[IR] Add getelementptr nusw and nuw flags (#90824)

This implements the `nusw` and `nuw` flags for `getelementptr` as
proposed at
https://discourse.llvm.org/t/rfc-add-nusw-and-nuw-flags-for-getelementptr/78672.

The three possible flags are encapsulated in the new `GEPNoWrapFlags`
class. Currently this class has a ctor from bool, interpreted as the
InBounds flag. This ctor should be removed in the future, as code gets
migrated to handle all flags.

There are a few places annotated with `TODO(gep_nowrap)`, where I've had
to touch code but opted to not infer or precisely preserve the new
flags, so as to keep this as NFC as possible and make sure any changes
of that kind get test coverage when they are made.

llvm/lib/Bitcode/Reader/BitcodeReader.cpp

@@ -1459,6 +1459,17 @@ unsigned BitcodeReader::getVirtualTypeID(Type *Ty,
   return TypeID;
 }
 
+static GEPNoWrapFlags toGEPNoWrapFlags(uint64_t Flags) {
+  GEPNoWrapFlags NW;
+  if (Flags & (1 << bitc::GEP_INBOUNDS))
+    NW |= GEPNoWrapFlags::inBounds();
+  if (Flags & (1 << bitc::GEP_NUSW))
+    NW |= GEPNoWrapFlags::noUnsignedSignedWrap();
+  if (Flags & (1 << bitc::GEP_NUW))
+    NW |= GEPNoWrapFlags::noUnsignedWrap();
+  return NW;
+}
+
 static bool isConstExprSupported(const BitcodeConstant *BC) {
   uint8_t Opcode = BC->Opcode;
 
@@ -1614,9 +1625,9 @@ Expected<Value *> BitcodeReader::materializeValue(unsigned StartValID,
           C = ConstantExpr::getCompare(BC->Flags, ConstOps[0], ConstOps[1]);
           break;
         case Instruction::GetElementPtr:
-          C = ConstantExpr::getGetElementPtr(BC->SrcElemTy, ConstOps[0],
-                                             ArrayRef(ConstOps).drop_front(),
-                                             BC->Flags, BC->getInRange());
+          C = ConstantExpr::getGetElementPtr(
+              BC->SrcElemTy, ConstOps[0], ArrayRef(ConstOps).drop_front(),
+              toGEPNoWrapFlags(BC->Flags), BC->getInRange());
           break;
         case Instruction::ExtractElement:
           C = ConstantExpr::getExtractElement(ConstOps[0], ConstOps[1]);
@@ -1700,8 +1711,7 @@ Expected<Value *> BitcodeReader::materializeValue(unsigned StartValID,
         I = GetElementPtrInst::Create(BC->SrcElemTy, Ops[0],
                                       ArrayRef(Ops).drop_front(), "constexpr",
                                       InsertBB);
-        if (BC->Flags)
-          cast<GetElementPtrInst>(I)->setIsInBounds();
+        cast<GetElementPtrInst>(I)->setNoWrapFlags(toGEPNoWrapFlags(BC->Flags));
         break;
       case Instruction::Select:
         I = SelectInst::Create(Ops[0], Ops[1], Ops[2], "constexpr", InsertBB);
@@ -3321,9 +3331,10 @@ Error BitcodeReader::parseConstants() {
       break;
     }
     case bitc::CST_CODE_CE_INBOUNDS_GEP: // [ty, n x operands]
-    case bitc::CST_CODE_CE_GEP: // [ty, n x operands]
+    case bitc::CST_CODE_CE_GEP_OLD:      // [ty, n x operands]
     case bitc::CST_CODE_CE_GEP_WITH_INRANGE_INDEX_OLD: // [ty, flags, n x
                                                        // operands]
+    case bitc::CST_CODE_CE_GEP:                // [ty, flags, n x operands]
     case bitc::CST_CODE_CE_GEP_WITH_INRANGE: { // [ty, flags, start, end, n x
                                                // operands]
       if (Record.size() < 2)
@@ -3331,27 +3342,29 @@ Error BitcodeReader::parseConstants() {
       unsigned OpNum = 0;
       Type *PointeeType = nullptr;
       if (BitCode == bitc::CST_CODE_CE_GEP_WITH_INRANGE_INDEX_OLD ||
-          BitCode == bitc::CST_CODE_CE_GEP_WITH_INRANGE || Record.size() % 2)
+          BitCode == bitc::CST_CODE_CE_GEP_WITH_INRANGE ||
+          BitCode == bitc::CST_CODE_CE_GEP || Record.size() % 2)
         PointeeType = getTypeByID(Record[OpNum++]);
 
-      bool InBounds = false;
+      uint64_t Flags = 0;
       std::optional<ConstantRange> InRange;
       if (BitCode == bitc::CST_CODE_CE_GEP_WITH_INRANGE_INDEX_OLD) {
         uint64_t Op = Record[OpNum++];
-        InBounds = Op & 1;
+        Flags = Op & 1; // inbounds
         unsigned InRangeIndex = Op >> 1;
         // "Upgrade" inrange by dropping it. The feature is too niche to
         // bother.
         (void)InRangeIndex;
       } else if (BitCode == bitc::CST_CODE_CE_GEP_WITH_INRANGE) {
-        uint64_t Op = Record[OpNum++];
-        InBounds = Op & 1;
+        Flags = Record[OpNum++];
         Expected<ConstantRange> MaybeInRange = readConstantRange(Record, OpNum);
         if (!MaybeInRange)
           return MaybeInRange.takeError();
         InRange = MaybeInRange.get();
+      } else if (BitCode == bitc::CST_CODE_CE_GEP) {
+        Flags = Record[OpNum++];
       } else if (BitCode == bitc::CST_CODE_CE_INBOUNDS_GEP)
-        InBounds = true;
+        Flags = (1 << bitc::GEP_INBOUNDS);
 
       SmallVector<unsigned, 16> Elts;
       unsigned BaseTypeID = Record[OpNum];
@@ -3384,7 +3397,8 @@ Error BitcodeReader::parseConstants() {
 
       V = BitcodeConstant::create(
           Alloc, CurTy,
-          {Instruction::GetElementPtr, InBounds, PointeeType, InRange}, Elts);
+          {Instruction::GetElementPtr, uint8_t(Flags), PointeeType, InRange},
+          Elts);
       break;
     }
     case bitc::CST_CODE_CE_SELECT: {  // CE_SELECT: [opval#, opval#, opval#]
@@ -5062,14 +5076,15 @@ Error BitcodeReader::parseFunctionBody(Function *F) {
 
       unsigned TyID;
       Type *Ty;
-      bool InBounds;
+      GEPNoWrapFlags NW;
 
       if (BitCode == bitc::FUNC_CODE_INST_GEP) {
-        InBounds = Record[OpNum++];
+        NW = toGEPNoWrapFlags(Record[OpNum++]);
         TyID = Record[OpNum++];
         Ty = getTypeByID(TyID);
       } else {
-        InBounds = BitCode == bitc::FUNC_CODE_INST_INBOUNDS_GEP_OLD;
+        if (BitCode == bitc::FUNC_CODE_INST_INBOUNDS_GEP_OLD)
+          NW = GEPNoWrapFlags::inBounds();
         TyID = InvalidTypeID;
         Ty = nullptr;
       }
@@ -5096,7 +5111,8 @@ Error BitcodeReader::parseFunctionBody(Function *F) {
         GEPIdx.push_back(Op);
       }
 
-      I = GetElementPtrInst::Create(Ty, BasePtr, GEPIdx);
+      auto *GEP = GetElementPtrInst::Create(Ty, BasePtr, GEPIdx);
+      I = GEP;
 
       ResTypeID = TyID;
       if (cast<GEPOperator>(I)->getNumIndices() != 0) {
@@ -5122,8 +5138,7 @@ Error BitcodeReader::parseFunctionBody(Function *F) {
         ResTypeID = getVirtualTypeID(I->getType(), ResTypeID);
 
       InstructionList.push_back(I);
-      if (InBounds)
-        cast<GetElementPtrInst>(I)->setIsInBounds(true);
+      GEP->setNoWrapFlags(NW);
       break;
     }