[NVPTX][AsmPrinter] Avoid removing globals before calling AsmPrinter::doFinalization()

[krisb]

Summary

Instead of removing globals from a module, we, it seems, can just override
AsmPrinter::emitGlobalVariable() to do nothing as NVPTXAsmPrinter already
emitted globals by this time and we don't want to do it twice.

This patch doesn't affect any existing regression tests,
so I'd want to consider it at least as NFCI.

[asavonic]

llvm/lib/Target/NVPTX/NVPTXAsmPrinter.h

310

Can we keep the original comment to explain the problem? Something like:

Do not allow base AsmPrinter doing something with globals: global variables are emitted at the beginning and base AsmPrinter will attempt to do that again in doFinalization().

[tra]

LGTM in general.

llvm/lib/Target/NVPTX/NVPTXAsmPrinter.h

310

+1. We do need a good explanation why we're doing something as odd as not emitting globals.

[krisb]

Make the comment for emitGlobalVariable() more detailed.

[krisb]

Ping

llvm/lib/Target/NVPTX/NVPTXAsmPrinter.h

public:
   void getAnalysisUsage(AnalysisUsage &AU) const override {
     AU.addRequired<MachineLoopInfo>();
     AsmPrinter::getAnalysisUsage(AU);
   }
 
   std::string getVirtualRegisterName(unsigned) const;
 
   const MCSymbol *getFunctionFrameSymbol() const override;
+
+  // Make emitGlobalVariable() no-op for NVPTX.
+  // Global variables have been already emitted by the time the base AsmPrinter
+  // attempts to do so in doFinalization() (see NVPTXAsmPrinter::emitGlobals()).
+  void emitGlobalVariable(const GlobalVariable *GV) override {}
 };
 
 } // end namespace llvm
 
 #endif // LLVM_LIB_TARGET_NVPTX_NVPTXASMPRINTER_H

llvm/lib/Target/NVPTX/NVPTXAsmPrinter.cpp

bool NVPTXAsmPrinter::doFinalization(Module &M) {
 
   // If we did not emit any functions, then the global declarations have not
   // yet been emitted.
   if (!GlobalsEmitted) {
     emitGlobals(M);
     GlobalsEmitted = true;
   }
 
-  // XXX Temproarily remove global variables so that doFinalization() will not
-  // emit them again (global variables are emitted at beginning).
-
-  Module::GlobalListType &global_list = M.getGlobalList();
-  int i, n = global_list.size();
-  GlobalVariable **gv_array = new GlobalVariable *[n];
-
-  // first, back-up GlobalVariable in gv_array
-  i = 0;
-  for (Module::global_iterator I = global_list.begin(), E = global_list.end();
-       I != E; ++I)
-    gv_array[i++] = &*I;
-
-  // second, empty global_list
-  while (!global_list.empty())
-    global_list.remove(global_list.begin());
-
   // call doFinalization
   bool ret = AsmPrinter::doFinalization(M);
 
-  // now we restore global variables
-  for (i = 0; i < n; i++)
-    global_list.insert(global_list.end(), gv_array[i]);
-
   clearAnnotationCache(&M);
 
-  delete[] gv_array;
   // Close the last emitted section
   if (HasDebugInfo) {
     static_cast<NVPTXTargetStreamer *>(OutStreamer->getTargetStreamer())
         ->closeLastSection();
     // Emit empty .debug_loc section for better support of the empty files.
     OutStreamer->emitRawText("\t.section\t.debug_loc\t{\t}");
   }