1 files changed, 71 insertions, 4 deletions

diff --git a/clang/lib/CodeGen/CGExprScalar.cpp b/clang/lib/CodeGen/CGExprScalar.cpp
index 63031d44644..c14e6d12da8 100644
--- a/clang/lib/CodeGen/CGExprScalar.cpp
+++ b/clang/lib/CodeGen/CGExprScalar.cpp
@@ -24,6 +24,7 @@
 #include "clang/AST/StmtVisitor.h"
 #include "clang/Basic/TargetInfo.h"
 #include "clang/Frontend/CodeGenOptions.h"
+#include "llvm/ADT/Optional.h"
 #include "llvm/IR/CFG.h"
 #include "llvm/IR/Constants.h"
 #include "llvm/IR/DataLayout.h"
@@ -58,6 +59,59 @@ static bool MustVisitNullValue(const Expr *E) {
   return E->getType()->isNullPtrType();
 }
 
+/// If \p E is a widened promoted integer, get its base (unpromoted) type.
+static llvm::Optional<QualType> getUnwidenedIntegerType(const ASTContext &Ctx,
+                                                        const Expr *E) {
+  const Expr *Base = E->IgnoreImpCasts();
+  if (E == Base)
+    return llvm::None;
+
+  QualType BaseTy = Base->getType();
+  if (!BaseTy->isPromotableIntegerType() ||
+      Ctx.getTypeSize(BaseTy) >= Ctx.getTypeSize(E->getType()))
+    return llvm::None;
+
+  return BaseTy;
+}
+
+/// Check if \p E is a widened promoted integer.
+static bool IsWidenedIntegerOp(const ASTContext &Ctx, const Expr *E) {
+  return getUnwidenedIntegerType(Ctx, E).hasValue();
+}
+
+/// Check if we can skip the overflow check for \p Op.
+static bool CanElideOverflowCheck(const ASTContext &Ctx, const BinOpInfo &Op) {
+  assert(isa<UnaryOperator>(Op.E) ||
+         isa<BinaryOperator>(Op.E) && "Expected a unary or binary operator");
+
+  if (const auto *UO = dyn_cast<UnaryOperator>(Op.E))
+    return IsWidenedIntegerOp(Ctx, UO->getSubExpr());
+
+  const auto *BO = cast<BinaryOperator>(Op.E);
+  auto OptionalLHSTy = getUnwidenedIntegerType(Ctx, BO->getLHS());
+  if (!OptionalLHSTy)
+    return false;
+
+  auto OptionalRHSTy = getUnwidenedIntegerType(Ctx, BO->getRHS());
+  if (!OptionalRHSTy)
+    return false;
+
+  QualType LHSTy = *OptionalLHSTy;
+  QualType RHSTy = *OptionalRHSTy;
+
+  // We usually don't need overflow checks for binary operations with widened
+  // operands. Multiplication with promoted unsigned operands is a special case.
+  if ((Op.Opcode != BO_Mul && Op.Opcode != BO_MulAssign) ||
+      !LHSTy->isUnsignedIntegerType() || !RHSTy->isUnsignedIntegerType())
+    return true;
+
+  // The overflow check can be skipped if either one of the unpromoted types
+  // are less than half the size of the promoted type.
+  unsigned PromotedSize = Ctx.getTypeSize(Op.E->getType());
+  return (2 * Ctx.getTypeSize(LHSTy)) < PromotedSize ||
+         (2 * Ctx.getTypeSize(RHSTy)) < PromotedSize;
+}
+
 class ScalarExprEmitter
   : public StmtVisitor<ScalarExprEmitter, Value*> {
   CodeGenFunction &CGF;
@@ -482,12 +536,15 @@ public:
           return Builder.CreateNSWMul(Ops.LHS, Ops.RHS, "mul");
         // Fall through.
       case LangOptions::SOB_Trapping:
+        if (CanElideOverflowCheck(CGF.getContext(), Ops))
+          return Builder.CreateNSWMul(Ops.LHS, Ops.RHS, "mul");
         return EmitOverflowCheckedBinOp(Ops);
       }
     }
 
     if (Ops.Ty->isUnsignedIntegerType() &&
-        CGF.SanOpts.has(SanitizerKind::UnsignedIntegerOverflow))
+        CGF.SanOpts.has(SanitizerKind::UnsignedIntegerOverflow) &&
+        !CanElideOverflowCheck(CGF.getContext(), Ops))
       return EmitOverflowCheckedBinOp(Ops);
 
     if (Ops.LHS->getType()->isFPOrFPVectorTy())
@@ -1663,6 +1720,8 @@ llvm::Value *ScalarExprEmitter::EmitIncDecConsiderOverflowBehavior(
       return Builder.CreateNSWAdd(InVal, Amount, Name);
     // Fall through.
   case LangOptions::SOB_Trapping:
+    if (IsWidenedIntegerOp(CGF.getContext(), E->getSubExpr()))
+      return Builder.CreateNSWAdd(InVal, Amount, Name);
     return EmitOverflowCheckedBinOp(createBinOpInfoFromIncDec(E, InVal, IsInc));
   }
   llvm_unreachable("Unknown SignedOverflowBehaviorTy");
@@ -2281,8 +2340,10 @@ void ScalarExprEmitter::EmitUndefinedBehaviorIntegerDivAndRemCheck(
                                     SanitizerKind::IntegerDivideByZero));
   }
 
+  const auto *BO = cast<BinaryOperator>(Ops.E);
   if (CGF.SanOpts.has(SanitizerKind::SignedIntegerOverflow) &&
-      Ops.Ty->hasSignedIntegerRepresentation()) {
+      Ops.Ty->hasSignedIntegerRepresentation() &&
+      !IsWidenedIntegerOp(CGF.getContext(), BO->getLHS())) {
     llvm::IntegerType *Ty = cast<llvm::IntegerType>(Zero->getType());
 
     llvm::Value *IntMin =
@@ -2634,12 +2695,15 @@ Value *ScalarExprEmitter::EmitAdd(const BinOpInfo &op) {
         return Builder.CreateNSWAdd(op.LHS, op.RHS, "add");
       // Fall through.
     case LangOptions::SOB_Trapping:
+      if (CanElideOverflowCheck(CGF.getContext(), op))
+        return Builder.CreateNSWAdd(op.LHS, op.RHS, "add");
       return EmitOverflowCheckedBinOp(op);
     }
   }
 
   if (op.Ty->isUnsignedIntegerType() &&
-      CGF.SanOpts.has(SanitizerKind::UnsignedIntegerOverflow))
+      CGF.SanOpts.has(SanitizerKind::UnsignedIntegerOverflow) &&
+      !CanElideOverflowCheck(CGF.getContext(), op))
     return EmitOverflowCheckedBinOp(op);
 
   if (op.LHS->getType()->isFPOrFPVectorTy()) {
@@ -2665,12 +2729,15 @@ Value *ScalarExprEmitter::EmitSub(const BinOpInfo &op) {
           return Builder.CreateNSWSub(op.LHS, op.RHS, "sub");
         // Fall through.
       case LangOptions::SOB_Trapping:
+        if (CanElideOverflowCheck(CGF.getContext(), op))
+          return Builder.CreateNSWSub(op.LHS, op.RHS, "sub");
         return EmitOverflowCheckedBinOp(op);
       }
     }
 
     if (op.Ty->isUnsignedIntegerType() &&
-        CGF.SanOpts.has(SanitizerKind::UnsignedIntegerOverflow))
+        CGF.SanOpts.has(SanitizerKind::UnsignedIntegerOverflow) &&
+        !CanElideOverflowCheck(CGF.getContext(), op))
       return EmitOverflowCheckedBinOp(op);
 
     if (op.LHS->getType()->isFPOrFPVectorTy()) {