The LinkAllPasses.h file is included in several main programs, to force
a large number of passes to be linked in. However, the ForcePassLinking
constructor uses undefined behavior, since it calls member functions on
`nullptr`, e.g.:
((llvm::Function*)nullptr)->viewCFGOnly();
llvm::RGPassManager RGM;
((llvm::RegionPass*)nullptr)->runOnRegion((llvm::Region*)nullptr, RGM);
When the optimization level is -O2 or higher, the code below the first
nullptr dereference is optimized away, and replaced by `ud2` (on x86).
Therefore, the calls after that first dereference are never emitted. In
my case, I noticed there was no call to `llvm::sys::RunningOnValgrind()`!
Replace instances of dereferencing `nullptr` with either objects on the
stack, or regular function calls.
Differential Revision: http://reviews.llvm.org/D15996
llvm-svn: 257645