[Exegesis][RISCV] Add RVV support

mshockwave · mshockwave · commit a0651b5b9b3a · 2025-02-25T10:56:32.000-08:00
TBA...
diff --git a/llvm/lib/Target/RISCV/MCTargetDesc/RISCVBaseInfo.h b/llvm/lib/Target/RISCV/MCTargetDesc/RISCVBaseInfo.h
@@ -432,7 +432,44 @@ enum RoundingMode {
   RNE = 1,
   RDN = 2,
   ROD = 3,
+  Invalid
 };
+
+inline static StringRef roundingModeToString(RoundingMode RndMode) {
+  switch (RndMode) {
+  default:
+    llvm_unreachable("Unknown vector fixed-point rounding mode");
+  case RISCVVXRndMode::RNU:
+    return "rnu";
+  case RISCVVXRndMode::RNE:
+    return "rne";
+  case RISCVVXRndMode::RDN:
+    return "rdn";
+  case RISCVVXRndMode::ROD:
+    return "rod";
+  }
+}
+
+inline static RoundingMode stringToRoundingMode(StringRef Str) {
+  return StringSwitch<RoundingMode>(Str)
+      .Case("rnu", RISCVVXRndMode::RNU)
+      .Case("rne", RISCVVXRndMode::RNE)
+      .Case("rdn", RISCVVXRndMode::RDN)
+      .Case("rod", RISCVVXRndMode::ROD)
+      .Default(RISCVVXRndMode::Invalid);
+}
+
+inline static bool isValidRoundingMode(unsigned Mode) {
+  switch (Mode) {
+  default:
+    return false;
+  case RISCVVXRndMode::RNU:
+  case RISCVVXRndMode::RNE:
+  case RISCVVXRndMode::RDN:
+  case RISCVVXRndMode::ROD:
+    return true;
+  }
+}
 } // namespace RISCVVXRndMode
 
 //===----------------------------------------------------------------------===//
diff --git a/llvm/test/tools/llvm-exegesis/RISCV/rvv/eligible-inst.test b/llvm/test/tools/llvm-exegesis/RISCV/rvv/eligible-inst.test
@@ -0,0 +1,10 @@
+# RUN: llvm-exegesis -mtriple=riscv64 -mcpu=sifive-x280 -benchmark-phase=assemble-measured-code --mode=latency \
+# RUN:    --opcode-name=PseudoVCOMPRESS_VM_M2_E8,PseudoVCPOP_M_B32 | FileCheck %s --allow-empty --check-prefix=LATENCY
+# RUN: llvm-exegesis -mtriple=riscv64 -mcpu=sifive-x280 -benchmark-phase=assemble-measured-code --mode=inverse_throughput \
+# RUN:    --opcode-name=PseudoVCOMPRESS_VM_M2_E8,PseudoVCPOP_M_B32 --min-instructions=100 | FileCheck %s --check-prefix=RTHROUGHPUT
+
+# LATENCY-NOT: PseudoVCOMPRESS_VM_M2_E8
+# LATENCY-NOT: PseudoVCPOP_M_B32
+
+# RTHROUGHPUT: PseudoVCOMPRESS_VM_M2_E8
+# RTHROUGHPUT: PseudoVCPOP_M_B32
diff --git a/llvm/test/tools/llvm-exegesis/RISCV/rvv/explicit-sew.test b/llvm/test/tools/llvm-exegesis/RISCV/rvv/explicit-sew.test
@@ -0,0 +1,7 @@
+# RUN: llvm-exegesis -mtriple=riscv64 -mcpu=sifive-x280 -benchmark-phase=assemble-measured-code --mode=latency --opcode-name=PseudoVFWREDUSUM_VS_M1_E32 \
+# RUN:    --max-configs-per-opcode=1000 --min-instructions=100 | FileCheck %s
+
+# Make sure none of the config has SEW other than e32
+# CHECK: PseudoVFWREDUSUM_VS_M1_E32
+# CHECK: SEW: e32
+# CHECK-NOT: SEW: e{{(8|16|64)}}
diff --git a/llvm/test/tools/llvm-exegesis/RISCV/rvv/filter.test b/llvm/test/tools/llvm-exegesis/RISCV/rvv/filter.test
@@ -0,0 +1,6 @@
+# RUN: llvm-exegesis -mtriple=riscv64 -mcpu=sifive-x280 -benchmark-phase=assemble-measured-code --mode=inverse_throughput --opcode-name=PseudoVNCLIPU_WX_M1_MASK \
+# RUN:    --riscv-filter-config='vtype = {VXRM: rod, AVL: VLMAX, SEW: e(8|16), Policy: ta/mu}' --max-configs-per-opcode=1000 --min-instructions=100 | FileCheck %s
+
+# CHECK: config:          'vtype = {VXRM: rod, AVL: VLMAX, SEW: e8, Policy: ta/mu}'
+# CHECK: config:          'vtype = {VXRM: rod, AVL: VLMAX, SEW: e16, Policy: ta/mu}'
+# CHECK-NOT: config:          'vtype = {VXRM: rod, AVL: VLMAX, SEW: e(32|64), Policy: ta/mu}'
diff --git a/llvm/test/tools/llvm-exegesis/RISCV/rvv/reduction.test b/llvm/test/tools/llvm-exegesis/RISCV/rvv/reduction.test
@@ -0,0 +1,7 @@
+# RUN: llvm-exegesis -mtriple=riscv64 -mcpu=sifive-p670 -benchmark-phase=assemble-measured-code --mode=latency --opcode-name=PseudoVWREDSUMU_VS_M8_E32 --min-instructions=100 | \
+# RUN:    FileCheck %s
+
+# Make sure reduction ops don't have alias between vd and vs1
+# CHECK:      instructions:
+# CHECK-NEXT: PseudoVWREDSUMU_VS_M8_E32
+# CHECK-NOT:  V[[REG:[0-9]+]] V[[REG]] V{{[0-9]+}}M8 V[[REG]]
diff --git a/llvm/test/tools/llvm-exegesis/RISCV/rvv/self-aliasing.test b/llvm/test/tools/llvm-exegesis/RISCV/rvv/self-aliasing.test
@@ -0,0 +1,6 @@
+# RUN: llvm-exegesis -mtriple=riscv64 -mcpu=sifive-x280 -benchmark-phase=assemble-measured-code --mode=latency --opcode-name=PseudoVXOR_VX_M4 --min-instructions=100 | \
+# RUN:    FileCheck %s
+
+# Make sure all def / use operands are the same in latency mode.
+# CHECK:      instructions:
+# CHECK-NEXT: PseudoVXOR_VX_M4 V[[REG:[0-9]+]]M4 V[[REG]]M4 V[[REG]]M4 X{{.*}}
diff --git a/llvm/test/tools/llvm-exegesis/RISCV/rvv/skip-rm.test b/llvm/test/tools/llvm-exegesis/RISCV/rvv/skip-rm.test
@@ -0,0 +1,12 @@
+# RUN: llvm-exegesis -mtriple=riscv64 -mcpu=sifive-x280 -benchmark-phase=assemble-measured-code --mode=latency --opcode-name=PseudoVAADDU_VV_M1 \
+# RUN:    --riscv-enumerate-rounding-modes=false --max-configs-per-opcode=1000 --min-instructions=100 | FileCheck %s --check-prefix=VXRM
+# RUN: llvm-exegesis -mtriple=riscv64 -mcpu=sifive-x280 -benchmark-phase=assemble-measured-code --mode=latency --opcode-name=PseudoVFADD_VFPR16_M1_E16 \
+# RUN:    --riscv-enumerate-rounding-modes=false --max-configs-per-opcode=1000 --min-instructions=100 | FileCheck %s --check-prefix=FRM
+
+# VXRM: PseudoVAADDU_VV_M1
+# VXRM: VXRM: rnu
+# VXRM-NOT: VXRM: {{(rne|rdn|rod)}}
+
+# FRM: PseudoVFADD_VFPR16_M1_E16
+# FRM: FRM: rne
+# FRM-NOT: FRM: {{(rtz|rdn|rup|rmm|dyn)}}
diff --git a/llvm/test/tools/llvm-exegesis/RISCV/rvv/valid-sew-zvk.test b/llvm/test/tools/llvm-exegesis/RISCV/rvv/valid-sew-zvk.test
@@ -0,0 +1,33 @@
+# RUN: llvm-exegesis -mtriple=riscv64 -mcpu=sifive-p670 -benchmark-phase=assemble-measured-code --mode=inverse_throughput \
+# RUN:    --opcode-name=PseudoVAESDF_VS_M1_M1 --max-configs-per-opcode=1000 --min-instructions=100 | \
+# RUN:    FileCheck %s --check-prefix=ZVK
+# RUN: llvm-exegesis -mtriple=riscv64 -mcpu=sifive-p670 -benchmark-phase=assemble-measured-code --mode=inverse_throughput \
+# RUN:    --opcode-name=PseudoVGHSH_VV_M1 --max-configs-per-opcode=1000 --min-instructions=100 | \
+# RUN:    FileCheck %s --check-prefix=ZVK
+# RUN: llvm-exegesis -mtriple=riscv64 -mcpu=sifive-p670 -benchmark-phase=assemble-measured-code --mode=inverse_throughput \
+# RUN:    --opcode-name=PseudoVSM4K_VI_M1 --max-configs-per-opcode=1000 --min-instructions=100 | \
+# RUN:    FileCheck %s --check-prefix=ZVK
+# RUN: llvm-exegesis -mtriple=riscv64 -mcpu=sifive-p670 -benchmark-phase=assemble-measured-code --mode=inverse_throughput \
+# RUN:    --opcode-name=PseudoVSM3C_VI_M2 --max-configs-per-opcode=1000 --min-instructions=100 | \
+# RUN:    FileCheck %s --check-prefix=ZVK
+# RUN: llvm-exegesis -mtriple=riscv64 -mcpu=sifive-p670 -benchmark-phase=assemble-measured-code --mode=inverse_throughput \
+# RUN:    --opcode-name=PseudoVSHA2MS_VV_M1_E32 --max-configs-per-opcode=1000 --min-instructions=100 | \
+# RUN:    FileCheck %s --allow-empty --check-prefix=ZVKNH
+# RUN: llvm-exegesis -mtriple=riscv64 -mcpu=sifive-p670 -benchmark-phase=assemble-measured-code --mode=inverse_throughput \
+# RUN:    --opcode-name=PseudoVSHA2MS_VV_M2_E64 --max-configs-per-opcode=1000 --min-instructions=100 | \
+# RUN:    FileCheck %s --allow-empty --check-prefix=ZVKNH
+# RUN: llvm-exegesis -mtriple=riscv64 -mcpu=sifive-p670 -benchmark-phase=assemble-measured-code --mode=inverse_throughput \
+# RUN:    --opcode-name=PseudoVSM3C_VI_M1 --max-configs-per-opcode=1000 --min-instructions=100 | \
+# RUN:    FileCheck %s --allow-empty --check-prefix=EMPTY
+
+# Most vector crypto only supports SEW=32, except Zvknhb which also supports SEW=64
+# ZVK-NOT: SEW: e{{(8|16)}}
+# ZVK: SEW: e32
+# ZVK-NOT: SEW: e64
+
+# ZVKNH(A|B) can either have SEW=32 (EGW=128) or SEW=64 (EGW=256)
+
+# ZVKNH-NOT: SEW: e{{(8|16)}}
+# ZVKNH: SEW: e{{(32|64)}}
+
+# EMPTY-NOT: SEW: e{{(8|16|32|64)}}
diff --git a/llvm/test/tools/llvm-exegesis/RISCV/rvv/valid-sew.test b/llvm/test/tools/llvm-exegesis/RISCV/rvv/valid-sew.test
@@ -0,0 +1,41 @@
+# RUN: llvm-exegesis -mtriple=riscv64 -mcpu=sifive-x280 -benchmark-phase=assemble-measured-code --mode=latency --opcode-name=PseudoVMUL_VV_MF4_MASK \
+# RUN:    --max-configs-per-opcode=1000 --min-instructions=100 | FileCheck %s --check-prefix=FRAC-LMUL
+# RUN: llvm-exegesis -mtriple=riscv64 -mcpu=sifive-x280 -benchmark-phase=assemble-measured-code --mode=latency \
+# RUN:    --opcode-name=PseudoVFADD_VFPR16_M1_E16,PseudoVFADD_VV_M2_E16,PseudoVFCLASS_V_MF2 --max-configs-per-opcode=1000 --min-instructions=100 | \
+# RUN:    FileCheck %s --check-prefix=FP
+# RUN: llvm-exegesis -mtriple=riscv64 -mcpu=sifive-x280 -benchmark-phase=assemble-measured-code --mode=inverse_throughput \
+# RUN:    --opcode-name=PseudoVSEXT_VF8_M2,PseudoVZEXT_VF8_M2 --max-configs-per-opcode=1000 --min-instructions=100 | \
+# RUN:    FileCheck %s --check-prefix=VEXT
+# RUN: llvm-exegesis -mtriple=riscv64 -mcpu=sifive-p470 -benchmark-phase=assemble-measured-code --mode=latency \
+# RUN:    --opcode-name=PseudoVFREDUSUM_VS_M1_E16 --max-configs-per-opcode=1000 --min-instructions=100 | \
+# RUN:    FileCheck %s --check-prefix=VFRED --allow-empty
+
+# Make sure only the supported SEWs are generated for fractional LMUL.
+# FRAC-LMUL: PseudoVMUL_VV_MF4_MASK
+# FRAC-LMUL: SEW: e8
+# FRAC-LMUL: SEW: e16
+# FRAC-LMUL-NOT: SEW: e{{(32|64)}}
+
+# Make sure only SEWs that are equal to the supported FLEN are generated
+# FP: PseudoVFADD_VFPR16_M1_E16
+# FP-NOT: SEW: e8
+# FP: PseudoVFADD_VV_M2_E16
+# FP-NOT: SEW: e8
+# FP: PseudoVFCLASS_V_MF2
+# FP-NOT: SEW: e8
+
+# VS/ZEXT can only operate on SEW that will not lead to invalid EEW on the
+# source operand.
+# VEXT: PseudoVSEXT_VF8_M2
+# VEXT-NOT: SEW: e8
+# VEXT-NOT: SEW: e16
+# VEXT-NOT: SEW: e32
+# VEXT: SEW: e64
+# VEXT: PseudoVZEXT_VF8_M2
+# VEXT-NOT: SEW: e8
+# VEXT-NOT: SEW: e16
+# VEXT-NOT: SEW: e32
+# VEXT: SEW: e64
+
+# P470 doesn't have Zvfh so 16-bit vfredusum shouldn't exist
+# VFRED-NOT: PseudoVFREDUSUM_VS_M1_E16
diff --git a/llvm/test/tools/llvm-exegesis/RISCV/rvv/vlmax-only.test b/llvm/test/tools/llvm-exegesis/RISCV/rvv/vlmax-only.test
@@ -0,0 +1,7 @@
+# RUN: llvm-exegesis -mtriple=riscv64 -mcpu=sifive-x280 -benchmark-phase=assemble-measured-code --mode=latency --opcode-name=PseudoVFWREDUSUM_VS_M1_E32 \
+# RUN:    --riscv-vlmax-for-vl --max-configs-per-opcode=1000 --min-instructions=100 | FileCheck %s
+
+# Only allow VLMAX for AVL when -riscv-vlmax-for-vl is present
+# CHECK: PseudoVFWREDUSUM_VS_M1_E32
+# CHECK: AVL: VLMAX
+# CHECK-NOT: AVL: {{(simm5|<MCOperand: .*>)}}
diff --git a/llvm/test/tools/llvm-exegesis/RISCV/rvv/vtype-rm-setup.test b/llvm/test/tools/llvm-exegesis/RISCV/rvv/vtype-rm-setup.test
@@ -0,0 +1,13 @@
+# RUN: llvm-exegesis -mtriple=riscv64 -mcpu=sifive-x280 -benchmark-phase=assemble-measured-code --mode=latency --opcode-name=PseudoVFWREDUSUM_VS_M1_E32 \
+# RUN:    --max-configs-per-opcode=1 --min-instructions=100 --dump-object-to-disk=%t.o > %t.txt
+# RUN: llvm-objdump --triple=riscv64 -d %t.o | FileCheck %s --check-prefix=VFWREDUSUM
+# RUN: llvm-exegesis -mtriple=riscv64 -mcpu=sifive-x280 -benchmark-phase=assemble-measured-code --mode=latency --opcode-name=PseudoVSSRL_VX_MF4 \
+# RUN:    --max-configs-per-opcode=1 --min-instructions=100 --dump-object-to-disk=%t.o > %t.txt
+# RUN: llvm-objdump --triple=riscv64 -d %t.o | FileCheck %s --check-prefix=VSSRL
+
+# Make sure the correct VSETVL / VXRM write / FRM write instructions are generated
+# VFWREDUSUM: vsetvli {{.*}}, zero, e32, m1, tu, ma
+# VFWREDUSUM: fsrmi   {{.*}}, 0x0
+
+# VSSRL: vsetvli {{.*}}, zero, e8, mf4, tu, ma
+# VSSRL: csrwi   vxrm, 0x0
diff --git a/llvm/tools/llvm-exegesis/lib/MCInstrDescView.cpp b/llvm/tools/llvm-exegesis/lib/MCInstrDescView.cpp
@@ -50,6 +50,8 @@ bool Operand::isTied() const { return TiedToIndex.has_value(); }
 
 bool Operand::isVariable() const { return VariableIndex.has_value(); }
 
+bool Operand::isEarlyClobber() const { return IsEarlyClobber; }
+
 bool Operand::isMemory() const {
   return isExplicit() &&
          getExplicitOperandInfo().OperandType == MCOI::OPERAND_MEMORY;
@@ -115,6 +117,8 @@ Instruction::create(const MCInstrInfo &InstrInfo,
     Operand Operand;
     Operand.Index = OpIndex;
     Operand.IsDef = (OpIndex < Description->getNumDefs());
+    Operand.IsEarlyClobber =
+        (Description->getOperandConstraint(OpIndex, MCOI::EARLY_CLOBBER) != -1);
     // TODO(gchatelet): Handle isLookupPtrRegClass.
     if (OpInfo.RegClass >= 0)
       Operand.Tracker = &RATC.getRegisterClass(OpInfo.RegClass);
diff --git a/llvm/tools/llvm-exegesis/lib/MCInstrDescView.h b/llvm/tools/llvm-exegesis/lib/MCInstrDescView.h
@@ -72,6 +72,7 @@ struct Operand {
   bool isVariable() const;
   bool isMemory() const;
   bool isImmediate() const;
+  bool isEarlyClobber() const;
   unsigned getIndex() const;
   unsigned getTiedToIndex() const;
   unsigned getVariableIndex() const;
@@ -82,6 +83,7 @@ struct Operand {
   // Please use the accessors above and not the following fields.
   std::optional<uint8_t> Index;
   bool IsDef = false;
+  bool IsEarlyClobber = false;
   const RegisterAliasingTracker *Tracker = nullptr; // Set for Register Op.
   const MCOperandInfo *Info = nullptr;              // Set for Explicit Op.
   std::optional<uint8_t> TiedToIndex;               // Set for Reg&Explicit Op.
@@ -115,6 +117,8 @@ struct Instruction {
   Instruction &operator=(const Instruction &) = delete;
   Instruction &operator=(Instruction &&) = delete;
 
+  unsigned getOpcode() const { return Description.getOpcode(); }
+
   // Returns the Operand linked to this Variable.
   // In case the Variable is tied, the primary (i.e. Def) Operand is returned.
   const Operand &getPrimaryOperand(const Variable &Var) const;
diff --git a/llvm/tools/llvm-exegesis/lib/RISCV/CMakeLists.txt b/llvm/tools/llvm-exegesis/lib/RISCV/CMakeLists.txt
@@ -14,6 +14,8 @@ set(LLVM_LINK_COMPONENTS
 add_llvm_library(LLVMExegesisRISCV
   DISABLE_LLVM_LINK_LLVM_DYLIB
   STATIC
+  RISCVExegesisPreprocessing.cpp
+  RISCVExegesisPostprocessing.cpp
   Target.cpp
 
   DEPENDS
diff --git a/llvm/tools/llvm-exegesis/lib/RISCV/RISCVExegesisPasses.h b/llvm/tools/llvm-exegesis/lib/RISCV/RISCVExegesisPasses.h
@@ -0,0 +1,19 @@
+//===- RISCVExegesisPasses.h - RISC-V specific Exegesis Passes --*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_TOOLS_EXEGESIS_LIB_RISCV_RISCVEXEGESISPASSES_H
+#define LLVM_TOOLS_EXEGESIS_LIB_RISCV_RISCVEXEGESISPASSES_H
+namespace llvm {
+class FunctionPass;
+
+namespace exegesis {
+FunctionPass *createRISCVPreprocessingPass();
+FunctionPass *createRISCVPostprocessingPass();
+} // namespace exegesis
+} // namespace llvm
+#endif
diff --git a/llvm/tools/llvm-exegesis/lib/RISCV/RISCVExegesisPostprocessing.cpp b/llvm/tools/llvm-exegesis/lib/RISCV/RISCVExegesisPostprocessing.cpp
@@ -0,0 +1,130 @@
+//===- RISCVExegesisPostprocessing.cpp - Post processing MI for exegesis---===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+// \file
+// Currently there is only one post-processing we need to do for exegesis:
+// Assign a physical register to VSETVL's rd if it's not X0 (i.e. VLMAX).
+//
+//===----------------------------------------------------------------------===//
+
+#include "RISCV.h"
+#include "RISCVExegesisPasses.h"
+#include "llvm/CodeGen/MachineFunctionPass.h"
+#include "llvm/CodeGen/MachineRegisterInfo.h"
+#include "llvm/Support/Debug.h"
+
+using namespace llvm;
+
+#define DEBUG_TYPE "riscv-exegesis-post-processing"
+
+namespace {
+struct RISCVExegesisPostprocessing : public MachineFunctionPass {
+  static char ID;
+
+  RISCVExegesisPostprocessing() : MachineFunctionPass(ID) {}
+
+  bool runOnMachineFunction(MachineFunction &MF) override;
+
+  void getAnalysisUsage(AnalysisUsage &AU) const override {
+    AU.setPreservesCFG();
+    MachineFunctionPass::getAnalysisUsage(AU);
+  }
+
+private:
+  // Extremely simple register allocator that picks a register that hasn't
+  // been defined or used in this function.
+  Register allocateGPRRegister(const MachineFunction &MF,
+                               const MachineRegisterInfo &MRI);
+
+  bool processVSETVL(MachineInstr &MI, MachineRegisterInfo &MRI);
+  bool processWriteFRM(MachineInstr &MI, MachineRegisterInfo &MRI);
+};
+} // anonymous namespace
+
+char RISCVExegesisPostprocessing::ID = 0;
+
+bool RISCVExegesisPostprocessing::runOnMachineFunction(MachineFunction &MF) {
+  bool Changed = false;
+  for (auto &MBB : MF)
+    for (auto &MI : MBB) {
+      unsigned Opcode = MI.getOpcode();
+      switch (Opcode) {
+      case RISCV::VSETVLI:
+      case RISCV::VSETVL:
+      case RISCV::PseudoVSETVLI:
+      case RISCV::PseudoVSETVLIX0:
+        Changed |= processVSETVL(MI, MF.getRegInfo());
+        break;
+      case RISCV::SwapFRMImm:
+      case RISCV::WriteFRM:
+        Changed |= processWriteFRM(MI, MF.getRegInfo());
+        break;
+      default:
+        break;
+      }
+    }
+
+  if (Changed)
+    MF.getRegInfo().clearVirtRegs();
+
+  LLVM_DEBUG(MF.print(dbgs() << "===After RISCVExegesisPostprocessing===\n");
+             dbgs() << "\n");
+
+  return Changed;
+}
+
+Register RISCVExegesisPostprocessing::allocateGPRRegister(
+    const MachineFunction &MF, const MachineRegisterInfo &MRI) {
+  const auto &TRI = *MRI.getTargetRegisterInfo();
+
+  const TargetRegisterClass *GPRClass =
+      TRI.getRegClass(RISCV::GPRJALRRegClassID);
+  BitVector Candidates = TRI.getAllocatableSet(MF, GPRClass);
+
+  for (unsigned SetIdx : Candidates.set_bits()) {
+    if (MRI.reg_empty(Register(SetIdx)))
+      return Register(SetIdx);
+  }
+
+  // All bets are off, assign a fixed one.
+  return RISCV::X5;
+}
+
+bool RISCVExegesisPostprocessing::processVSETVL(MachineInstr &MI,
+                                                MachineRegisterInfo &MRI) {
+  bool Changed = false;
+  // Replace both AVL and VL (i.e. the result) operands with physical
+  // registers.
+  for (unsigned Idx = 0U; Idx < 2; ++Idx)
+    if (MI.getOperand(Idx).isReg()) {
+      Register RegOp = MI.getOperand(Idx).getReg();
+      if (RegOp.isVirtual()) {
+        MRI.replaceRegWith(RegOp, allocateGPRRegister(*MI.getMF(), MRI));
+        Changed = true;
+      }
+    }
+
+  return Changed;
+}
+
+bool RISCVExegesisPostprocessing::processWriteFRM(MachineInstr &MI,
+                                                  MachineRegisterInfo &MRI) {
+  // The virtual register will be the first operand in both SwapFRMImm and
+  // WriteFRM.
+  if (MI.getOperand(0).isReg()) {
+    Register DestReg = MI.getOperand(0).getReg();
+    if (DestReg.isVirtual()) {
+      MRI.replaceRegWith(DestReg, allocateGPRRegister(*MI.getMF(), MRI));
+      return true;
+    }
+  }
+  return false;
+}
+
+FunctionPass *llvm::exegesis::createRISCVPostprocessingPass() {
+  return new RISCVExegesisPostprocessing();
+}
diff --git a/llvm/tools/llvm-exegesis/lib/RISCV/RISCVExegesisPreprocessing.cpp b/llvm/tools/llvm-exegesis/lib/RISCV/RISCVExegesisPreprocessing.cpp
diff --git a/llvm/tools/llvm-exegesis/lib/RISCV/Target.cpp b/llvm/tools/llvm-exegesis/lib/RISCV/Target.cpp
diff --git a/llvm/tools/llvm-exegesis/lib/SerialSnippetGenerator.cpp b/llvm/tools/llvm-exegesis/lib/SerialSnippetGenerator.cpp
diff --git a/llvm/tools/llvm-exegesis/lib/Target.cpp b/llvm/tools/llvm-exegesis/lib/Target.cpp
diff --git a/llvm/tools/llvm-exegesis/lib/Target.h b/llvm/tools/llvm-exegesis/lib/Target.h
diff --git a/llvm/tools/llvm-exegesis/llvm-exegesis.cpp b/llvm/tools/llvm-exegesis/llvm-exegesis.cpp
