Protect against filenames with no extension at all.

[saugustine]

Summary

Such as the one in the darwin-dsymutil.c test.

[JDevlieghere]

Can you add a test that exercises this code path?

[saugustine]

The darwin-dsymutil.c tests this code path right now on line 33. I found this error by running it under asan; otherwise it was fully latent.

It seems pretty clear to me that when End == -1 (StringRef::npos), creating a string ref from that is obviously a bug.

I'm not even sure how to check for a failure. clang will almost never crash; there is just a very subtle bounds violation or empty stringref. How it manifests itself depends on subsequent usage of the stringref, and stack layout.

[echristo]

Could maybe add an assert along with the patch as well as an assert only
test?

clang/lib/Driver/Driver.cpp

if ((JA.getType() == types::TY_Object || JA.getType() == types::TY_LTO_BC) &&
     NamedOutput = C.getArgs().MakeArgString(GetClPchPath(C, BaseName));
   } else {
     const char *Suffix = types::getTypeTempSuffix(JA.getType(), IsCLMode());
     assert(Suffix && "All types used for output should have a suffix.");
 
     std::string::size_type End = std::string::npos;
     if (!types::appendSuffixForType(JA.getType()))
       End = BaseName.rfind('.');
+    if (End == StringRef::npos)
+      End = BaseName.size();
     SmallString<128> Suffixed(BaseName.substr(0, End));
     Suffixed += OffloadingPrefix;
     if (MultipleArchs && !BoundArch.empty()) {
       Suffixed += "-";
       Suffixed.append(BoundArch);
     }
     // When using both -save-temps and -emit-llvm, use a ".tmp.bc" suffix for
     // the unoptimized bitcode so that it does not get overwritten by the ".bc"