diff --git a/lib/Support/APFloat.cpp b/lib/Support/APFloat.cpp
index 3c76c72271..d846b248d4 100644
--- a/lib/Support/APFloat.cpp
+++ b/lib/Support/APFloat.cpp
@@ -446,7 +446,7 @@ ulpsFromBoundary(const integerPart *parts, unsigned int bits, bool isNearest)
       if (~parts[count])
         return ~(integerPart) 0; /* A lot.  */
 
-    return -parts[0];
+    return (~parts[0] + 1);
   }
 
   return ~(integerPart) 0; /* A lot.  */
diff --git a/lib/Support/StringRef.cpp b/lib/Support/StringRef.cpp
index ddece087a9..52b949d826 100644
--- a/lib/Support/StringRef.cpp
+++ b/lib/Support/StringRef.cpp
@@ -12,6 +12,7 @@
 #include "llvm/ADT/Hashing.h"
 #include "llvm/ADT/edit_distance.h"
 #include <bitset>
+#include <limits>
 
 using namespace llvm;
 
@@ -393,13 +394,16 @@ bool llvm::getAsSignedInteger(StringRef Str, unsigned Radix,
 
   // Get the positive part of the value.
   if (getAsUnsignedInteger(Str.substr(1), Radix, ULLVal) ||
-      // Reject values so large they'd overflow as negative signed, but allow
-      // "-0".  This negates the unsigned so that the negative isn't undefined
-      // on signed overflow.
-      (long long)-ULLVal > 0)
+      // Reject values larger than what can be represented as negative signed.
+      // The most negative long long is LLONG_MIN, which has magnitude
+      // (LLONG_MAX + 1). Values larger than this magnitude cannot be negated
+      // without overflow.
+      ULLVal > static_cast<unsigned long long>(
+                   std::numeric_limits<long long>::max()) +
+                   1)
     return true;
 
-  Result = -ULLVal;
+  Result = (~ULLVal + 1);
   return false;
 }
 
diff --git a/lib/Support/TimeValue.cpp b/lib/Support/TimeValue.cpp
index 136b93ecee..06de27bbda 100644
--- a/lib/Support/TimeValue.cpp
+++ b/lib/Support/TimeValue.cpp
@@ -19,8 +19,7 @@ using namespace sys;
 
 const TimeValue::SecondsType
   TimeValue::PosixZeroTimeSeconds = -946684800;
-const TimeValue::SecondsType
-  TimeValue::Win32ZeroTimeSeconds = -12591158400ULL;
+const TimeValue::SecondsType TimeValue::Win32ZeroTimeSeconds = -12591158400LL;
 
 void
 TimeValue::normalize( void ) {
diff --git a/lib/Transforms/Scalar/LoopStrengthReduce.cpp b/lib/Transforms/Scalar/LoopStrengthReduce.cpp
index 3ab9367a6b..60962ec69a 100644
--- a/lib/Transforms/Scalar/LoopStrengthReduce.cpp
+++ b/lib/Transforms/Scalar/LoopStrengthReduce.cpp
@@ -1395,8 +1395,11 @@ static bool isAMCompletelyFolded(const TargetTransformInfo &TTI,
       // ICmpZero -1*ScaleReg + BaseOffset => ICmp ScaleReg, BaseOffset
       // Offs is the ICmp immediate.
       if (Scale == 0)
-        // The cast does the right thing with INT64_MIN.
-        BaseOffset = -(uint64_t)BaseOffset;
+        // Negate BaseOffset using two's complement (~x + 1) to avoid undefined
+        // behavior. Simple negation (-BaseOffset) would be undefined for
+        // INT64_MIN since -INT64_MIN cannot fit in int64_t. Two's complement
+        // gives the expected wraparound behavior: -INT64_MIN becomes INT64_MIN.
+        BaseOffset = ~BaseOffset + 1ULL;
       return TTI.isLegalICmpImmediate(BaseOffset);
     }
 
@@ -3000,7 +3003,7 @@ void LSRInstance::CollectFixupsAndInitialFormulae() {
         // of -1) are now also interesting.
         for (size_t i = 0, e = Factors.size(); i != e; ++i)
           if (Factors[i] != -1)
-            Factors.insert(-(uint64_t)Factors[i]);
+            Factors.insert(~Factors[i] + 1ULL);
         Factors.insert(-1);
       }
 
@@ -3739,7 +3742,7 @@ void LSRInstance::GenerateCrossUseConstantOffsets() {
     const SCEV *OrigReg = WI.OrigReg;
 
     Type *IntTy = SE.getEffectiveSCEVType(OrigReg->getType());
-    const SCEV *NegImmS = SE.getSCEV(ConstantInt::get(IntTy, -(uint64_t)Imm));
+    const SCEV *NegImmS = SE.getSCEV(ConstantInt::get(IntTy, ~Imm + 1ULL));
     unsigned BitWidth = SE.getTypeSizeInBits(IntTy);
 
     // TODO: Use a more targeted data structure.
@@ -3754,8 +3757,8 @@ void LSRInstance::GenerateCrossUseConstantOffsets() {
       if (F.ScaledReg == OrigReg) {
         int64_t Offset = (uint64_t)F.BaseOffset + Imm * (uint64_t)F.Scale;
         // Don't create 50 + reg(-50).
-        if (F.referencesReg(SE.getSCEV(
-                   ConstantInt::get(IntTy, -(uint64_t)Offset))))
+        if (F.referencesReg(
+                SE.getSCEV(ConstantInt::get(IntTy, ~Offset + 1ULL))))
           continue;
         Formula NewF = F;
         NewF.BaseOffset = Offset;
@@ -4556,7 +4559,7 @@ Value *LSRInstance::Expand(const LSRFixup &LF, const Formula &F,
       // The other interesting way of "folding" with an ICmpZero is to use a
       // negated immediate.
       if (!ICmpScaledV)
-        ICmpScaledV = ConstantInt::get(IntTy, -(uint64_t)Offset);
+        ICmpScaledV = ConstantInt::get(IntTy, ~Offset + 1ULL);
       else {
         Ops.push_back(SE.getUnknown(ICmpScaledV));
         ICmpScaledV = ConstantInt::get(IntTy, Offset);
@@ -4608,8 +4611,8 @@ Value *LSRInstance::Expand(const LSRFixup &LF, const Formula &F,
       assert((F.Scale == 0 || F.Scale == 1) &&
              "ICmp does not support folding a global value and "
              "a scale at the same time!");
-      Constant *C = ConstantInt::getSigned(SE.getEffectiveSCEVType(OpTy),
-                                           -(uint64_t)Offset);
+      Constant *C =
+          ConstantInt::getSigned(SE.getEffectiveSCEVType(OpTy), ~Offset + 1ULL);
       if (C->getType() != OpTy)
         C = ConstantExpr::getCast(CastInst::getCastOpcode(C, false,
                                                           OpTy, false),
diff --git a/tools/clang/lib/AST/ExprConstant.cpp b/tools/clang/lib/AST/ExprConstant.cpp
index 69e0760bce..9336a80e05 100644
--- a/tools/clang/lib/AST/ExprConstant.cpp
+++ b/tools/clang/lib/AST/ExprConstant.cpp
@@ -6558,7 +6558,7 @@ bool IntExprEvaluator::VisitCallExpr(const CallExpr *E) {
     // handle all cases where the expression has side-effects.
     if (E->getArg(0)->HasSideEffects(Info.Ctx)) {
       if (E->getArg(1)->EvaluateKnownConstInt(Info.Ctx).getZExtValue() <= 1)
-        return Success(-1ULL, E);
+        return Success(~0ULL, E);
       return Success(0, E);
     }
 
@@ -6573,7 +6573,7 @@ bool IntExprEvaluator::VisitCallExpr(const CallExpr *E) {
       return Error(E);
     case EvalInfo::EM_ConstantExpressionUnevaluated:
     case EvalInfo::EM_PotentialConstantExpressionUnevaluated:
-      return Success(-1ULL, E);
+      return Success(~0ULL, E);
     }
     llvm_unreachable("Invalid EvalMode!");
   }
diff --git a/tools/clang/lib/AST/MicrosoftMangle.cpp b/tools/clang/lib/AST/MicrosoftMangle.cpp
index 40dca1bb1b..ae9f1cd7f8 100644
--- a/tools/clang/lib/AST/MicrosoftMangle.cpp
+++ b/tools/clang/lib/AST/MicrosoftMangle.cpp
@@ -633,7 +633,7 @@ void MicrosoftCXXNameMangler::mangleNumber(int64_t Number) {
 
   uint64_t Value = static_cast<uint64_t>(Number);
   if (Number < 0) {
-    Value = -Value;
+    Value = ~Value + 1ULL;
     Out << '?';
   }
 
@@ -2308,7 +2308,7 @@ static void mangleThunkThisAdjustment(const CXXMethodDecl *MD,
       Out << AccessSpec;
       Mangler.mangleNumber(
           static_cast<uint32_t>(Adjustment.Virtual.Microsoft.VtordispOffset));
-      Mangler.mangleNumber(-static_cast<uint32_t>(Adjustment.NonVirtual));
+      Mangler.mangleNumber(~static_cast<uint32_t>(Adjustment.NonVirtual) + 1);
     }
   } else if (Adjustment.NonVirtual != 0) {
     switch (MD->getAccess()) {
@@ -2323,7 +2323,7 @@ static void mangleThunkThisAdjustment(const CXXMethodDecl *MD,
     case AS_public:
       Out << 'W';
     }
-    Mangler.mangleNumber(-static_cast<uint32_t>(Adjustment.NonVirtual));
+    Mangler.mangleNumber(~static_cast<uint32_t>(Adjustment.NonVirtual) + 1);
   } else {
     switch (MD->getAccess()) {
     case AS_none:
diff --git a/tools/clang/lib/CodeGen/CoverageMappingGen.cpp b/tools/clang/lib/CodeGen/CoverageMappingGen.cpp
index eca91590e6..e16e015a74 100644
--- a/tools/clang/lib/CodeGen/CoverageMappingGen.cpp
+++ b/tools/clang/lib/CodeGen/CoverageMappingGen.cpp
@@ -116,7 +116,7 @@ class CoverageMappingBuilder {
   /// \brief Return the start location of an included file or expanded macro.
   SourceLocation getStartOfFileOrMacro(SourceLocation Loc) {
     if (Loc.isMacroID())
-      return Loc.getLocWithOffset(-SM.getFileOffset(Loc));
+      return Loc.getLocWithOffset(~SM.getFileOffset(Loc) + 1);
     return SM.getLocForStartOfFile(SM.getFileID(Loc));
   }
 
diff --git a/tools/clang/lib/CodeGen/ItaniumCXXABI.cpp b/tools/clang/lib/CodeGen/ItaniumCXXABI.cpp
index 97fe28be7f..698d34c774 100644
--- a/tools/clang/lib/CodeGen/ItaniumCXXABI.cpp
+++ b/tools/clang/lib/CodeGen/ItaniumCXXABI.cpp
@@ -639,8 +639,8 @@ llvm::Constant *
 ItaniumCXXABI::EmitNullMemberPointer(const MemberPointerType *MPT) {
   // Itanium C++ ABI 2.3:
   //   A NULL pointer is represented as -1.
-  if (MPT->isMemberDataPointer()) 
-    return llvm::ConstantInt::get(CGM.PtrDiffTy, -1ULL, /*isSigned=*/true);
+  if (MPT->isMemberDataPointer())
+    return llvm::ConstantInt::get(CGM.PtrDiffTy, -1LL, /*isSigned=*/true);
 
   llvm::Constant *Zero = llvm::ConstantInt::get(CGM.PtrDiffTy, 0);
   llvm::Constant *Values[2] = { Zero, Zero };
@@ -1023,7 +1023,7 @@ static CharUnits computeOffsetHint(ASTContext &Context,
   // If Dst is not derived from Src we can skip the whole computation below and
   // return that Src is not a public base of Dst.  Record all inheritance paths.
   if (!Dst->isDerivedFrom(Src, Paths))
-    return CharUnits::fromQuantity(-2ULL);
+    return CharUnits::fromQuantity(-2LL);
 
   unsigned NumPublicPaths = 0;
   CharUnits Offset;
@@ -1040,7 +1040,7 @@ static CharUnits computeOffsetHint(ASTContext &Context,
       // If the path contains a virtual base class we can't give any hint.
       // -1: no hint.
       if (J->Base->isVirtual())
-        return CharUnits::fromQuantity(-1ULL);
+        return CharUnits::fromQuantity(-1LL);
 
       if (NumPublicPaths > 1) // Won't use offsets, skip computation.
         continue;
@@ -1053,11 +1053,11 @@ static CharUnits computeOffsetHint(ASTContext &Context,
 
   // -2: Src is not a public base of Dst.
   if (NumPublicPaths == 0)
-    return CharUnits::fromQuantity(-2ULL);
+    return CharUnits::fromQuantity(-2LL);
 
   // -3: Src is a multiple public base type but never a virtual base type.
   if (NumPublicPaths > 1)
-    return CharUnits::fromQuantity(-3ULL);
+    return CharUnits::fromQuantity(-3LL);
 
   // Otherwise, the Src type is a unique public nonvirtual base type of Dst.
   // Return the offset of Src from the origin of Dst.
@@ -1154,7 +1154,7 @@ llvm::Value *ItaniumCXXABI::EmitDynamicCastToVoid(CodeGenFunction &CGF,
 
   // Get the offset-to-top from the vtable.
   llvm::Value *OffsetToTop =
-      CGF.Builder.CreateConstInBoundsGEP1_64(VTable, -2ULL);
+      CGF.Builder.CreateConstInBoundsGEP1_64(VTable, -2LL);
   OffsetToTop = CGF.Builder.CreateLoad(OffsetToTop, "offset.to.top");
 
   // Finally, add the offset to the pointer.
diff --git a/tools/clang/lib/CodeGen/TargetInfo.cpp b/tools/clang/lib/CodeGen/TargetInfo.cpp
index aba43964d9..aaf63355af 100644
--- a/tools/clang/lib/CodeGen/TargetInfo.cpp
+++ b/tools/clang/lib/CodeGen/TargetInfo.cpp
@@ -1283,7 +1283,7 @@ llvm::Value *X86_32ABIInfo::EmitVAArg(llvm::Value *VAListAddr, QualType Ty,
     Addr = CGF.Builder.CreateGEP(Addr, Offset);
     llvm::Value *AsInt = CGF.Builder.CreatePtrToInt(Addr,
                                                     CGF.Int32Ty);
-    llvm::Value *Mask = llvm::ConstantInt::get(CGF.Int32Ty, -Align);
+    llvm::Value *Mask = llvm::ConstantInt::get(CGF.Int32Ty, ~Align + 1);
     Addr = CGF.Builder.CreateIntToPtr(CGF.Builder.CreateAnd(AsInt, Mask),
                                       Addr->getType(),
                                       "ap.cur.aligned");
@@ -2849,7 +2849,7 @@ static llvm::Value *EmitVAArgFromMemory(llvm::Value *VAListAddr,
     overflow_arg_area = CGF.Builder.CreateGEP(overflow_arg_area, Offset);
     llvm::Value *AsInt = CGF.Builder.CreatePtrToInt(overflow_arg_area,
                                                     CGF.Int64Ty);
-    llvm::Value *Mask = llvm::ConstantInt::get(CGF.Int64Ty, -(uint64_t)Align);
+    llvm::Value *Mask = llvm::ConstantInt::get(CGF.Int64Ty, ~Align + 1);
     overflow_arg_area =
       CGF.Builder.CreateIntToPtr(CGF.Builder.CreateAnd(AsInt, Mask),
                                  overflow_arg_area->getType(),
diff --git a/tools/clang/lib/Format/Format.cpp b/tools/clang/lib/Format/Format.cpp
index 7d556c9f0f..b6ca328972 100644
--- a/tools/clang/lib/Format/Format.cpp
+++ b/tools/clang/lib/Format/Format.cpp
@@ -1049,7 +1049,7 @@ class FormatTokenLexer {
     FormatTok = new (Allocator.Allocate()) FormatToken;
     readRawToken(*FormatTok);
     SourceLocation WhitespaceStart =
-        FormatTok->Tok.getLocation().getLocWithOffset(-TrailingWhitespace);
+        FormatTok->Tok.getLocation().getLocWithOffset(~TrailingWhitespace + 1);
     FormatTok->IsFirst = IsFirstToken;
     IsFirstToken = false;
 
diff --git a/tools/clang/lib/Lex/Lexer.cpp b/tools/clang/lib/Lex/Lexer.cpp
index 089e76b78b..aa72980e2f 100644
--- a/tools/clang/lib/Lex/Lexer.cpp
+++ b/tools/clang/lib/Lex/Lexer.cpp
@@ -480,7 +480,7 @@ static SourceLocation getBeginningOfFileToken(SourceLocation Loc,
   }
   
   // Create a lexer starting at the beginning of this token.
-  SourceLocation LexerStartLoc = Loc.getLocWithOffset(-LocInfo.second);
+  SourceLocation LexerStartLoc = Loc.getLocWithOffset(~LocInfo.second + 1);
   Lexer TheLexer(LexerStartLoc, LangOpts, BufStart, LexStart, Buffer.end());
   TheLexer.SetCommentRetentionState(true);
   
diff --git a/tools/clang/lib/Rewrite/Rewriter.cpp b/tools/clang/lib/Rewrite/Rewriter.cpp
index be09a363a6..fa081d65ac 100644
--- a/tools/clang/lib/Rewrite/Rewriter.cpp
+++ b/tools/clang/lib/Rewrite/Rewriter.cpp
@@ -60,7 +60,7 @@ void RewriteBuffer::RemoveText(unsigned OrigOffset, unsigned Size,
   Buffer.erase(RealOffset, Size);
 
   // Add a delta so that future changes are offset correctly.
-  AddReplaceDelta(OrigOffset, -Size);
+  AddReplaceDelta(OrigOffset, ~Size + 1);
 
   if (removeLineIfEmpty) {
     // Find the line that the remove occurred and if it is completely empty
@@ -86,7 +86,7 @@ void RewriteBuffer::RemoveText(unsigned OrigOffset, unsigned Size,
     }
     if (posI != end() && *posI == '\n') {
       Buffer.erase(curLineStartOffs, lineSize + 1/* + '\n'*/);
-      AddReplaceDelta(curLineStartOffs, -(lineSize + 1/* + '\n'*/));
+      AddReplaceDelta(curLineStartOffs, ~(lineSize + 1 /* + '\n'*/) + 1);
     }
   }
 }