bindings/go: reinstate TargetMachine.TargetData

[axw]

Summary

LLVMGetTargetDataLayout was removed from the C API,
and then TargetMachine.TargetData was removed. Later,
LLVMCreateTargetMachineData was added to the C API,
and we now expose this via the Go API.

[pcc]

Maybe this should be renamed CreateTargetData to emphasize that the TargetData is owned by the caller. We probably need to update the code in llgo for the new ownership as well.

[deadalnix]

I really don't know much about go. If @pcc don't have the bandwidth to review, I'll dig into this, but I'd prefer to defers to someone more experienced.

[axw]

Rename TargetMachine.TargetData to TargetMachine.CreateTargetData

[axw]

In D18173#375236, @pcc wrote:

Maybe this should be renamed CreateTargetData to emphasize that the TargetData is owned by the caller. We probably need to update the code in llgo for the new ownership as well.

Done. Updated D15188 with the corresponding changes.

[pcc]

LGTM

bindings/go/llvm/target.go

func (t Target) CreateTargetMachine(Triple string, CPU string, Features string,
   defer C.free(unsafe.Pointer(cFeatures))
   tm.C = C.LLVMCreateTargetMachine(t.C, cTriple, cCPU, cFeatures,
     C.LLVMCodeGenOptLevel(Level),
     C.LLVMRelocMode(Reloc),
     C.LLVMCodeModel(CodeModel))
   return
 }
 
+// CreateTargetData returns a new TargetData describing the TargetMachine's
+// data layout. The returned TargetData is owned by the caller, who is
+// responsible for disposing of it by calling the TargetData.Dispose method.
+func (tm TargetMachine) CreateTargetData() TargetData {
+  return TargetData{C.LLVMCreateTargetDataLayout(tm.C)}
+}
+
 // Triple returns the triple describing the machine (arch-vendor-os).
 func (tm TargetMachine) Triple() string {
   cstr := C.LLVMGetTargetMachineTriple(tm.C)
   return C.GoString(cstr)
 }
 
 func (tm TargetMachine) EmitToMemoryBuffer(m Module, ft CodeGenFileType) (MemoryBuffer, error) {
   var errstr *C.char