE].value ^= 0x1;
-        _LIBUNWIND_TRACE_DWARF("DW_CFA_AARCH64_negate_ra_state\n");
-        break;
+        case REGISTERS_ARM64: {
+          int64_t value =
+              results->savedRegisters[UNW_ARM64_RA_SIGN_STATE].value ^ 0x1;
+          results->setRegisterValue(UNW_ARM64_RA_SIGN_STATE, value, initialState);
+          _LIBUNWIND_TRACE_DWARF("DW_CFA_AARCH64_negate_ra_state\n");
+        } break;
 #endif
+
 #if defined(_LIBUNWIND_TARGET_SPARC)
       // case DW_CFA_GNU_window_save:
       case REGISTERS_SPARC:
         _LIBUNWIND_TRACE_DWARF("DW_CFA_GNU_window_save()\n");
         for (reg = UNW_SPARC_O0; reg <= UNW_SPARC_O7; reg++) {
-          results->savedRegisters[reg].location = kRegisterInRegister;
-          results->savedRegisters[reg].value =
-              ((int64_t)reg - UNW_SPARC_O0) + UNW_SPARC_I0;
+          results->setRegister(reg, kRegisterInRegister,
+                               ((int64_t)reg - UNW_SPARC_O0) + UNW_SPARC_I0,
+                               initialState);
         }
 
         for (reg = UNW_SPARC_L0; reg <= UNW_SPARC_I7; reg++) {
-          results->savedRegisters[reg].location = kRegisterInCFA;
-          results->savedRegisters[reg].value =
-              ((int64_t)reg - UNW_SPARC_L0) * 4;
+          results->setRegister(reg, kRegisterInCFA,
+                               ((int64_t)reg - UNW_SPARC_L0) * 4, initialState);
         }
         break;
 #endif
@@ -740,8 +771,7 @@
         }
         offset = (int64_t)addressSpace.getULEB128(p, instructionsEnd)
                                                     * cieInfo.dataAlignFactor;
-        results->savedRegisters[reg].location = kRegisterInCFA;
-        results->savedRegisters[reg].value = offset;
+        results->setRegister(reg, kRegisterInCFA, offset, initialState);
         _LIBUNWIND_TRACE_DWARF("DW_CFA_offset(reg=%d, offset=%" PRId64 ")\n",
                                operand, offset);
         break;
@@ -758,7 +788,7 @@
                   reg);
           return false;
         }
-        results->savedRegisters[reg] = initialState.savedRegisters[reg];
+        results->restoreRegisterToInitialState(reg, initialState);
         _LIBUNWIND_TRACE_DWARF("DW_CFA_restore(reg=%" PRIu64 ")\n",
                                static_cast<uint64_t>(operand));
         break;