[RISCV] Tablegen-driven Instruction Compression.

Summary:

    This patch implements a tablegen-driven Instruction Compression
    mechanism for generating RISCV compressed instructions
    (C Extension) from the expanded instruction form.

    This tablegen backend processes CompressPat declarations in a
    td file and generates all the compile-time and runtime checks
    required to validate the declarations, validate the input
    operands and generate correct instructions.

    The checks include validating register operands, immediate
    operands, fixed register operands and fixed immediate operands.

    Example:
      class CompressPat<dag input, dag output> {
        dag Input  = input;
        dag Output    = output;
        list<Predicate> Predicates = [];
      }

      let Predicates = [HasStdExtC] in {
      def : CompressPat<(ADD GPRNoX0:$rs1, GPRNoX0:$rs1, GPRNoX0:$rs2),
                        (C_ADD GPRNoX0:$rs1, GPRNoX0:$rs2)>;
      }

    The result is an auto-generated header file
    'RISCVGenCompressEmitter.inc' which exports two functions for
    compressing/uncompressing MCInst instructions, plus
    some helper functions:

      bool compressInst(MCInst& OutInst, const MCInst &MI,
                        const MCSubtargetInfo &STI,
                        MCContext &Context);

      bool uncompressInst(MCInst& OutInst, const MCInst &MI,
                          const MCRegisterInfo &MRI,
                          const MCSubtargetInfo &STI);

    The clients that include this auto-generated header file and
    invoke these functions can compress an instruction before emitting
    it, in the target-specific ASM or ELF streamer, or can uncompress
    an instruction before printing it, when the expanded instruction
    format aliases is favored.

    The following clients were added to implement compression\uncompression
    for RISCV:

    1) RISCVAsmParser::MatchAndEmitInstruction:
       Inserted a call to compressInst() to compresses instructions
       parsed by llvm-mc coming from an ASM input.
    2) RISCVAsmPrinter::EmitInstruction:
       Inserted a call to compressInst() to compress instructions that
       were lowered from Machine Instructions (MachineInstr).
    3) RVInstPrinter::printInst:
       Inserted a call to uncompressInst() to print the expanded
       version of the instruction instead of the compressed one (e.g,
       add s0, s0, a5 instead of c.add s0, a5) when -riscv-no-aliases
       is not passed.

This patch squashes D45119, D42780 and D41932. It was reviewed in  smaller patches by
asb, efriedma, apazos and mgrang.

Reviewers: asb, efriedma, apazos, llvm-commits, sabuasal

Reviewed By: sabuasal

Subscribers: mgorny, eraman, asb, rbar, johnrusso, simoncook, jordy.potman.lists, apazos, niosHD, kito-cheng, shiva0217, zzheng

Differential Revision: https://reviews.llvm.org/D45385

llvm-svn: 329455

llvm/include/llvm/MC/MCInst.h

@@ -150,6 +150,8 @@ class MCOperand {
 
   void print(raw_ostream &OS) const;
   void dump() const;
+  bool isBareSymbolRef() const;
+  bool evaluateAsConstantImm(int64_t &Imm) const;
 };
 
 template <> struct isPodLike<MCOperand> { static const bool value = true; };

llvm/lib/MC/MCInst.cpp

@@ -10,6 +10,7 @@
 #include "llvm/MC/MCInst.h"
 #include "llvm/MC/MCExpr.h"
 #include "llvm/MC/MCInstPrinter.h"
+#include "llvm/Support/Casting.h"
 #include "llvm/Support/Compiler.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/raw_ostream.h"
@@ -35,6 +36,23 @@ void MCOperand::print(raw_ostream &OS) const {
   OS << ">";
 }
 
+bool MCOperand::evaluateAsConstantImm(int64_t &Imm) const {
+  if (isImm()) {
+    Imm = getImm();
+    return true;
+  }
+  return false;
+}
+
+bool MCOperand::isBareSymbolRef() const {
+  assert(isExpr() &&
+         "isBareSymbolRef expects only expressions");
+  const MCExpr *Expr = getExpr();
+  MCExpr::ExprKind Kind = getExpr()->getKind();
+  return Kind == MCExpr::SymbolRef &&
+    cast<MCSymbolRefExpr>(Expr)->getKind() == MCSymbolRefExpr::VK_None;
+}
+
 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
 LLVM_DUMP_METHOD void MCOperand::dump() const {
   print(dbgs());

llvm/lib/Target/RISCV/AsmParser/RISCVAsmParser.cpp

@@ -26,6 +26,10 @@
 
 using namespace llvm;
 
+// Include the auto-generated portion of the compress emitter.
+#define GEN_COMPRESS_INSTR
+#include "RISCVGenCompressInstEmitter.inc"
+
 namespace {
 struct RISCVOperand;
 
@@ -595,10 +599,14 @@ bool RISCVAsmParser::MatchAndEmitInstruction(SMLoc IDLoc, unsigned &Opcode,
   switch (MatchInstructionImpl(Operands, Inst, ErrorInfo, MatchingInlineAsm)) {
   default:
     break;
-  case Match_Success:
+  case Match_Success: {
+    MCInst CInst;
+    bool Res = compressInst(CInst, Inst, getSTI(), Out.getContext());
+    CInst.setLoc(IDLoc);
     Inst.setLoc(IDLoc);
-    Out.EmitInstruction(Inst, getSTI());
+    Out.EmitInstruction((Res ? CInst : Inst), getSTI());
     return false;
+  }
   case Match_MissingFeature:
     return Error(IDLoc, "instruction use requires an option to be enabled");
   case Match_MnemonicFail:

llvm/lib/Target/RISCV/CMakeLists.txt

@@ -2,6 +2,7 @@ set(LLVM_TARGET_DEFINITIONS RISCV.td)
 
 tablegen(LLVM RISCVGenAsmMatcher.inc -gen-asm-matcher)
 tablegen(LLVM RISCVGenAsmWriter.inc -gen-asm-writer)
+tablegen(LLVM RISCVGenCompressInstEmitter.inc -gen-compress-inst-emitter)
 tablegen(LLVM RISCVGenDAGISel.inc -gen-dag-isel)
 tablegen(LLVM RISCVGenDisassemblerTables.inc -gen-disassembler)
 tablegen(LLVM RISCVGenInstrInfo.inc -gen-instr-info)

llvm/lib/Target/RISCV/InstPrinter/RISCVInstPrinter.cpp

@@ -13,6 +13,7 @@
 
 #include "RISCVInstPrinter.h"
 #include "MCTargetDesc/RISCVBaseInfo.h"
+#include "MCTargetDesc/RISCVMCExpr.h"
 #include "llvm/MC/MCAsmInfo.h"
 #include "llvm/MC/MCExpr.h"
 #include "llvm/MC/MCInst.h"
@@ -30,6 +31,10 @@ using namespace llvm;
 #define PRINT_ALIAS_INSTR
 #include "RISCVGenAsmWriter.inc"
 
+// Include the auto-generated portion of the compress emitter.
+#define GEN_UNCOMPRESS_INSTR
+#include "RISCVGenCompressInstEmitter.inc"
+
 static cl::opt<bool>
 NoAliases("riscv-no-aliases",
             cl::desc("Disable the emission of assembler pseudo instructions"),
@@ -38,8 +43,15 @@ NoAliases("riscv-no-aliases",
 
 void RISCVInstPrinter::printInst(const MCInst *MI, raw_ostream &O,
                                  StringRef Annot, const MCSubtargetInfo &STI) {
-  if (NoAliases || !printAliasInstr(MI, STI, O))
-    printInstruction(MI, STI, O);
+  bool Res = false;
+  const MCInst *NewMI = MI;
+  MCInst UncompressedMI;
+  if (!NoAliases)
+    Res = uncompressInst(UncompressedMI, *MI, MRI, STI);
+  if (Res)
+    NewMI = const_cast<MCInst*>(&UncompressedMI);
+  if (NoAliases || !printAliasInstr(NewMI, STI, O))
+    printInstruction(NewMI, STI, O);
   printAnnotation(O, Annot);
 }
 

llvm/lib/Target/RISCV/MCTargetDesc/RISCVMCExpr.cpp

@@ -12,6 +12,7 @@
 //
 //===----------------------------------------------------------------------===//
 
+#include "RISCV.h"
 #include "RISCVMCExpr.h"
 #include "llvm/MC/MCAssembler.h"
 #include "llvm/MC/MCContext.h"

llvm/lib/Target/RISCV/MCTargetDesc/RISCVMCExpr.h

@@ -20,6 +20,7 @@
 namespace llvm {
 
 class StringRef;
+class MCOperand;
 class RISCVMCExpr : public MCTargetExpr {
 public:
   enum VariantKind {

llvm/lib/Target/RISCV/RISCVAsmPrinter.cpp

@@ -14,6 +14,7 @@
 
 #include "RISCV.h"
 #include "InstPrinter/RISCVInstPrinter.h"
+#include "MCTargetDesc/RISCVMCExpr.h"
 #include "RISCVTargetMachine.h"
 #include "llvm/CodeGen/AsmPrinter.h"
 #include "llvm/CodeGen/MachineConstantPool.h"
@@ -48,6 +49,7 @@ class RISCVAsmPrinter : public AsmPrinter {
                              unsigned AsmVariant, const char *ExtraCode,
                              raw_ostream &OS) override;
 
+  void EmitToStreamer(MCStreamer &S, const MCInst &Inst);
   bool emitPseudoExpansionLowering(MCStreamer &OutStreamer,
                                    const MachineInstr *MI);
 
@@ -58,6 +60,15 @@ class RISCVAsmPrinter : public AsmPrinter {
 };
 }
 
+#define GEN_COMPRESS_INSTR
+#include "RISCVGenCompressInstEmitter.inc"
+void RISCVAsmPrinter::EmitToStreamer(MCStreamer &S, const MCInst &Inst) {
+  MCInst CInst;
+  bool Res = compressInst(CInst, Inst, *TM.getMCSubtargetInfo(),
+                          OutStreamer->getContext());
+  AsmPrinter::EmitToStreamer(*OutStreamer, Res ? CInst : Inst);
+}
+
 // Simple pseudo-instructions have their lowering (with expansion to real
 // instructions) auto-generated.
 #include "RISCVGenMCPseudoLowering.inc"

llvm/lib/Target/RISCV/RISCVInstrInfo.td

@@ -83,6 +83,14 @@ def uimmlog2xlen : Operand<XLenVT>, ImmLeaf<XLenVT, [{
   let ParserMatchClass = UImmLog2XLenAsmOperand;
   // TODO: should ensure invalid shamt is rejected when decoding.
   let DecoderMethod = "decodeUImmOperand<6>";
+  let MCOperandPredicate = [{
+    int64_t Imm;
+    if (!MCOp.evaluateAsConstantImm(Imm))
+      return false;
+    if (STI.getTargetTriple().isArch64Bit())
+      return  isUInt<6>(Imm);
+    return isUInt<5>(Imm);
+  }];
 }
 
 def uimm5 : Operand<XLenVT>, ImmLeaf<XLenVT, [{return isUInt<5>(Imm);}]> {
@@ -94,6 +102,12 @@ def simm12 : Operand<XLenVT>, ImmLeaf<XLenVT, [{return isInt<12>(Imm);}]> {
   let ParserMatchClass = SImmAsmOperand<12>;
   let EncoderMethod = "getImmOpValue";
   let DecoderMethod = "decodeSImmOperand<12>";
+  let MCOperandPredicate = [{
+    int64_t Imm;
+    if (MCOp.evaluateAsConstantImm(Imm))
+      return isInt<12>(Imm);
+    return MCOp.isBareSymbolRef();
+  }];
 }
 
 def uimm12 : Operand<XLenVT> {
@@ -106,19 +120,37 @@ def simm13_lsb0 : Operand<OtherVT> {
   let ParserMatchClass = SImmAsmOperand<13, "Lsb0">;
   let EncoderMethod = "getImmOpValueAsr1";
   let DecoderMethod = "decodeSImmOperandAndLsl1<13>";
+  let MCOperandPredicate = [{
+    int64_t Imm;
+    if (MCOp.evaluateAsConstantImm(Imm))
+      return isShiftedInt<12, 1>(Imm);
+    return MCOp.isBareSymbolRef();
+  }];
 }
 
 def uimm20 : Operand<XLenVT> {
   let ParserMatchClass = UImmAsmOperand<20>;
   let EncoderMethod = "getImmOpValue";
   let DecoderMethod = "decodeUImmOperand<20>";
+  let MCOperandPredicate = [{
+    int64_t Imm;
+    if (MCOp.evaluateAsConstantImm(Imm))
+      return isUInt<20>(Imm);
+    return MCOp.isBareSymbolRef();
+  }];
 }
 
 // A 21-bit signed immediate where the least significant bit is zero.
 def simm21_lsb0 : Operand<OtherVT> {
   let ParserMatchClass = SImmAsmOperand<21, "Lsb0">;
   let EncoderMethod = "getImmOpValueAsr1";
   let DecoderMethod = "decodeSImmOperandAndLsl1<21>";
+  let MCOperandPredicate = [{
+    int64_t Imm;
+    if (MCOp.evaluateAsConstantImm(Imm))
+      return isShiftedInt<20, 1>(Imm);
+    return MCOp.isBareSymbolRef();
+  }];
 }
 
 // A parameterized register class alternative to i32imm/i64imm from Target.td.