No -fsanitize=function warning when calling noexcept function through non-noexcept pointer in C++17

As discussed in the mail thread <https://groups.google.com/a/isocpp.org/forum/
#!topic/std-discussion/T64_dW3WKUk> "Calling noexcept function throug non-
noexcept pointer is undefined behavior?", such a call should not be UB.
However, Clang currently warns about it.

This change removes exception specifications from the function types recorded
for -fsanitize=function, both in the functions themselves and at the call sites.
That means that calling a non-noexcept function through a noexcept pointer will
also not be flagged as UB.  In the review of this change, that was deemed
acceptable, at least for now.  (See the "TODO" in compiler-rt
test/ubsan/TestCases/TypeCheck/Function/function.cpp.)

To remove exception specifications from types, the existing internal
ASTContext::getFunctionTypeWithExceptionSpec was made public, and some places
otherwise unrelated to this change have been adapted to call it, too.

This is the cfe part of a patch covering both cfe and compiler-rt.

Differential Revision: https://reviews.llvm.org/D40720


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@321859 91177308-0d34-0410-b5e6-96231b3b80d8

include/clang/AST/ASTContext.h

@@ -1162,6 +1162,13 @@ public:
   /// \brief Change the result type of a function type once it is deduced.
   void adjustDeducedFunctionResultType(FunctionDecl *FD, QualType ResultType);
 
+  /// Get a function type and produce the equivalent function type with the
+  /// specified exception specification. Type sugar that can be present on a
+  /// declaration of a function with an exception specification is permitted
+  /// and preserved. Other type sugar (for instance, typedefs) is not.
+  QualType getFunctionTypeWithExceptionSpec(
+      QualType Orig, const FunctionProtoType::ExceptionSpecInfo &ESI);
+
   /// \brief Determine whether two function types are the same, ignoring
   /// exception specifications in cases where they're part of the type.
   bool hasSameFunctionTypeIgnoringExceptionSpec(QualType T, QualType U);

lib/AST/ASTContext.cpp

@@ -2582,26 +2582,24 @@ void ASTContext::adjustDeducedFunctionResultType(FunctionDecl *FD,
 /// specified exception specification. Type sugar that can be present on a
 /// declaration of a function with an exception specification is permitted
 /// and preserved. Other type sugar (for instance, typedefs) is not.
-static QualType getFunctionTypeWithExceptionSpec(
-    ASTContext &Context, QualType Orig,
-    const FunctionProtoType::ExceptionSpecInfo &ESI) {
+QualType ASTContext::getFunctionTypeWithExceptionSpec(
+    QualType Orig, const FunctionProtoType::ExceptionSpecInfo &ESI) {
   // Might have some parens.
   if (auto *PT = dyn_cast<ParenType>(Orig))
-    return Context.getParenType(
-        getFunctionTypeWithExceptionSpec(Context, PT->getInnerType(), ESI));
+    return getParenType(
+        getFunctionTypeWithExceptionSpec(PT->getInnerType(), ESI));
 
   // Might have a calling-convention attribute.
   if (auto *AT = dyn_cast<AttributedType>(Orig))
-    return Context.getAttributedType(
+    return getAttributedType(
         AT->getAttrKind(),
-        getFunctionTypeWithExceptionSpec(Context, AT->getModifiedType(), ESI),
-        getFunctionTypeWithExceptionSpec(Context, AT->getEquivalentType(),
-                                         ESI));
+        getFunctionTypeWithExceptionSpec(AT->getModifiedType(), ESI),
+        getFunctionTypeWithExceptionSpec(AT->getEquivalentType(), ESI));
 
   // Anything else must be a function type. Rebuild it with the new exception
   // specification.
   const FunctionProtoType *Proto = cast<FunctionProtoType>(Orig);
-  return Context.getFunctionType(
+  return getFunctionType(
       Proto->getReturnType(), Proto->getParamTypes(),
       Proto->getExtProtoInfo().withExceptionSpec(ESI));
 }
@@ -2610,8 +2608,8 @@ bool ASTContext::hasSameFunctionTypeIgnoringExceptionSpec(QualType T,
                                                           QualType U) {
   return hasSameType(T, U) ||
          (getLangOpts().CPlusPlus17 &&
-          hasSameType(getFunctionTypeWithExceptionSpec(*this, T, EST_None),
-                      getFunctionTypeWithExceptionSpec(*this, U, EST_None)));
+          hasSameType(getFunctionTypeWithExceptionSpec(T, EST_None),
+                      getFunctionTypeWithExceptionSpec(U, EST_None)));
 }
 
 void ASTContext::adjustExceptionSpec(
@@ -2619,7 +2617,7 @@ void ASTContext::adjustExceptionSpec(
     bool AsWritten) {
   // Update the type.
   QualType Updated =
-      getFunctionTypeWithExceptionSpec(*this, FD->getType(), ESI);
+      getFunctionTypeWithExceptionSpec(FD->getType(), ESI);
   FD->setType(Updated);
 
   if (!AsWritten)
@@ -2630,7 +2628,7 @@ void ASTContext::adjustExceptionSpec(
     // If the type and the type-as-written differ, we may need to update
     // the type-as-written too.
     if (TSInfo->getType() != FD->getType())
-      Updated = getFunctionTypeWithExceptionSpec(*this, TSInfo->getType(), ESI);
+      Updated = getFunctionTypeWithExceptionSpec(TSInfo->getType(), ESI);
 
     // FIXME: When we get proper type location information for exceptions,
     // we'll also have to rebuild the TypeSourceInfo. For now, we just patch

lib/CodeGen/CGExpr.cpp

@@ -4479,8 +4479,7 @@ RValue CodeGenFunction::EmitCall(QualType CalleeType, const CGCallee &OrigCallee
 
   CalleeType = getContext().getCanonicalType(CalleeType);
 
-  const auto *FnType =
-      cast<FunctionType>(cast<PointerType>(CalleeType)->getPointeeType());
+  auto PointeeType = cast<PointerType>(CalleeType)->getPointeeType();
 
   CGCallee Callee = OrigCallee;
 
@@ -4489,8 +4488,12 @@ RValue CodeGenFunction::EmitCall(QualType CalleeType, const CGCallee &OrigCallee
     if (llvm::Constant *PrefixSig =
             CGM.getTargetCodeGenInfo().getUBSanFunctionSignature(CGM)) {
       SanitizerScope SanScope(this);
+      // Remove any (C++17) exception specifications, to allow calling e.g. a
+      // noexcept function through a non-noexcept pointer.
+      auto ProtoTy =
+        getContext().getFunctionTypeWithExceptionSpec(PointeeType, EST_None);
       llvm::Constant *FTRTTIConst =
-          CGM.GetAddrOfRTTIDescriptor(QualType(FnType, 0), /*ForEH=*/true);
+          CGM.GetAddrOfRTTIDescriptor(ProtoTy, /*ForEH=*/true);
       llvm::Type *PrefixStructTyElems[] = {PrefixSig->getType(), Int32Ty};
       llvm::StructType *PrefixStructTy = llvm::StructType::get(
           CGM.getLLVMContext(), PrefixStructTyElems, /*isPacked=*/true);
@@ -4530,6 +4533,8 @@ RValue CodeGenFunction::EmitCall(QualType CalleeType, const CGCallee &OrigCallee
     }
   }
 
+  const auto *FnType = cast<FunctionType>(PointeeType);
+
   // If we are checking indirect calls and this call is indirect, check that the
   // function pointer is a member of the bit set for the function type.
   if (SanOpts.has(SanitizerKind::CFIICall) &&

lib/CodeGen/CodeGenFunction.cpp

@@ -924,8 +924,13 @@ void CodeGenFunction::StartFunction(GlobalDecl GD,
   if (getLangOpts().CPlusPlus && SanOpts.has(SanitizerKind::Function)) {
     if (const FunctionDecl *FD = dyn_cast_or_null<FunctionDecl>(D)) {
       if (llvm::Constant *PrologueSig = getPrologueSignature(CGM, FD)) {
+        // Remove any (C++17) exception specifications, to allow calling e.g. a
+        // noexcept function through a non-noexcept pointer.
+        auto ProtoTy =
+          getContext().getFunctionTypeWithExceptionSpec(FD->getType(),
+                                                        EST_None);
         llvm::Constant *FTRTTIConst =
-            CGM.GetAddrOfRTTIDescriptor(FD->getType(), /*ForEH=*/true);
+            CGM.GetAddrOfRTTIDescriptor(ProtoTy, /*ForEH=*/true);
         llvm::Constant *FTRTTIConstEncoded =
             EncodeAddrForUseInPrologue(Fn, FTRTTIConst);
         llvm::Constant *PrologueStructElems[] = {PrologueSig,

lib/CodeGen/ItaniumCXXABI.cpp

@@ -3435,9 +3435,7 @@ static unsigned extractPBaseFlags(ASTContext &Ctx, QualType &Type) {
   if (auto *Proto = Type->getAs<FunctionProtoType>()) {
     if (Proto->isNothrow(Ctx)) {
       Flags |= ItaniumRTTIBuilder::PTI_Noexcept;
-      Type = Ctx.getFunctionType(
-          Proto->getReturnType(), Proto->getParamTypes(),
-          Proto->getExtProtoInfo().withExceptionSpec(EST_None));
+      Type = Ctx.getFunctionTypeWithExceptionSpec(Type, EST_None);
     }
   }
 

lib/Sema/SemaOverload.cpp

@@ -1475,10 +1475,8 @@ bool Sema::IsFunctionConversion(QualType FromType, QualType ToType,
     const auto *ToFPT = cast<FunctionProtoType>(ToFn);
     if (FromFPT->isNothrow(Context) && !ToFPT->isNothrow(Context)) {
       FromFn = cast<FunctionType>(
-          Context.getFunctionType(FromFPT->getReturnType(),
-                                  FromFPT->getParamTypes(),
-                                  FromFPT->getExtProtoInfo().withExceptionSpec(
-                                      FunctionProtoType::ExceptionSpecInfo()))
+          Context.getFunctionTypeWithExceptionSpec(QualType(FromFPT, 0),
+                                                   EST_None)
                  .getTypePtr());
       Changed = true;
     }