PR44514: Fix recovery from noexcept with non-convertible expressions

[erichkeane]

Summary

We currently treat noexcept(not-convertible-to-bool) as 'none', which
results in the typeloc info being a different size, and causing an
assert later on in the process. In order to make recovery less
destructive, replace this with noexcept(false) and a constructed 'false'
expression.

[aaron.ballman]

LGTM aside from a simplification. Can you mention the LLVM bug report in the commit log, as well (and close the bug)?

clang/lib/Sema/SemaExceptionSpec.cpp

90–92

This can be simplified with APSInt::getUnsigned() unless you reallllly need it to be a one-bit integer.

[erichkeane]

clang/lib/Sema/SemaExceptionSpec.cpp

90–92

We normally DO create it as a 1 bit APSInt (the return type of the ConstantExpr), as discussed on IRC we should probably not differ from that.

clang/lib/Sema/SemaExceptionSpec.cpp

return llvm::StringSwitch<bool>(RD->getIdentifier()->getName())
       .Default(false);
 }
 
 ExprResult Sema::ActOnNoexceptSpec(SourceLocation NoexceptLoc,
                                    Expr *NoexceptExpr,
                                    ExceptionSpecificationType &EST) {
   // FIXME: This is bogus, a noexcept expression is not a condition.
   ExprResult Converted = CheckBooleanCondition(NoexceptLoc, NoexceptExpr);
-  if (Converted.isInvalid())
-    return Converted;
+  if (Converted.isInvalid()) {
+    EST = EST_NoexceptFalse;
+
+    // Fill in an expression of 'false' as a fixup.
+    auto *BoolExpr = new (Context)
+        CXXBoolLiteralExpr(false, Context.BoolTy, NoexceptExpr->getBeginLoc());
+    llvm::APSInt Value{1};
+    Value = 0;
+    return ConstantExpr::Create(Context, BoolExpr, APValue{Value});
+  }
 
   if (Converted.get()->isValueDependent()) {
     EST = EST_DependentNoexcept;
     return Converted;
   }
 
   llvm::APSInt Result;
   Converted = VerifyIntegerConstantExpression(

clang/test/SemaCXX/cxx0x-noexcept-expression.cpp

void vla(bool b) {
   // FIXME: This can't actually throw, but we conservatively assume any VLA
   // type can throw for now.
   static_assert(!noexcept(static_cast<int(*)[b ? 41 : 42]>(0)), "");
   static_assert(!noexcept(static_cast<int(*)[b ? throw : 42]>(0)), "");
   static_assert(!noexcept(reinterpret_cast<int(*)[b ? throw : 42]>(0)), "");
   static_assert(!noexcept((int(*)[b ? throw : 42])0), "");
   static_assert(!noexcept((int(*)[b ? throw : 42]){0}), "");
 }
+
+struct pr_44514 {
+  // expected-error@+1{{value of type 'void' is not contextually convertible to 'bool'}}
+  void foo(void) const &noexcept(f());
+};