[X86][NFC] Use single table for EVEX compression

This patch is to address my review comments in #77065 to simplify the
implemention of EVEX2Legacy compression.

Author: KanRobert

llvm/lib/Target/X86/X86CompressEVEX.cpp

@@ -224,16 +224,7 @@ static bool performCustomAdjustments(MachineInstr &MI, unsigned NewOpc) {
   return true;
 }
 
-// For EVEX instructions that can be encoded using VEX encoding
-// replace them by the VEX encoding in order to reduce size.
-static bool CompressEvexToVexImpl(MachineInstr &MI, const X86Subtarget &ST) {
-  // VEX format.
-  // # of bytes: 0,2,3  1      1      0,1   0,1,2,4  0,1
-  //  [Prefixes] [VEX]  OPCODE ModR/M [SIB] [DISP]  [IMM]
-  //
-  // EVEX format.
-  //  # of bytes: 4    1      1      1      4       / 1         1
-  //  [Prefixes]  EVEX Opcode ModR/M [SIB] [Disp32] / [Disp8*N] [Immediate]
+static bool CompressEVEXImpl(MachineInstr &MI, const X86Subtarget &ST) {
   const MCInstrDesc &Desc = MI.getDesc();
 
   // Check for EVEX instructions only.
@@ -251,10 +242,7 @@ static bool CompressEvexToVexImpl(MachineInstr &MI, const X86Subtarget &ST) {
   if (Desc.TSFlags & X86II::EVEX_L2)
     return false;
 
-  // Use the VEX.L bit to select the 128 or 256-bit table.
-  ArrayRef<X86CompressEVEXTableEntry> Table =
-      (Desc.TSFlags & X86II::VEX_L) ? ArrayRef(X86EvexToVex256CompressTable)
-                                    : ArrayRef(X86EvexToVex128CompressTable);
+  ArrayRef<X86CompressEVEXTableEntry> Table = ArrayRef(X86CompressEVEXTable);
 
   unsigned Opc = MI.getOpcode();
   const auto *I = llvm::lower_bound(Table, Opc);
@@ -278,10 +266,8 @@ bool CompressEVEXPass::runOnMachineFunction(MachineFunction &MF) {
   // Make sure the tables are sorted.
   static std::atomic<bool> TableChecked(false);
   if (!TableChecked.load(std::memory_order_relaxed)) {
-    assert(llvm::is_sorted(X86EvexToVex128CompressTable) &&
-           "X86EvexToVex128CompressTable is not sorted!");
-    assert(llvm::is_sorted(X86EvexToVex256CompressTable) &&
-           "X86EvexToVex256CompressTable is not sorted!");
+    assert(llvm::is_sorted(X86CompressEVEXTable) &&
+           "X86CompressEVEXTable is not sorted!");
     TableChecked.store(true, std::memory_order_relaxed);
   }
 #endif
@@ -291,12 +277,10 @@ bool CompressEVEXPass::runOnMachineFunction(MachineFunction &MF) {
 
   bool Changed = false;
 
-  /// Go over all basic blocks in function and replace
-  /// EVEX encoded instrs by VEX encoding when possible.
   for (MachineBasicBlock &MBB : MF) {
     // Traverse the basic block.
     for (MachineInstr &MI : MBB)
-      Changed |= CompressEvexToVexImpl(MI, ST);
+      Changed |= CompressEVEXImpl(MI, ST);
   }
 
   return Changed;

llvm/utils/TableGen/X86CompressEVEXTablesEmitter.cpp

@@ -47,9 +47,7 @@ class X86CompressEVEXTablesEmitter {
   typedef std::pair<const CodeGenInstruction *, const CodeGenInstruction *>
       Entry;
 
-  // Represent both compress tables
-  std::vector<Entry> EVEX2VEX128;
-  std::vector<Entry> EVEX2VEX256;
+  std::vector<Entry> Table;
 
 public:
   X86CompressEVEXTablesEmitter(RecordKeeper &R) : Records(R), Target(R) {}
@@ -64,20 +62,13 @@ class X86CompressEVEXTablesEmitter {
 
 void X86CompressEVEXTablesEmitter::printTable(const std::vector<Entry> &Table,
                                               raw_ostream &OS) {
-  StringRef Size = (Table == EVEX2VEX128) ? "128" : "256";
 
-  OS << "// X86 EVEX encoded instructions that have a VEX " << Size
-     << " encoding\n"
-     << "// (table format: <EVEX opcode, VEX-" << Size << " opcode>).\n"
-     << "static const X86CompressEVEXTableEntry X86EvexToVex" << Size
-     << "CompressTable[] = {\n"
-     << "  // EVEX scalar with corresponding VEX.\n";
+  OS << "static const X86CompressEVEXTableEntry X86CompressEVEXTable[] = { \n";
 
   // Print all entries added to the table
-  for (const auto &Pair : Table) {
+  for (const auto &Pair : Table)
     OS << "  { X86::" << Pair.first->TheDef->getName()
        << ", X86::" << Pair.second->TheDef->getName() << " },\n";
-  }
 
   OS << "};\n\n";
 }
@@ -175,33 +166,27 @@ void X86CompressEVEXTablesEmitter::run(raw_ostream &OS) {
     const Record *Rec = Inst->TheDef;
     uint64_t Opcode =
         getValueFromBitsInit(Inst->TheDef->getValueAsBitsInit("Opcode"));
-    const CodeGenInstruction *VEXInst = nullptr;
+    const CodeGenInstruction *NewInst = nullptr;
     if (ManualMap.find(Rec->getName()) != ManualMap.end()) {
       Record *NewRec = Records.getDef(ManualMap.at(Rec->getName()));
       assert(NewRec && "Instruction not found!");
-      VEXInst = &Target.getInstruction(NewRec);
+      NewInst = &Target.getInstruction(NewRec);
     } else {
-      // For each EVEX instruction look for a VEX match in the appropriate
+      // For each pre-compression instruction look for a match in the appropriate
       // vector (instructions with the same opcode) using function object
       // IsMatch.
       auto Match = llvm::find_if(CompressedInsts[Opcode], IsMatch(Inst));
       if (Match != CompressedInsts[Opcode].end())
-        VEXInst = *Match;
+        NewInst = *Match;
     }
 
-    if (!VEXInst)
+    if (!NewInst)
       continue;
 
-    // In case a match is found add new entry to the appropriate table
-    if (Rec->getValueAsBit("hasVEX_L"))
-      EVEX2VEX256.push_back(std::make_pair(Inst, VEXInst)); // {0,1}
-    else
-      EVEX2VEX128.push_back(std::make_pair(Inst, VEXInst)); // {0,0}
+    Table.push_back(std::make_pair(Inst, NewInst));
   }
 
-  // Print both tables
-  printTable(EVEX2VEX128, OS);
-  printTable(EVEX2VEX256, OS);
+  printTable(Table, OS);
 }
 } // namespace