diff --git a/bolt/include/bolt/Core/MCPlusBuilder.h b/bolt/include/bolt/Core/MCPlusBuilder.h
--- a/bolt/include/bolt/Core/MCPlusBuilder.h
+++ b/bolt/include/bolt/Core/MCPlusBuilder.h
@@ -310,6 +310,7 @@
     MaxAllocatorId++;
     // Build alias map
     initAliases();
+    initSizeMap();
   }
 
   /// Create and return target-specific MC symbolizer for the \p Function.
@@ -1193,7 +1194,10 @@
                                       bool OnlySmaller = false) const;
 
   /// Initialize aliases tables.
-  virtual void initAliases();
+  void initAliases();
+
+  /// Initialize register size table.
+  void initSizeMap();
 
   /// Change \p Regs setting all registers used to pass parameters according
   /// to the host abi. Do nothing if not implemented.
@@ -1236,7 +1240,7 @@
   }
 
   /// Return the register width in bytes (1, 2, 4 or 8)
-  virtual uint8_t getRegSize(MCPhysReg Reg) const;
+  uint8_t getRegSize(MCPhysReg Reg) const { return SizeMap[Reg]; }
 
   /// For aliased registers, return an alias of \p Reg that has the width of
   /// \p Size bytes
@@ -1986,6 +1990,8 @@
   // alias (are sub or superregs of itself, including itself).
   std::vector<BitVector> AliasMap;
   std::vector<BitVector> SmallerAliasMap;
+  // SizeMap caches a mapping of registers to their sizes.
+  std::vector<uint8_t> SizeMap;
 };
 
 MCPlusBuilder *createX86MCPlusBuilder(const MCInstrAnalysis *,
diff --git a/bolt/lib/Core/MCPlusBuilder.cpp b/bolt/lib/Core/MCPlusBuilder.cpp
--- a/bolt/lib/Core/MCPlusBuilder.cpp
+++ b/bolt/lib/Core/MCPlusBuilder.cpp
@@ -483,22 +483,12 @@
   });
 }
 
-uint8_t MCPlusBuilder::getRegSize(MCPhysReg Reg) const {
-  // SizeMap caches a mapping of registers to their sizes
-  static std::vector<uint8_t> SizeMap;
-
-  if (SizeMap.size() > 0) {
-    return SizeMap[Reg];
-  }
-  SizeMap = std::vector<uint8_t>(RegInfo->getNumRegs());
+void MCPlusBuilder::initSizeMap() {
+  SizeMap.resize(RegInfo->getNumRegs());
   // Build size map
-  for (auto I = RegInfo->regclass_begin(), E = RegInfo->regclass_end(); I != E;
-       ++I) {
-    for (MCPhysReg Reg : *I)
-      SizeMap[Reg] = I->getSizeInBits() / 8;
-  }
-
-  return SizeMap[Reg];
+  for (auto RC : RegInfo->regclasses())
+    for (MCPhysReg Reg : RC)
+      SizeMap[Reg] = RC.getSizeInBits() / 8;
 }
 
 bool MCPlusBuilder::setOperandToSymbolRef(MCInst &Inst, int OpNum,