Add a TargetMachine hook that verifies DataLayout compatibility

[mehdi_amini]

Summary

Also provide the associated assertion when CodeGen starts.

[echristo]

This assert will only be valid as long as we create (or can create) a data layout in the backend right?

-eric

include/llvm/Target/TargetMachine.h

138–141

"is used for optimizations and code generation"?
"This hook provides a..."
"The default implementation just checks..." though do we really need a target override here?

[mehdi_amini]

include/llvm/Target/TargetMachine.h

138–141

I was not sure for the Target override, can we imagine that a Target is more flexible on the DataLayout requirement? Can it accept variation on some aspects?
If it does not make sense I'll make it non virtual.

[echristo]

include/llvm/Target/TargetMachine.h

138–141

Yeah, it makes sense eventually. Maybe not at the moment? Entirely up to you though. :)

[mehdi_amini]

Remove the virtual keyword, we can bring it back when we'll have a use-case

[echristo]

Sorry, meant to accept this earlier. Thanks :)

-eric

[mehdi_amini]

landed

include/llvm/Target/TargetMachine.h

public:
   /// returned is of the correct type.
   template <typename STC> const STC &getSubtarget(const Function &F) const {
     return *static_cast<const STC*>(getSubtargetImpl(F));
   }
 
   /// Create a DataLayout.
   const DataLayout createDataLayout() const { return DL; }
 
+  /// Test if a DataLayout if compatible with the CodeGen for this target.
+  ///
+  /// The LLVM Module owns a DataLayout that is used for the target independent
+  /// optimizations and code generation. This hook provides a target specific
+  /// check on the validity of this DataLayout.
+  bool isCompatibleDataLayout(const DataLayout &Candidate) const {
+    return DL == Candidate;
+  }
+
   /// Get the pointer size for this target.
   ///
   /// This is the only time the DataLayout in the TargetMachine is used.
   unsigned getPointerSize() const { return DL.getPointerSize(); }
 
   /// \brief Reset the target options based on the function's attributes.
   // FIXME: Remove TargetOptions that affect per-function code generation
   // from TargetMachine.

lib/CodeGen/MachineFunction.cpp

MachineFunction::MachineFunction(const Function *F, const TargetMachine &TM,
 
   // FIXME: Shouldn't use pref alignment if explicit alignment is set on Fn.
   if (!Fn->hasFnAttribute(Attribute::OptimizeForSize))
     Alignment = std::max(Alignment,
                          STI->getTargetLowering()->getPrefFunctionAlignment());
 
   FunctionNumber = FunctionNum;
   JumpTableInfo = nullptr;
+
+  assert(TM.isCompatibleDataLayout(getDataLayout()) &&
+         "Can't create a MachineFunction using a Module with a "
+         "Target-incompatible DataLayout attached\n");
 }
 
 MachineFunction::~MachineFunction() {
   // Don't call destructors on MachineInstr and MachineOperand. All of their
   // memory comes from the BumpPtrAllocator which is about to be purged.
   //
   // Do call MachineBasicBlock destructors, it contains std::vectors.
   for (iterator I = begin(), E = end(); I != E; I = BasicBlocks.erase(I))