Add TRI::getSubRegIndexLaneMask().

Sub-register lane masks are bitmasks that can be used to determine if
two sub-registers of a virtual register will overlap. For example, ARM's
ssub0 and ssub1 sub-register indices don't overlap each other, but both
overlap dsub0 and qsub0.

The lane masks will be accurate on most targets, but on targets that use
sub-register indexes in an irregular way, the masks may conservatively
report that two sub-register indices overlap when the eventually
allocated physregs don't.

Irregular register banks also mean that the bits in a lane mask can't be
mapped onto register units, but the concept is similar.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@163630 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/Target/TargetRegisterInfo.h

@@ -221,13 +221,17 @@ public:
 private:
   const TargetRegisterInfoDesc *InfoDesc;     // Extra desc array for codegen
   const char *const *SubRegIndexNames;        // Names of subreg indexes.
+  // Pointer to array of lane masks, one per sub-reg index.
+  const unsigned *SubRegIndexLaneMasks;
+
   regclass_iterator RegClassBegin, RegClassEnd;   // List of regclasses
 
 protected:
   TargetRegisterInfo(const TargetRegisterInfoDesc *ID,
                      regclass_iterator RegClassBegin,
                      regclass_iterator RegClassEnd,
-                     const char *const *subregindexnames);
+                     const char *const *SRINames,
+                     const unsigned *SRILaneMasks);
   virtual ~TargetRegisterInfo();
 public:
 
@@ -332,6 +336,31 @@ public:
     return SubRegIndexNames[SubIdx-1];
   }
 
+  /// getSubRegIndexLaneMask - Return a bitmask representing the parts of a
+  /// register that are covered by SubIdx.
+  ///
+  /// Lane masks for sub-register indices are similar to register units for
+  /// physical registers. The individual bits in a lane mask can't be assigned
+  /// any specific meaning. They can be used to check if two sub-register
+  /// indices overlap.
+  ///
+  /// If the target has a register such that:
+  ///
+  ///   getSubReg(Reg, A) overlaps getSubReg(Reg, B)
+  ///
+  /// then:
+  ///
+  ///   getSubRegIndexLaneMask(A) & getSubRegIndexLaneMask(B) != 0
+  ///
+  /// The converse is not necessarily true. If two lane masks have a common
+  /// bit, the corresponding sub-registers may not overlap, but it can be
+  /// assumed that they usually will.
+  unsigned getSubRegIndexLaneMask(unsigned SubIdx) const {
+    // SubIdx == 0 is allowed, it has the lane mask ~0u.
+    assert(SubIdx < getNumSubRegIndices() && "This is not a subregister index");
+    return SubRegIndexLaneMasks[SubIdx];
+  }
+
   /// regsOverlap - Returns true if the two registers are equal or alias each
   /// other. The registers may be virtual register.
   bool regsOverlap(unsigned regA, unsigned regB) const {

lib/Target/TargetRegisterInfo.cpp

@@ -20,8 +20,10 @@ using namespace llvm;
 
 TargetRegisterInfo::TargetRegisterInfo(const TargetRegisterInfoDesc *ID,
                              regclass_iterator RCB, regclass_iterator RCE,
-                             const char *const *subregindexnames)
-  : InfoDesc(ID), SubRegIndexNames(subregindexnames),
+                             const char *const *SRINames,
+                             const unsigned *SRILaneMasks)
+  : InfoDesc(ID), SubRegIndexNames(SRINames),
+    SubRegIndexLaneMasks(SRILaneMasks),
     RegClassBegin(RCB), RegClassEnd(RCE) {
 }
 

utils/TableGen/CodeGenRegisters.cpp

@@ -28,7 +28,7 @@ using namespace llvm;
 //===----------------------------------------------------------------------===//
 
 CodeGenSubRegIndex::CodeGenSubRegIndex(Record *R, unsigned Enum)
-  : TheDef(R), EnumValue(Enum) {
+  : TheDef(R), EnumValue(Enum), LaneMask(0) {
   Name = R->getName();
   if (R->getValue("Namespace"))
     Namespace = R->getValueAsString("Namespace");
@@ -36,7 +36,7 @@ CodeGenSubRegIndex::CodeGenSubRegIndex(Record *R, unsigned Enum)
 
 CodeGenSubRegIndex::CodeGenSubRegIndex(StringRef N, StringRef Nspace,
                                        unsigned Enum)
-  : TheDef(0), Name(N), Namespace(Nspace), EnumValue(Enum) {
+  : TheDef(0), Name(N), Namespace(Nspace), EnumValue(Enum), LaneMask(0) {
 }
 
 std::string CodeGenSubRegIndex::getQualifiedName() const {
@@ -75,6 +75,23 @@ void CodeGenSubRegIndex::updateComponents(CodeGenRegBank &RegBank) {
   }
 }
 
+unsigned CodeGenSubRegIndex::computeLaneMask() {
+  // Already computed?
+  if (LaneMask)
+    return LaneMask;
+
+  // Recursion guard, shouldn't be required.
+  LaneMask = ~0u;
+
+  // The lane mask is simply the union of all sub-indices.
+  unsigned M = 0;
+  for (CompMap::iterator I = Composed.begin(), E = Composed.end(); I != E; ++I)
+    M |= I->second->computeLaneMask();
+  assert(M && "Missing lane mask, sub-register cycle?");
+  LaneMask = M;
+  return LaneMask;
+}
+
 //===----------------------------------------------------------------------===//
 //                              CodeGenRegister
 //===----------------------------------------------------------------------===//
@@ -1156,6 +1173,35 @@ void CodeGenRegBank::computeComposites() {
   }
 }
 
+// Compute lane masks. This is similar to register units, but at the
+// sub-register index level. Each bit in the lane mask is like a register unit
+// class, and two lane masks will have a bit in common if two sub-register
+// indices overlap in some register.
+//
+// Conservatively share a lane mask bit if two sub-register indices overlap in
+// some registers, but not in others. That shouldn't happen a lot.
+void CodeGenRegBank::computeSubRegIndexLaneMasks() {
+  // First assign individual bits to all the leaf indices.
+  unsigned Bit = 0;
+  for (unsigned i = 0, e = SubRegIndices.size(); i != e; ++i) {
+    CodeGenSubRegIndex *Idx = SubRegIndices[i];
+    if (Idx->getComposites().empty()) {
+      Idx->LaneMask = 1u << Bit;
+      // Share bit 31 in the unlikely case there are more than 32 leafs.
+      if (Bit < 31) ++Bit;
+    } else {
+      Idx->LaneMask = 0;
+    }
+  }
+
+  // FIXME: What if ad-hoc aliasing introduces overlaps that aren't represented
+  // by the sub-register graph? This doesn't occur in any known targets.
+
+  // Inherit lanes from composites.
+  for (unsigned i = 0, e = SubRegIndices.size(); i != e; ++i)
+    SubRegIndices[i]->computeLaneMask();
+}
+
 namespace {
 // UberRegSet is a helper class for computeRegUnitWeights. Each UberRegSet is
 // the transitive closure of the union of overlapping register
@@ -1539,6 +1585,7 @@ void CodeGenRegBank::computeRegUnitSets() {
 
 void CodeGenRegBank::computeDerivedInfo() {
   computeComposites();
+  computeSubRegIndexLaneMasks();
 
   // Compute a weight for each register unit created during getSubRegs.
   // This may create adopted register units (with unit # >= NumNativeRegUnits).

utils/TableGen/CodeGenRegisters.h

@@ -40,6 +40,7 @@ namespace llvm {
 
   public:
     const unsigned EnumValue;
+    unsigned LaneMask;
 
     CodeGenSubRegIndex(Record *R, unsigned Enum);
     CodeGenSubRegIndex(StringRef N, StringRef Nspace, unsigned Enum);
@@ -83,6 +84,9 @@ namespace llvm {
     // Return the map of composites.
     const CompMap &getComposites() const { return Composed; }
 
+    // Compute LaneMask from Composed. Return LaneMask.
+    unsigned computeLaneMask();
+
   private:
     CompMap Composed;
   };
@@ -486,6 +490,9 @@ namespace llvm {
     // Populate the Composite map from sub-register relationships.
     void computeComposites();
 
+    // Compute a lane mask for each sub-register index.
+    void computeSubRegIndexLaneMasks();
+
   public:
     CodeGenRegBank(RecordKeeper&);
 

utils/TableGen/RegisterInfoEmitter.cpp

@@ -876,15 +876,23 @@ RegisterInfoEmitter::runTargetDesc(raw_ostream &OS, CodeGenTarget &Target,
   VTSeqs.emit(OS, printSimpleValueType, "MVT::Other");
   OS << "};\n";
 
-  // Emit SubRegIndex names, skipping 0
-  OS << "\nstatic const char *const SubRegIndexTable[] = { \"";
+  // Emit SubRegIndex names, skipping 0.
+  OS << "\nstatic const char *const SubRegIndexNameTable[] = { \"";
   for (unsigned i = 0, e = SubRegIndices.size(); i != e; ++i) {
     OS << SubRegIndices[i]->getName();
-    if (i+1 != e)
+    if (i + 1 != e)
       OS << "\", \"";
   }
   OS << "\" };\n\n";
 
+  // Emit SubRegIndex lane masks, including 0.
+  OS << "\nstatic const unsigned SubRegIndexLaneMaskTable[] = {\n  ~0u,\n";
+  for (unsigned i = 0, e = SubRegIndices.size(); i != e; ++i) {
+    OS << format("  0x%08x, // ", SubRegIndices[i]->LaneMask)
+       << SubRegIndices[i]->getName() << '\n';
+  }
+  OS << " };\n\n";
+
   OS << "\n";
 
   // Now that all of the structs have been emitted, emit the instances.
@@ -1122,7 +1130,7 @@ RegisterInfoEmitter::runTargetDesc(raw_ostream &OS, CodeGenTarget &Target,
      << "(unsigned RA, unsigned DwarfFlavour, unsigned EHFlavour)\n"
      << "  : TargetRegisterInfo(" << TargetName << "RegInfoDesc"
      << ", RegisterClasses, RegisterClasses+" << RegisterClasses.size() <<",\n"
-     << "             SubRegIndexTable) {\n"
+     << "             SubRegIndexNameTable, SubRegIndexLaneMaskTable) {\n"
      << "  InitMCRegisterInfo(" << TargetName << "RegDesc, "
      << Regs.size()+1 << ", RA,\n                     " << TargetName
      << "MCRegisterClasses, " << RegisterClasses.size() << ",\n"