[llvm][clang][mlir] Add checks for the return values from Target::createXXX to prevent protential null deref

All these potential null pointer dereferences are reported by my static analyzer for null smart pointer dereferences, which has a different implementation from `alpha.cplusplus.SmartPtr`.

The checked pointers in this patch are initialized by Target::createXXX functions. When the creator function pointer is not correctly set, a null pointer will be returned, or the creator function may originally return a null pointer.

Some of them may not make sense as they may be checked before entering the function, but I fixed them all in this patch. I submit this fix because 1) similar checks are found in some other places in the LLVM codebase for the same return value of the function; and, 2) some of the pointers are dereferenced before they are checked, which may definitely trigger a null pointer dereference if the return value is nullptr.

Reviewed By: tejohnson, MaskRay, jpienaar

Differential Revision: https://reviews.llvm.org/D91410

1 files changed, 3 insertions, 1 deletions

diff --git a/llvm/lib/LTO/LTOBackend.cpp b/llvm/lib/LTO/LTOBackend.cpp
index 635584a..3365880 100644
--- a/llvm/lib/LTO/LTOBackend.cpp
+++ b/llvm/lib/LTO/LTOBackend.cpp
@@ -199,9 +199,11 @@ createTargetMachine(const Config &Conf, const Target *TheTarget, Module &M) {
   else
     CodeModel = M.getCodeModel();
 
-  return std::unique_ptr<TargetMachine>(TheTarget->createTargetMachine(
+  std::unique_ptr<TargetMachine> TM(TheTarget->createTargetMachine(
       TheTriple, Conf.CPU, Features.getString(), Conf.Options, RelocModel,
       CodeModel, Conf.CGOptLevel));
+  assert(TM && "Failed to create target machine");
+  return TM;
 }
 
 static void runNewPMPasses(const Config &Conf, Module &Mod, TargetMachine *TM,