[BOLT][NFC] Fix MCPlusBuilder::getAliases caching behavior

Caching behavior of `getAliases` causes a failure in unit tests where two
MCPlusBuilder objects are created corresponding to AArch64 and X86:
the alias cache is created for AArch64 but then used for X86.

https://lab.llvm.org/staging/#/builders/211/builds/126

The issue only affects unit tests as we only construct one MCPlusBuilder
for ELF binary.

Resolve the issue by moving alias bitvectors to MCPlusBuilder object.

Reviewed By: yota9

Differential Revision: https://reviews.llvm.org/D124942

Author: aaupov

bolt/include/bolt/Core/MCPlusBuilder.h

@@ -282,6 +282,8 @@ class MCPlusBuilder {
     // Initialize the default annotation allocator with id 0
     AnnotationAllocators.emplace(0, AnnotationAllocator());
     MaxAllocatorId++;
+    // Build alias map
+    initAliases();
   }
 
   /// Initialize a new annotation allocator and return its id
@@ -1135,6 +1137,9 @@ class MCPlusBuilder {
   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 +1909,11 @@ class MCPlusBuilder {
     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 *,

bolt/lib/Core/MCPlusBuilder.cpp

@@ -441,17 +441,13 @@ bool MCPlusBuilder::hasUseOfPhysReg(const MCInst &MI, unsigned Reg) const {
 
 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 @@ const BitVector &MCPlusBuilder::getAliases(MCPhysReg Reg,
       dbgs() << "\n";
     }
   });
-
-  if (OnlySmaller)
-    return SmallerAliasMap[Reg];
-  return AliasMap[Reg];
 }
 
 uint8_t MCPlusBuilder::getRegSize(MCPhysReg Reg) const {