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
@@ -1135,6 +1135,9 @@
   virtual const BitVector &getAliases(MCPhysReg Reg,
                                       bool OnlySmaller = false) const;
 
+  /// Initialize aliases tables.
+  virtual void initAliases();
+
   /// Change \p Regs setting all registers used to pass parameters according
   /// to the host abi. Do nothing if not implemented.
   virtual BitVector getRegsUsedAsParams() const {
@@ -1904,6 +1907,11 @@
     llvm_unreachable("not implemented");
     return BlocksVectorTy();
   }
+
+  // AliasMap caches a mapping of registers to the set of registers that
+  // alias (are sub or superregs of itself, including itself).
+  std::vector<BitVector> AliasMap;
+  std::vector<BitVector> SmallerAliasMap;
 };
 
 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
@@ -441,17 +441,13 @@
 
 const BitVector &MCPlusBuilder::getAliases(MCPhysReg Reg,
                                            bool OnlySmaller) const {
-  // AliasMap caches a mapping of registers to the set of registers that
-  // alias (are sub or superregs of itself, including itself).
-  static std::vector<BitVector> AliasMap;
-  static std::vector<BitVector> SmallerAliasMap;
-
-  if (AliasMap.size() > 0) {
-    if (OnlySmaller)
-      return SmallerAliasMap[Reg];
-    return AliasMap[Reg];
-  }
+  if (OnlySmaller)
+    return SmallerAliasMap[Reg];
+  return AliasMap[Reg];
+}
 
+void MCPlusBuilder::initAliases() {
+  assert(AliasMap.size() == 0 && SmallerAliasMap.size() == 0);
   // Build alias map
   for (MCPhysReg I = 0, E = RegInfo->getNumRegs(); I != E; ++I) {
     BitVector BV(RegInfo->getNumRegs(), false);
@@ -492,10 +488,6 @@
       dbgs() << "\n";
     }
   });
-
-  if (OnlySmaller)
-    return SmallerAliasMap[Reg];
-  return AliasMap[Reg];
 }
 
 uint8_t MCPlusBuilder::getRegSize(MCPhysReg Reg) const {
diff --git a/bolt/lib/Target/AArch64/AArch64MCPlusBuilder.cpp b/bolt/lib/Target/AArch64/AArch64MCPlusBuilder.cpp
--- a/bolt/lib/Target/AArch64/AArch64MCPlusBuilder.cpp
+++ b/bolt/lib/Target/AArch64/AArch64MCPlusBuilder.cpp
@@ -1149,7 +1149,9 @@
 MCPlusBuilder *createAArch64MCPlusBuilder(const MCInstrAnalysis *Analysis,
                                           const MCInstrInfo *Info,
                                           const MCRegisterInfo *RegInfo) {
-  return new AArch64MCPlusBuilder(Analysis, Info, RegInfo);
+  MCPlusBuilder *MIB = new AArch64MCPlusBuilder(Analysis, Info, RegInfo);
+  MIB->initAliases();
+  return MIB;
 }
 
 } // namespace bolt
diff --git a/bolt/lib/Target/X86/X86MCPlusBuilder.cpp b/bolt/lib/Target/X86/X86MCPlusBuilder.cpp
--- a/bolt/lib/Target/X86/X86MCPlusBuilder.cpp
+++ b/bolt/lib/Target/X86/X86MCPlusBuilder.cpp
@@ -3719,7 +3719,9 @@
 MCPlusBuilder *createX86MCPlusBuilder(const MCInstrAnalysis *Analysis,
                                       const MCInstrInfo *Info,
                                       const MCRegisterInfo *RegInfo) {
-  return new X86MCPlusBuilder(Analysis, Info, RegInfo);
+  MCPlusBuilder *MIB = new X86MCPlusBuilder(Analysis, Info, RegInfo);
+  MIB->initAliases();
+  return MIB;
 }
 
 } // namespace bolt