[lldb] [Process/FreeBSDRemote] Optimize regset pointer logic

Create a helper GetOffsetRegSetData() method to get pointer
to the regset data accounting for the necessary offset.  Establish
the offsets in the constructor and store them in the structure.  This
avoids having to add new Get*Offset() methods and combines some common
code.

Differential Revision: https://reviews.llvm.org/D91411

lldb/source/Plugins/Process/FreeBSDRemote/NativeRegisterContextFreeBSD_x86_64.cpp

@@ -262,8 +262,28 @@ CreateRegisterInfoInterface(const ArchSpec &target_arch) {
 NativeRegisterContextFreeBSD_x86_64::NativeRegisterContextFreeBSD_x86_64(
     const ArchSpec &target_arch, NativeThreadProtocol &native_thread)
     : NativeRegisterContextRegisterInfo(
-          native_thread, CreateRegisterInfoInterface(target_arch)) {
+          native_thread, CreateRegisterInfoInterface(target_arch)),
+      m_regset_offsets({0}) {
   assert(m_gpr.size() == GetRegisterInfoInterface().GetGPRSize());
+  std::array<uint32_t, MaxRegSet + 1> first_regnos;
+
+  switch (GetRegisterInfoInterface().GetTargetArchitecture().GetMachine()) {
+  case llvm::Triple::x86:
+    first_regnos[FPRegSet] = lldb_fctrl_i386;
+    first_regnos[DBRegSet] = lldb_dr0_i386;
+    break;
+  case llvm::Triple::x86_64:
+    first_regnos[FPRegSet] = lldb_fctrl_x86_64;
+    first_regnos[DBRegSet] = lldb_dr0_x86_64;
+    break;
+  default:
+    llvm_unreachable("Unhandled target architecture.");
+  }
+
+  for (int i: {FPRegSet, DBRegSet})
+    m_regset_offsets[i] = GetRegisterInfoInterface()
+                              .GetRegisterInfo()[first_regnos[i]]
+                              .byte_offset;
 }
 
 uint32_t NativeRegisterContextFreeBSD_x86_64::GetRegisterSetCount() const {
@@ -429,15 +449,9 @@ NativeRegisterContextFreeBSD_x86_64::ReadRegister(const RegisterInfo *reg_info,
 
   switch (set) {
   case GPRegSet:
-    reg_value.SetBytes(m_gpr.data() + reg_info->byte_offset,
-                       reg_info->byte_size, endian::InlHostByteOrder());
-    break;
   case FPRegSet:
-    reg_value.SetBytes(m_fpr.data() + reg_info->byte_offset - GetFPROffset(),
-                       reg_info->byte_size, endian::InlHostByteOrder());
-    break;
   case DBRegSet:
-    reg_value.SetBytes(m_dbr.data() + reg_info->byte_offset - GetDBROffset(),
+    reg_value.SetBytes(GetOffsetRegSetData(set, reg_info->byte_offset),
                        reg_info->byte_size, endian::InlHostByteOrder());
     break;
   case YMMRegSet: {
@@ -495,15 +509,9 @@ Status NativeRegisterContextFreeBSD_x86_64::WriteRegister(
 
   switch (set) {
   case GPRegSet:
-    ::memcpy(m_gpr.data() + reg_info->byte_offset, reg_value.GetBytes(),
-             reg_value.GetByteSize());
-    break;
   case FPRegSet:
-    ::memcpy(m_fpr.data() + reg_info->byte_offset - GetFPROffset(),
-             reg_value.GetBytes(), reg_value.GetByteSize());
-    break;
   case DBRegSet:
-    ::memcpy(m_dbr.data() + reg_info->byte_offset - GetDBROffset(),
+    ::memcpy(GetOffsetRegSetData(set, reg_info->byte_offset),
              reg_value.GetBytes(), reg_value.GetByteSize());
     break;
   case YMMRegSet: {
@@ -595,36 +603,25 @@ llvm::Error NativeRegisterContextFreeBSD_x86_64::CopyHardwareWatchpointsFrom(
   return res.ToError();
 }
 
-size_t NativeRegisterContextFreeBSD_x86_64::GetFPROffset() const {
+uint8_t *
-  uint32_t regno;
+NativeRegisterContextFreeBSD_x86_64::GetOffsetRegSetData(uint32_t set,
-  switch (GetRegisterInfoInterface().GetTargetArchitecture().GetMachine()) {
+                                                         size_t reg_offset) {
-  case llvm::Triple::x86:
+  uint8_t *base;
-    regno = lldb_fctrl_i386;
+  switch (set) {
+  case GPRegSet:
+    base = m_gpr.data();
     break;
-  case llvm::Triple::x86_64:
+  case FPRegSet:
-    regno = lldb_fctrl_x86_64;
+    base = m_fpr.data();
     break;
-  default:
+  case DBRegSet:
-    llvm_unreachable("Unhandled target architecture.");
+    base = m_dbr.data();
+    break;
+  case YMMRegSet:
+    llvm_unreachable("GetRegSetData() is unsuitable for this regset.");
   }
-
+  assert(reg_offset >= m_regset_offsets[set]);
-  return GetRegisterInfoInterface().GetRegisterInfo()[regno].byte_offset;
+  return base + (reg_offset - m_regset_offsets[set]);
-}
-
-size_t NativeRegisterContextFreeBSD_x86_64::GetDBROffset() const {
-  uint32_t regno;
-  switch (GetRegisterInfoInterface().GetTargetArchitecture().GetMachine()) {
-  case llvm::Triple::x86:
-    regno = lldb_dr0_i386;
-    break;
-  case llvm::Triple::x86_64:
-    regno = lldb_dr0_x86_64;
-    break;
-  default:
-    llvm_unreachable("Unhandled target architecture.");
-  }
-
-  return GetRegisterInfoInterface().GetRegisterInfo()[regno].byte_offset;
 }
 
 llvm::Optional<NativeRegisterContextFreeBSD_x86_64::YMMSplitPtr>

lldb/source/Plugins/Process/FreeBSDRemote/NativeRegisterContextFreeBSD_x86_64.h

@@ -72,14 +72,14 @@ private:
   std::array<uint8_t, sizeof(struct dbreg)> m_dbr;
   std::vector<uint8_t> m_xsave;
   std::array<uint32_t, MaxRegSet + 1> m_xsave_offsets;
+  std::array<size_t, MaxRegSet + 1> m_regset_offsets;
 
   llvm::Optional<enum RegSetKind> GetSetForNativeRegNum(int reg_num) const;
 
   Status ReadRegisterSet(uint32_t set);
   Status WriteRegisterSet(uint32_t set);
 
-  size_t GetFPROffset() const;
+  uint8_t *GetOffsetRegSetData(uint32_t set, size_t reg_offset);
-  size_t GetDBROffset() const;
 
   struct YMMSplitPtr {
     void *xmm;