1 //===-- GlobalMerge.cpp - Internal globals merging  -----------------------===//
9 // This pass merges globals with internal linkage into one. This way all the
10 // globals which were merged into a biggest one can be addressed using offsets
13 // when many globals are involved.
53 // However, merging globals can have tradeoffs:
105     cl::desc("Improve global merge pass to ignore globals only used alone"),
119 STATISTIC(NumMerged, "Number of globals merged");
130     /// Currently, this applies a dead simple heuristic: only consider globals
140     bool doMerge(SmallVectorImpl<GlobalVariable*> &Globals,
142     /// \brief Merge everything in \p Globals for which the corresponding bit
144     bool doMerge(const SmallVectorImpl<GlobalVariable *> &Globals,
186       return "Merge internal globals";  in getPassName()
202 bool GlobalMerge::doMerge(SmallVectorImpl<GlobalVariable*> &Globals,  in doMerge()  argument
206   std::stable_sort(Globals.begin(), Globals.end(),  in doMerge()
212   // If we want to just blindly group all globals together, do so.  in doMerge()
214     BitVector AllGlobals(Globals.size());  in doMerge()
216     return doMerge(Globals, AllGlobals, M, isConst, AddrSpace);  in doMerge()
220   // discover all sets of globals used together, and how many times each of  in doMerge()
225   // code (currently, a Function) to the set of globals seen so far that are  in doMerge()
231   //   combination of the previous N-1 globals.  in doMerge()
237   // We keep track of the sets of globals used together "close enough".  in doMerge()
239     UsedGlobalSet(size_t Size) : Globals(Size), UsageCount(1) {}  in doMerge()
240     BitVector Globals;  in doMerge()  member
249     UsedGlobalSets.emplace_back(Globals.size());  in doMerge()
277   for (size_t GI = 0, GE = Globals.size(); GI != GE; ++GI) {  in doMerge()
278     GlobalVariable *GV = Globals[GI];  in doMerge()
327             CreateGlobalSet().Globals.set(GI);  in doMerge()
337         if (UsedGlobalSets[UGSIdx].Globals.test(GI)) {  in doMerge()
359         NewUGS.Globals.set(GI);  in doMerge()
360         NewUGS.Globals |= UsedGlobalSets[UGSIdx].Globals;  in doMerge()
365   // Now we found a bunch of sets of globals used together.  We accumulated  in doMerge()
367   // that use that exact set of globals).  in doMerge()
373               return UGS1.Globals.count() * UGS1.UsageCount <  in doMerge()
374                      UGS2.Globals.count() * UGS2.UsageCount;  in doMerge()
377   // We can choose to merge all globals together, but ignore globals never used  in doMerge()
381     BitVector AllGlobals(Globals.size());  in doMerge()
386       if (UGS.Globals.count() > 1)  in doMerge()
387         AllGlobals |= UGS.Globals;  in doMerge()
389     return doMerge(Globals, AllGlobals, M, isConst, AddrSpace);  in doMerge()
398   BitVector PickedGlobals(Globals.size());  in doMerge()
405     if (PickedGlobals.anyCommon(UGS.Globals))  in doMerge()
407     PickedGlobals |= UGS.Globals;  in doMerge()
411     if (UGS.Globals.count() < 2)  in doMerge()
413     Changed |= doMerge(Globals, UGS.Globals, M, isConst, AddrSpace);  in doMerge()
419 bool GlobalMerge::doMerge(const SmallVectorImpl<GlobalVariable *> &Globals,  in doMerge()  argument
422   assert(Globals.size() > 1);  in doMerge()
438       Type *Ty = Globals[j]->getValueType();  in doMerge()
444       Inits.push_back(Globals[j]->getInitializer());  in doMerge()
455       GlobalValue::LinkageTypes Linkage = Globals[k]->getLinkage();  in doMerge()
456       std::string Name = Globals[k]->getName();  in doMerge()
464       Globals[k]->replaceAllUsesWith(GEP);  in doMerge()
465       Globals[k]->eraseFromParent();  in doMerge()
510       // Look for globals in the clauses of the landing pad instruction  in setMustKeepGlobalVariables()
528   DenseMap<unsigned, SmallVector<GlobalVariable*, 16> > Globals, ConstGlobals,  in doInitialization()  local
533   // Grab all non-const globals.  in doInitialization()
534   for (auto &GV : M.globals()) {  in doInitialization()
535     // Merge is safe for "normal" internal or external globals only  in doInitialization()
548     // Ignore fancy-aligned globals for now.  in doInitialization()
554     // Ignore all 'special' globals.  in doInitialization()
559     // Ignore all "required" globals:  in doInitialization()
570         Globals[AddressSpace].push_back(&GV);  in doInitialization()
574   for (auto &P : Globals)  in doInitialization()