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

llvm-svn: 321859

1 files changed, 6 insertions, 1 deletions

diff --git a/clang/lib/CodeGen/CodeGenFunction.cpp b/clang/lib/CodeGen/CodeGenFunction.cpp
index 664b5107842..6fb21b15736 100644
--- a/clang/lib/CodeGen/CodeGenFunction.cpp
+++ b/clang/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,