[RISCV] Add basic RV32E definitions and MC layer support

The RISC-V ISA defines RV32E as an alternative "base" instruction set
encoding, that differs from RV32I by having only 16 rather than 32 registers.
This patch adds basic definitions for RV32E as well as MC layer support
(assembling, disassembling) and tests. The only supported ABI on RV32E is
ILP32E.

Add a new RISCVFeatures::validate() helper to RISCVUtils which can be called
from codegen or MC layer libraries to validate the combination of TargetTriple
and FeatureBitSet. Other targets have similar checks (e.g. erroring if SPE is
enabled on PPC64 or oddspreg + o32 ABI on Mips), but they either duplicate the
checks (Mips), or fail to check for both codegen and MC codepaths (PPC).

Codegen for the ILP32E ABI support and RV32E codegen are left for a future
patch/patches.

Differential Revision: https://reviews.llvm.org/D59470

llvm-svn: 356744

9 files changed, 67 insertions, 15 deletions

diff --git a/llvm/lib/Target/RISCV/AsmParser/RISCVAsmParser.cpp b/llvm/lib/Target/RISCV/AsmParser/RISCVAsmParser.cpp
index 4202d5bfe19..ae7b648460b 100644
--- a/llvm/lib/Target/RISCV/AsmParser/RISCVAsmParser.cpp
+++ b/llvm/lib/Target/RISCV/AsmParser/RISCVAsmParser.cpp
@@ -47,6 +47,7 @@ class RISCVAsmParser : public MCTargetAsmParser {
 
   SMLoc getLoc() const { return getParser().getTok().getLoc(); }
   bool isRV64() const { return getSTI().hasFeature(RISCV::Feature64Bit); }
+  bool isRV32E() const { return getSTI().hasFeature(RISCV::FeatureRV32E); }
 
   RISCVTargetStreamer &getTargetStreamer() {
     MCTargetStreamer &TS = *getParser().getStreamer().getTargetStreamer();
@@ -910,11 +911,15 @@ bool RISCVAsmParser::MatchAndEmitInstruction(SMLoc IDLoc, unsigned &Opcode,
 
 // Attempts to match Name as a register (either using the default name or
 // alternative ABI names), setting RegNo to the matching register. Upon
-// failure, returns true and sets RegNo to 0.
-static bool matchRegisterNameHelper(unsigned &RegNo, StringRef Name) {
+// failure, returns true and sets RegNo to 0. If IsRV32E then registers
+// x16-x31 will be rejected.
+static bool matchRegisterNameHelper(bool IsRV32E, unsigned &RegNo,
+                                    StringRef Name) {
   RegNo = MatchRegisterName(Name);
   if (RegNo == 0)
     RegNo = MatchRegisterAltName(Name);
+  if (IsRV32E && RegNo >= RISCV::X16 && RegNo <= RISCV::X31)
+    RegNo = 0;
   return RegNo == 0;
 }
 
@@ -926,7 +931,7 @@ bool RISCVAsmParser::ParseRegister(unsigned &RegNo, SMLoc &StartLoc,
   RegNo = 0;
   StringRef Name = getLexer().getTok().getIdentifier();
 
-  if (matchRegisterNameHelper(RegNo, Name))
+  if (matchRegisterNameHelper(isRV32E(), RegNo, Name))
     return Error(StartLoc, "invalid register name");
 
   getParser().Lex(); // Eat identifier token.
@@ -954,7 +959,7 @@ OperandMatchResultTy RISCVAsmParser::parseRegister(OperandVector &Operands,
   case AsmToken::Identifier:
     StringRef Name = getLexer().getTok().getIdentifier();
     unsigned RegNo;
-    matchRegisterNameHelper(RegNo, Name);
+    matchRegisterNameHelper(isRV32E(), RegNo, Name);
 
     if (RegNo == 0) {
       if (HadParens)
diff --git a/llvm/lib/Target/RISCV/Disassembler/RISCVDisassembler.cpp b/llvm/lib/Target/RISCV/Disassembler/RISCVDisassembler.cpp
index 26d5bca8de2..0ec22fa80e1 100644
--- a/llvm/lib/Target/RISCV/Disassembler/RISCVDisassembler.cpp
+++ b/llvm/lib/Target/RISCV/Disassembler/RISCVDisassembler.cpp
@@ -69,7 +69,13 @@ static const unsigned GPRDecoderTable[] = {
 static DecodeStatus DecodeGPRRegisterClass(MCInst &Inst, uint64_t RegNo,
                                            uint64_t Address,
                                            const void *Decoder) {
-  if (RegNo > array_lengthof(GPRDecoderTable))
+  const FeatureBitset &FeatureBits =
+      static_cast<const MCDisassembler *>(Decoder)
+          ->getSubtargetInfo()
+          .getFeatureBits();
+  bool IsRV32E = FeatureBits[RISCV::FeatureRV32E];
+
+  if (RegNo > array_lengthof(GPRDecoderTable) || (IsRV32E && RegNo > 15))
     return MCDisassembler::Fail;
 
   // We must define our own mapping from RegNo to register identifier.
diff --git a/llvm/lib/Target/RISCV/MCTargetDesc/RISCVAsmBackend.h b/llvm/lib/Target/RISCV/MCTargetDesc/RISCVAsmBackend.h
index 54d58480e10..248ef20f927 100644
--- a/llvm/lib/Target/RISCV/MCTargetDesc/RISCVAsmBackend.h
+++ b/llvm/lib/Target/RISCV/MCTargetDesc/RISCVAsmBackend.h
@@ -36,6 +36,7 @@ public:
         TargetOptions(Options) {
     TargetABI = RISCVABI::computeTargetABI(
         STI.getTargetTriple(), STI.getFeatureBits(), Options.getABIName());
+    RISCVFeatures::validate(STI.getTargetTriple(), STI.getFeatureBits());
   }
   ~RISCVAsmBackend() override {}
 
diff --git a/llvm/lib/Target/RISCV/RISCV.td b/llvm/lib/Target/RISCV/RISCV.td
index 3936da677a5..b166418a622 100644
--- a/llvm/lib/Target/RISCV/RISCV.td
+++ b/llvm/lib/Target/RISCV/RISCV.td
@@ -54,6 +54,12 @@ def IsRV32 : Predicate<"!Subtarget->is64Bit()">,
 def RV64           : HwMode<"+64bit">;
 def RV32           : HwMode<"-64bit">;
 
+def FeatureRV32E
+    : SubtargetFeature<"e", "IsRV32E", "true",
+                       "Implements RV32E (provides 16 rather than 32 GPRs)">;
+def IsRV32E : Predicate<"Subtarget->isRV32E()">,
+                        AssemblerPredicate<"FeatureRV32E">;
+
 def FeatureRelax
     : SubtargetFeature<"relax", "EnableLinkerRelax", "true",
                        "Enable Linker relaxation.">;
diff --git a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
index 94bd948c694..12e07143b7b 100644
--- a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
+++ b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
@@ -43,6 +43,9 @@ RISCVTargetLowering::RISCVTargetLowering(const TargetMachine &TM,
                                          const RISCVSubtarget &STI)
     : TargetLowering(TM), Subtarget(STI) {
 
+  if (Subtarget.isRV32E())
+    report_fatal_error("Codegen not yet implemented for RV32E");
+
   RISCVABI::ABI ABI = Subtarget.getTargetABI();
   assert(ABI != RISCVABI::ABI_Unknown && "Improperly initialised target ABI");
 
diff --git a/llvm/lib/Target/RISCV/RISCVSubtarget.cpp b/llvm/lib/Target/RISCV/RISCVSubtarget.cpp
index 0c7355cab38..6902ed75d85 100644
--- a/llvm/lib/Target/RISCV/RISCVSubtarget.cpp
+++ b/llvm/lib/Target/RISCV/RISCVSubtarget.cpp
@@ -39,6 +39,7 @@ RISCVSubtarget &RISCVSubtarget::initializeSubtargetDependencies(
   }
 
   TargetABI = RISCVABI::computeTargetABI(TT, getFeatureBits(), ABIName);
+  RISCVFeatures::validate(TT, getFeatureBits());
   return *this;
 }
 
diff --git a/llvm/lib/Target/RISCV/RISCVSubtarget.h b/llvm/lib/Target/RISCV/RISCVSubtarget.h
index 6c10ee44fd6..106ff49f021 100644
--- a/llvm/lib/Target/RISCV/RISCVSubtarget.h
+++ b/llvm/lib/Target/RISCV/RISCVSubtarget.h
@@ -36,6 +36,7 @@ class RISCVSubtarget : public RISCVGenSubtargetInfo {
   bool HasStdExtD = false;
   bool HasStdExtC = false;
   bool HasRV64 = false;
+  bool IsRV32E = false;
   bool EnableLinkerRelax = false;
   unsigned XLen = 32;
   MVT XLenVT = MVT::i32;
@@ -80,6 +81,7 @@ public:
   bool hasStdExtD() const { return HasStdExtD; }
   bool hasStdExtC() const { return HasStdExtC; }
   bool is64Bit() const { return HasRV64; }
+  bool isRV32E() const { return IsRV32E; }
   bool enableLinkerRelax() const { return EnableLinkerRelax; }
   MVT getXLenVT() const { return XLenVT; }
   unsigned getXLen() const { return XLen; }
diff --git a/llvm/lib/Target/RISCV/Utils/RISCVBaseInfo.cpp b/llvm/lib/Target/RISCV/Utils/RISCVBaseInfo.cpp
index bb967cb0248..bc5395768ca 100644
--- a/llvm/lib/Target/RISCV/Utils/RISCVBaseInfo.cpp
+++ b/llvm/lib/Target/RISCV/Utils/RISCVBaseInfo.cpp
@@ -22,15 +22,18 @@ ABI computeTargetABI(const Triple &TT, FeatureBitset FeatureBits,
                        .Case("lp64d", ABI_LP64D)
                        .Default(ABI_Unknown);
 
+  bool IsRV64 = TT.isArch64Bit();
+  bool IsRV32E = FeatureBits[RISCV::FeatureRV32E];
+
   if (!ABIName.empty() && TargetABI == ABI_Unknown) {
     errs()
         << "'" << ABIName
         << "' is not a recognized ABI for this target (ignoring target-abi)\n";
-  } else if (ABIName.startswith("ilp32") && TT.isArch64Bit()) {
+  } else if (ABIName.startswith("ilp32") && IsRV64) {
     errs() << "32-bit ABIs are not supported for 64-bit targets (ignoring "
               "target-abi)\n";
     TargetABI = ABI_Unknown;
-  } else if (ABIName.startswith("lp64") && !TT.isArch64Bit()) {
+  } else if (ABIName.startswith("lp64") && !IsRV64) {
     errs() << "64-bit ABIs are not supported for 32-bit targets (ignoring "
               "target-abi)\n";
     TargetABI = ABI_Unknown;
@@ -44,17 +47,34 @@ ABI computeTargetABI(const Triple &TT, FeatureBitset FeatureBits,
               "doesn't support the D instruction set extension (ignoring "
               "target-abi)\n";
     TargetABI = ABI_Unknown;
+  } else if (IsRV32E && TargetABI != ABI_ILP32E && TargetABI != ABI_Unknown) {
+    errs()
+        << "Only the ilp32e ABI is supported for RV32E (ignoring target-abi)\n";
+    TargetABI = ABI_Unknown;
   }
 
-  // For now, default to the ilp32/lp64 if no explicit ABI is given or an
-  // invalid/unrecognised string is given. In the future, it might be worth
-  // changing this to default to ilp32f/lp64f and ilp32d/lp64d when hardware
-  // support for floating point is present.
-  if (TargetABI == ABI_Unknown) {
-    TargetABI = TT.isArch64Bit() ? ABI_LP64 : ABI_ILP32;
-  }
+  if (TargetABI != ABI_Unknown)
+    return TargetABI;
 
-  return TargetABI;
+  // For now, default to the ilp32/ilp32e/lp64 ABI if no explicit ABI is given
+  // or an invalid/unrecognised string is given. In the future, it might be
+  // worth changing this to default to ilp32f/lp64f and ilp32d/lp64d when
+  // hardware support for floating point is present.
+  if (IsRV32E)
+    return ABI_ILP32E;
+  if (IsRV64)
+    return ABI_LP64;
+  return ABI_ILP32;
 }
 } // namespace RISCVABI
+
+namespace RISCVFeatures {
+
+void validate(const Triple &TT, const FeatureBitset &FeatureBits) {
+  if (TT.isArch64Bit() && FeatureBits[RISCV::FeatureRV32E])
+    report_fatal_error("RV32E can't be enabled for an RV64 target");
+}
+
+} // namespace RISCVFeatures
+
 } // namespace llvm
diff --git a/llvm/lib/Target/RISCV/Utils/RISCVBaseInfo.h b/llvm/lib/Target/RISCV/Utils/RISCVBaseInfo.h
index 4ace9ddbfcd..1ccd2254f50 100644
--- a/llvm/lib/Target/RISCV/Utils/RISCVBaseInfo.h
+++ b/llvm/lib/Target/RISCV/Utils/RISCVBaseInfo.h
@@ -172,6 +172,14 @@ ABI computeTargetABI(const Triple &TT, FeatureBitset FeatureBits,
 
 } // namespace RISCVABI
 
+namespace RISCVFeatures {
+
+// Validates if the given combination of features are valid for the target
+// triple. Exits with report_fatal_error if not.
+void validate(const Triple &TT, const FeatureBitset &FeatureBits);
+
+} // namespace RISCVFeatures
+
 } // namespace llvm
 
 #endif