1 files changed, 95 insertions, 0 deletions
diff --git a/clang/lib/CodeGen/CGBuiltin.cpp b/clang/lib/CodeGen/CGBuiltin.cpp
index cb052ebcacc..7d59d55a25b 100644
--- a/clang/lib/CodeGen/CGBuiltin.cpp
+++ b/clang/lib/CodeGen/CGBuiltin.cpp
@@ -839,6 +839,93 @@ RValue CodeGenFunction::emitBuiltinOSLogFormat(const CallExpr &E) {
   return RValue::get(BufAddr.getPointer());
 }
 
+/// Determine if a binop is a checked mixed-sign multiply we can specialize.
+static bool isSpecialMixedSignMultiply(unsigned BuiltinID,
+                                       WidthAndSignedness Op1Info,
+                                       WidthAndSignedness Op2Info,
+                                       WidthAndSignedness ResultInfo) {
+  return BuiltinID == Builtin::BI__builtin_mul_overflow &&
+         Op1Info.Width == Op2Info.Width && Op1Info.Width >= ResultInfo.Width &&
+         Op1Info.Signed != Op2Info.Signed;
+}
+
+/// Emit a checked mixed-sign multiply. This is a cheaper specialization of
+/// the generic checked-binop irgen.
+static RValue
+EmitCheckedMixedSignMultiply(CodeGenFunction &CGF, const clang::Expr *Op1,
+                             WidthAndSignedness Op1Info, const clang::Expr *Op2,
+                             WidthAndSignedness Op2Info,
+                             const clang::Expr *ResultArg, QualType ResultQTy,
+                             WidthAndSignedness ResultInfo) {
+  assert(isSpecialMixedSignMultiply(Builtin::BI__builtin_mul_overflow, Op1Info,
+                                    Op2Info, ResultInfo) &&
+         "Not a mixed-sign multipliction we can specialize");
+
+  // Emit the signed and unsigned operands.
+  const clang::Expr *SignedOp = Op1Info.Signed ? Op1 : Op2;
+  const clang::Expr *UnsignedOp = Op1Info.Signed ? Op2 : Op1;
+  llvm::Value *Signed = CGF.EmitScalarExpr(SignedOp);
+  llvm::Value *Unsigned = CGF.EmitScalarExpr(UnsignedOp);
+
+  llvm::Type *OpTy = Signed->getType();
+  llvm::Value *Zero = llvm::Constant::getNullValue(OpTy);
+  Address ResultPtr = CGF.EmitPointerWithAlignment(ResultArg);
+  llvm::Type *ResTy = ResultPtr.getElementType();
+
+  // Take the absolute value of the signed operand.
+  llvm::Value *IsNegative = CGF.Builder.CreateICmpSLT(Signed, Zero);
+  llvm::Value *AbsOfNegative = CGF.Builder.CreateSub(Zero, Signed);
+  llvm::Value *AbsSigned =
+      CGF.Builder.CreateSelect(IsNegative, AbsOfNegative, Signed);
+
+  // Perform a checked unsigned multiplication.
+  llvm::Value *UnsignedOverflow;
+  llvm::Value *UnsignedResult =
+      EmitOverflowIntrinsic(CGF, llvm::Intrinsic::umul_with_overflow, AbsSigned,
+                            Unsigned, UnsignedOverflow);
+
+  llvm::Value *Overflow, *Result;
+  if (ResultInfo.Signed) {
+    // Signed overflow occurs if the result is greater than INT_MAX or lesser
+    // than INT_MIN, i.e when |Result| > (INT_MAX + IsNegative).
+    auto IntMax = llvm::APInt::getSignedMaxValue(ResultInfo.Width)
+                      .zextOrSelf(Op1Info.Width);
+    llvm::Value *MaxResult =
+        CGF.Builder.CreateAdd(llvm::ConstantInt::get(OpTy, IntMax),
+                              CGF.Builder.CreateZExt(IsNegative, OpTy));
+    llvm::Value *SignedOverflow =
+        CGF.Builder.CreateICmpUGT(UnsignedResult, MaxResult);
+    Overflow = CGF.Builder.CreateOr(UnsignedOverflow, SignedOverflow);
+
+    // Prepare the signed result (possibly by negating it).
+    llvm::Value *NegativeResult = CGF.Builder.CreateNeg(UnsignedResult);
+    llvm::Value *SignedResult =
+        CGF.Builder.CreateSelect(IsNegative, NegativeResult, UnsignedResult);
+    Result = CGF.Builder.CreateTrunc(SignedResult, ResTy);
+  } else {
+    // Unsigned overflow occurs if the result is < 0 or greater than UINT_MAX.
+    llvm::Value *Underflow = CGF.Builder.CreateAnd(
+        IsNegative, CGF.Builder.CreateIsNotNull(UnsignedResult));
+    Overflow = CGF.Builder.CreateOr(UnsignedOverflow, Underflow);
+    if (ResultInfo.Width < Op1Info.Width) {
+      auto IntMax =
+          llvm::APInt::getMaxValue(ResultInfo.Width).zext(Op1Info.Width);
+      llvm::Value *TruncOverflow = CGF.Builder.CreateICmpUGT(
+          UnsignedResult, llvm::ConstantInt::get(OpTy, IntMax));
+      Overflow = CGF.Builder.CreateOr(Overflow, TruncOverflow);
+    }
+
+    Result = CGF.Builder.CreateTrunc(UnsignedResult, ResTy);
+  }
+  assert(Overflow && Result && "Missing overflow or result");
+
+  bool isVolatile =
+      ResultArg->getType()->getPointeeType().isVolatileQualified();
+  CGF.Builder.CreateStore(CGF.EmitToMemory(Result, ResultQTy), ResultPtr,
+                          isVolatile);
+  return RValue::get(Overflow);
+}
+
 RValue CodeGenFunction::EmitBuiltinExpr(const FunctionDecl *FD,
                                         unsigned BuiltinID, const CallExpr *E,
                                         ReturnValueSlot ReturnValue) {
@@ -2323,6 +2410,14 @@ RValue CodeGenFunction::EmitBuiltinExpr(const FunctionDecl *FD,
         getIntegerWidthAndSignedness(CGM.getContext(), RightArg->getType());
     WidthAndSignedness ResultInfo =
         getIntegerWidthAndSignedness(CGM.getContext(), ResultQTy);
+
+    // Handle mixed-sign multiplication as a special case, because adding
+    // runtime or backend support for our generic irgen would be too expensive.
+    if (isSpecialMixedSignMultiply(BuiltinID, LeftInfo, RightInfo, ResultInfo))
+      return EmitCheckedMixedSignMultiply(*this, LeftArg, LeftInfo, RightArg,
+                                          RightInfo, ResultArg, ResultQTy,
+                                          ResultInfo);
+
     WidthAndSignedness EncompassingInfo =
         EncompassingIntegerType({LeftInfo, RightInfo, ResultInfo});