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Devang Patel76c85632011-10-17 17:17:43 +00001//===-- GlobalMerge.cpp - Internal globals merging -----------------------===//
Anton Korobeynikov19edda02010-07-24 21:52:08 +00002//
3// The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
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
11// from the same base pointer (no need for separate base pointer for each of the
12// global). Such a transformation can significantly reduce the register pressure
13// when many globals are involved.
14//
Nadav Rotem465834c2012-07-24 10:51:42 +000015// For example, consider the code which touches several global variables at
Eric Christopherbf86fd32010-09-28 04:18:29 +000016// once:
Anton Korobeynikov19edda02010-07-24 21:52:08 +000017//
18// static int foo[N], bar[N], baz[N];
19//
20// for (i = 0; i < N; ++i) {
21// foo[i] = bar[i] * baz[i];
22// }
23//
24// On ARM the addresses of 3 arrays should be kept in the registers, thus
25// this code has quite large register pressure (loop body):
26//
27// ldr r1, [r5], #4
28// ldr r2, [r6], #4
29// mul r1, r2, r1
30// str r1, [r0], #4
31//
32// Pass converts the code to something like:
33//
34// static struct {
35// int foo[N];
36// int bar[N];
37// int baz[N];
38// } merged;
39//
40// for (i = 0; i < N; ++i) {
41// merged.foo[i] = merged.bar[i] * merged.baz[i];
42// }
43//
44// and in ARM code this becomes:
45//
46// ldr r0, [r5, #40]
47// ldr r1, [r5, #80]
48// mul r0, r1, r0
49// str r0, [r5], #4
50//
51// note that we saved 2 registers here almostly "for free".
Ahmed Bougacha279e3ee2015-04-18 01:21:58 +000052//
53// However, merging globals can have tradeoffs:
54// - it confuses debuggers, tools, and users
55// - it makes linker optimizations less useful (order files, LOHs, ...)
56// - it forces usage of indexed addressing (which isn't necessarily "free")
57// - it can increase register pressure when the uses are disparate enough.
58//
59// We use heuristics to discover the best global grouping we can (cf cl::opts).
Eric Christopherbf86fd32010-09-28 04:18:29 +000060// ===---------------------------------------------------------------------===//
Anton Korobeynikov19edda02010-07-24 21:52:08 +000061
Ahmed Bougacha279e3ee2015-04-18 01:21:58 +000062#include "llvm/ADT/DenseMap.h"
63#include "llvm/ADT/SmallBitVector.h"
Quentin Colombet8fc34092013-03-18 22:30:07 +000064#include "llvm/ADT/SmallPtrSet.h"
Chandler Carruthed0881b2012-12-03 16:50:05 +000065#include "llvm/ADT/Statistic.h"
Chandler Carruthd9903882015-01-14 11:23:27 +000066#include "llvm/CodeGen/Passes.h"
Chandler Carruth9fb823b2013-01-02 11:36:10 +000067#include "llvm/IR/Attributes.h"
68#include "llvm/IR/Constants.h"
69#include "llvm/IR/DataLayout.h"
70#include "llvm/IR/DerivedTypes.h"
71#include "llvm/IR/Function.h"
72#include "llvm/IR/GlobalVariable.h"
73#include "llvm/IR/Instructions.h"
74#include "llvm/IR/Intrinsics.h"
75#include "llvm/IR/Module.h"
Anton Korobeynikov19edda02010-07-24 21:52:08 +000076#include "llvm/Pass.h"
Quentin Colombet8fc34092013-03-18 22:30:07 +000077#include "llvm/Support/CommandLine.h"
Ahmed Bougacha279e3ee2015-04-18 01:21:58 +000078#include "llvm/Support/Debug.h"
79#include "llvm/Support/raw_ostream.h"
Anton Korobeynikov19edda02010-07-24 21:52:08 +000080#include "llvm/Target/TargetLowering.h"
Bob Wilson881b45c2010-11-17 21:25:39 +000081#include "llvm/Target/TargetLoweringObjectFile.h"
Eric Christopherd9134482014-08-04 21:25:23 +000082#include "llvm/Target/TargetSubtargetInfo.h"
Ahmed Bougacha279e3ee2015-04-18 01:21:58 +000083#include <algorithm>
Anton Korobeynikov19edda02010-07-24 21:52:08 +000084using namespace llvm;
85
Chandler Carruth964daaa2014-04-22 02:55:47 +000086#define DEBUG_TYPE "global-merge"
87
Ahmed Bougachab96444e2015-04-11 00:06:36 +000088// FIXME: This is only useful as a last-resort way to disable the pass.
Quentin Colombet8fc34092013-03-18 22:30:07 +000089static cl::opt<bool>
Jiangning Liu3e5b8552014-06-11 06:35:26 +000090EnableGlobalMerge("enable-global-merge", cl::Hidden,
Ahmed Bougachab96444e2015-04-11 00:06:36 +000091 cl::desc("Enable the global merge pass"),
Tim Northoverf804c172014-02-18 11:17:29 +000092 cl::init(true));
93
Peter Collingbournefe12d0e2016-05-19 04:38:56 +000094static cl::opt<unsigned>
95GlobalMergeMaxOffset("global-merge-max-offset", cl::Hidden,
96 cl::desc("Set maximum offset for global merge pass"),
97 cl::init(0));
98
Ahmed Bougacha279e3ee2015-04-18 01:21:58 +000099static cl::opt<bool> GlobalMergeGroupByUse(
100 "global-merge-group-by-use", cl::Hidden,
101 cl::desc("Improve global merge pass to look at uses"), cl::init(true));
102
103static cl::opt<bool> GlobalMergeIgnoreSingleUse(
104 "global-merge-ignore-single-use", cl::Hidden,
105 cl::desc("Improve global merge pass to ignore globals only used alone"),
106 cl::init(true));
107
Tim Northoverf804c172014-02-18 11:17:29 +0000108static cl::opt<bool>
Quentin Colombet8fc34092013-03-18 22:30:07 +0000109EnableGlobalMergeOnConst("global-merge-on-const", cl::Hidden,
Jakub Staszak6b36db02013-07-22 21:11:30 +0000110 cl::desc("Enable global merge pass on constants"),
111 cl::init(false));
Quentin Colombet8fc34092013-03-18 22:30:07 +0000112
Jiangning Liub2ae37f2014-06-11 06:44:53 +0000113// FIXME: this could be a transitional option, and we probably need to remove
114// it if only we are sure this optimization could always benefit all targets.
John Brawn8b954242015-08-03 12:08:41 +0000115static cl::opt<cl::boolOrDefault>
Jiangning Liub2ae37f2014-06-11 06:44:53 +0000116EnableGlobalMergeOnExternal("global-merge-on-external", cl::Hidden,
John Brawn8b954242015-08-03 12:08:41 +0000117 cl::desc("Enable global merge pass on external linkage"));
Jiangning Liub2ae37f2014-06-11 06:44:53 +0000118
Eric Christophered47b222015-02-23 19:28:45 +0000119STATISTIC(NumMerged, "Number of globals merged");
Anton Korobeynikov19edda02010-07-24 21:52:08 +0000120namespace {
Devang Patel76c85632011-10-17 17:17:43 +0000121 class GlobalMerge : public FunctionPass {
Bill Wendling7a639ea2013-06-19 21:07:11 +0000122 const TargetMachine *TM;
Eric Christophered47b222015-02-23 19:28:45 +0000123 // FIXME: Infer the maximum possible offset depending on the actual users
124 // (these max offsets are different for the users inside Thumb or ARM
125 // functions), see the code that passes in the offset in the ARM backend
126 // for more information.
127 unsigned MaxOffset;
Anton Korobeynikov19edda02010-07-24 21:52:08 +0000128
Ahmed Bougacha82076412015-06-04 20:39:23 +0000129 /// Whether we should try to optimize for size only.
130 /// Currently, this applies a dead simple heuristic: only consider globals
131 /// used in minsize functions for merging.
132 /// FIXME: This could learn about optsize, and be used in the cost model.
133 bool OnlyOptimizeForSize;
134
John Brawn8b954242015-08-03 12:08:41 +0000135 /// Whether we should merge global variables that have external linkage.
136 bool MergeExternalGlobals;
137
Peter Collingbournefe12d0e2016-05-19 04:38:56 +0000138 bool IsMachO;
139
Anton Korobeynikov19edda02010-07-24 21:52:08 +0000140 bool doMerge(SmallVectorImpl<GlobalVariable*> &Globals,
Silviu Barangaa055aab2013-01-07 12:31:25 +0000141 Module &M, bool isConst, unsigned AddrSpace) const;
Ahmed Bougacha279e3ee2015-04-18 01:21:58 +0000142 /// \brief Merge everything in \p Globals for which the corresponding bit
143 /// in \p GlobalSet is set.
David Blaikie47bf5c02015-08-21 22:19:06 +0000144 bool doMerge(const SmallVectorImpl<GlobalVariable *> &Globals,
Ahmed Bougacha279e3ee2015-04-18 01:21:58 +0000145 const BitVector &GlobalSet, Module &M, bool isConst,
146 unsigned AddrSpace) const;
Anton Korobeynikov19edda02010-07-24 21:52:08 +0000147
Quentin Colombet8fc34092013-03-18 22:30:07 +0000148 /// \brief Check if the given variable has been identified as must keep
149 /// \pre setMustKeepGlobalVariables must have been called on the Module that
150 /// contains GV
151 bool isMustKeepGlobalVariable(const GlobalVariable *GV) const {
152 return MustKeepGlobalVariables.count(GV);
153 }
154
155 /// Collect every variables marked as "used" or used in a landing pad
156 /// instruction for this Module.
157 void setMustKeepGlobalVariables(Module &M);
158
159 /// Collect every variables marked as "used"
160 void collectUsedGlobalVariables(Module &M);
161
Quentin Colombet2393cb92013-03-19 21:46:49 +0000162 /// Keep track of the GlobalVariable that must not be merged away
Quentin Colombet8fc34092013-03-18 22:30:07 +0000163 SmallPtrSet<const GlobalVariable *, 16> MustKeepGlobalVariables;
164
Anton Korobeynikov19edda02010-07-24 21:52:08 +0000165 public:
166 static char ID; // Pass identification, replacement for typeid.
Peter Collingbournefe12d0e2016-05-19 04:38:56 +0000167 explicit GlobalMerge()
168 : FunctionPass(ID), TM(nullptr), MaxOffset(GlobalMergeMaxOffset),
169 OnlyOptimizeForSize(false), MergeExternalGlobals(false) {
170 initializeGlobalMergePass(*PassRegistry::getPassRegistry());
171 }
172
173 explicit GlobalMerge(const TargetMachine *TM, unsigned MaximalOffset,
174 bool OnlyOptimizeForSize, bool MergeExternalGlobals)
Mehdi Aminif6727b02015-07-07 18:49:25 +0000175 : FunctionPass(ID), TM(TM), MaxOffset(MaximalOffset),
John Brawn8b954242015-08-03 12:08:41 +0000176 OnlyOptimizeForSize(OnlyOptimizeForSize),
177 MergeExternalGlobals(MergeExternalGlobals) {
Devang Patel76c85632011-10-17 17:17:43 +0000178 initializeGlobalMergePass(*PassRegistry::getPassRegistry());
179 }
Anton Korobeynikov19edda02010-07-24 21:52:08 +0000180
Craig Topper3e4c6972014-03-05 09:10:37 +0000181 bool doInitialization(Module &M) override;
182 bool runOnFunction(Function &F) override;
183 bool doFinalization(Module &M) override;
Anton Korobeynikov19edda02010-07-24 21:52:08 +0000184
Mehdi Amini117296c2016-10-01 02:56:57 +0000185 StringRef getPassName() const override { return "Merge internal globals"; }
Anton Korobeynikov19edda02010-07-24 21:52:08 +0000186
Craig Topper3e4c6972014-03-05 09:10:37 +0000187 void getAnalysisUsage(AnalysisUsage &AU) const override {
Anton Korobeynikov19edda02010-07-24 21:52:08 +0000188 AU.setPreservesCFG();
189 FunctionPass::getAnalysisUsage(AU);
190 }
Anton Korobeynikov19edda02010-07-24 21:52:08 +0000191 };
192} // end anonymous namespace
193
Devang Patel76c85632011-10-17 17:17:43 +0000194char GlobalMerge::ID = 0;
Eric Christophered47b222015-02-23 19:28:45 +0000195INITIALIZE_PASS_BEGIN(GlobalMerge, "global-merge", "Merge global variables",
196 false, false)
197INITIALIZE_PASS_END(GlobalMerge, "global-merge", "Merge global variables",
198 false, false)
Devang Patel76c85632011-10-17 17:17:43 +0000199
200bool GlobalMerge::doMerge(SmallVectorImpl<GlobalVariable*> &Globals,
Silviu Barangaa055aab2013-01-07 12:31:25 +0000201 Module &M, bool isConst, unsigned AddrSpace) const {
Mehdi Aminif6727b02015-07-07 18:49:25 +0000202 auto &DL = M.getDataLayout();
Anton Korobeynikov19edda02010-07-24 21:52:08 +0000203 // FIXME: Find better heuristics
David Blaikie9ed57a92015-08-21 22:00:44 +0000204 std::stable_sort(Globals.begin(), Globals.end(),
205 [&DL](const GlobalVariable *GV1, const GlobalVariable *GV2) {
206 return DL.getTypeAllocSize(GV1->getValueType()) <
207 DL.getTypeAllocSize(GV2->getValueType());
208 });
Anton Korobeynikov19edda02010-07-24 21:52:08 +0000209
Ahmed Bougacha279e3ee2015-04-18 01:21:58 +0000210 // If we want to just blindly group all globals together, do so.
211 if (!GlobalMergeGroupByUse) {
212 BitVector AllGlobals(Globals.size());
213 AllGlobals.set();
214 return doMerge(Globals, AllGlobals, M, isConst, AddrSpace);
215 }
216
217 // If we want to be smarter, look at all uses of each global, to try to
218 // discover all sets of globals used together, and how many times each of
Benjamin Kramerdf005cb2015-08-08 18:27:36 +0000219 // these sets occurred.
Ahmed Bougacha279e3ee2015-04-18 01:21:58 +0000220 //
221 // Keep this reasonably efficient, by having an append-only list of all sets
222 // discovered so far (UsedGlobalSet), and mapping each "together-ness" unit of
223 // code (currently, a Function) to the set of globals seen so far that are
224 // used together in that unit (GlobalUsesByFunction).
225 //
226 // When we look at the Nth global, we now that any new set is either:
227 // - the singleton set {N}, containing this global only, or
228 // - the union of {N} and a previously-discovered set, containing some
229 // combination of the previous N-1 globals.
230 // Using that knowledge, when looking at the Nth global, we can keep:
231 // - a reference to the singleton set {N} (CurGVOnlySetIdx)
232 // - a list mapping each previous set to its union with {N} (EncounteredUGS),
233 // if it actually occurs.
234
235 // We keep track of the sets of globals used together "close enough".
236 struct UsedGlobalSet {
237 UsedGlobalSet(size_t Size) : Globals(Size), UsageCount(1) {}
238 BitVector Globals;
239 unsigned UsageCount;
240 };
241
242 // Each set is unique in UsedGlobalSets.
243 std::vector<UsedGlobalSet> UsedGlobalSets;
244
245 // Avoid repeating the create-global-set pattern.
246 auto CreateGlobalSet = [&]() -> UsedGlobalSet & {
247 UsedGlobalSets.emplace_back(Globals.size());
248 return UsedGlobalSets.back();
249 };
250
251 // The first set is the empty set.
252 CreateGlobalSet().UsageCount = 0;
253
254 // We define "close enough" to be "in the same function".
255 // FIXME: Grouping uses by function is way too aggressive, so we should have
256 // a better metric for distance between uses.
257 // The obvious alternative would be to group by BasicBlock, but that's in
258 // turn too conservative..
259 // Anything in between wouldn't be trivial to compute, so just stick with
260 // per-function grouping.
261
262 // The value type is an index into UsedGlobalSets.
263 // The default (0) conveniently points to the empty set.
264 DenseMap<Function *, size_t /*UsedGlobalSetIdx*/> GlobalUsesByFunction;
265
266 // Now, look at each merge-eligible global in turn.
267
268 // Keep track of the sets we already encountered to which we added the
269 // current global.
270 // Each element matches the same-index element in UsedGlobalSets.
271 // This lets us efficiently tell whether a set has already been expanded to
272 // include the current global.
273 std::vector<size_t> EncounteredUGS;
274
275 for (size_t GI = 0, GE = Globals.size(); GI != GE; ++GI) {
276 GlobalVariable *GV = Globals[GI];
277
278 // Reset the encountered sets for this global...
279 std::fill(EncounteredUGS.begin(), EncounteredUGS.end(), 0);
280 // ...and grow it in case we created new sets for the previous global.
281 EncounteredUGS.resize(UsedGlobalSets.size());
282
283 // We might need to create a set that only consists of the current global.
284 // Keep track of its index into UsedGlobalSets.
285 size_t CurGVOnlySetIdx = 0;
286
287 // For each global, look at all its Uses.
288 for (auto &U : GV->uses()) {
289 // This Use might be a ConstantExpr. We're interested in Instruction
290 // users, so look through ConstantExpr...
291 Use *UI, *UE;
292 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(U.getUser())) {
Oliver Stannard8379e292015-06-08 16:55:31 +0000293 if (CE->use_empty())
294 continue;
Ahmed Bougacha279e3ee2015-04-18 01:21:58 +0000295 UI = &*CE->use_begin();
296 UE = nullptr;
297 } else if (isa<Instruction>(U.getUser())) {
298 UI = &U;
299 UE = UI->getNext();
300 } else {
301 continue;
302 }
303
304 // ...to iterate on all the instruction users of the global.
305 // Note that we iterate on Uses and not on Users to be able to getNext().
306 for (; UI != UE; UI = UI->getNext()) {
307 Instruction *I = dyn_cast<Instruction>(UI->getUser());
308 if (!I)
309 continue;
310
311 Function *ParentFn = I->getParent()->getParent();
Ahmed Bougacha82076412015-06-04 20:39:23 +0000312
313 // If we're only optimizing for size, ignore non-minsize functions.
Sanjay Patel1cd6d882015-08-18 16:44:23 +0000314 if (OnlyOptimizeForSize && !ParentFn->optForMinSize())
Ahmed Bougacha82076412015-06-04 20:39:23 +0000315 continue;
316
Ahmed Bougacha279e3ee2015-04-18 01:21:58 +0000317 size_t UGSIdx = GlobalUsesByFunction[ParentFn];
318
319 // If this is the first global the basic block uses, map it to the set
320 // consisting of this global only.
321 if (!UGSIdx) {
322 // If that set doesn't exist yet, create it.
323 if (!CurGVOnlySetIdx) {
324 CurGVOnlySetIdx = UsedGlobalSets.size();
325 CreateGlobalSet().Globals.set(GI);
326 } else {
327 ++UsedGlobalSets[CurGVOnlySetIdx].UsageCount;
328 }
329
330 GlobalUsesByFunction[ParentFn] = CurGVOnlySetIdx;
331 continue;
332 }
333
334 // If we already encountered this BB, just increment the counter.
335 if (UsedGlobalSets[UGSIdx].Globals.test(GI)) {
336 ++UsedGlobalSets[UGSIdx].UsageCount;
337 continue;
338 }
339
340 // If not, the previous set wasn't actually used in this function.
341 --UsedGlobalSets[UGSIdx].UsageCount;
342
343 // If we already expanded the previous set to include this global, just
344 // reuse that expanded set.
345 if (size_t ExpandedIdx = EncounteredUGS[UGSIdx]) {
346 ++UsedGlobalSets[ExpandedIdx].UsageCount;
347 GlobalUsesByFunction[ParentFn] = ExpandedIdx;
348 continue;
349 }
350
351 // If not, create a new set consisting of the union of the previous set
352 // and this global. Mark it as encountered, so we can reuse it later.
353 GlobalUsesByFunction[ParentFn] = EncounteredUGS[UGSIdx] =
354 UsedGlobalSets.size();
355
356 UsedGlobalSet &NewUGS = CreateGlobalSet();
357 NewUGS.Globals.set(GI);
358 NewUGS.Globals |= UsedGlobalSets[UGSIdx].Globals;
359 }
360 }
361 }
362
363 // Now we found a bunch of sets of globals used together. We accumulated
364 // the number of times we encountered the sets (i.e., the number of blocks
365 // that use that exact set of globals).
366 //
367 // Multiply that by the size of the set to give us a crude profitability
368 // metric.
369 std::sort(UsedGlobalSets.begin(), UsedGlobalSets.end(),
370 [](const UsedGlobalSet &UGS1, const UsedGlobalSet &UGS2) {
371 return UGS1.Globals.count() * UGS1.UsageCount <
372 UGS2.Globals.count() * UGS2.UsageCount;
373 });
374
375 // We can choose to merge all globals together, but ignore globals never used
376 // with another global. This catches the obviously non-profitable cases of
377 // having a single global, but is aggressive enough for any other case.
378 if (GlobalMergeIgnoreSingleUse) {
379 BitVector AllGlobals(Globals.size());
380 for (size_t i = 0, e = UsedGlobalSets.size(); i != e; ++i) {
381 const UsedGlobalSet &UGS = UsedGlobalSets[e - i - 1];
382 if (UGS.UsageCount == 0)
383 continue;
384 if (UGS.Globals.count() > 1)
385 AllGlobals |= UGS.Globals;
386 }
387 return doMerge(Globals, AllGlobals, M, isConst, AddrSpace);
388 }
389
390 // Starting from the sets with the best (=biggest) profitability, find a
391 // good combination.
392 // The ideal (and expensive) solution can only be found by trying all
393 // combinations, looking for the one with the best profitability.
394 // Don't be smart about it, and just pick the first compatible combination,
395 // starting with the sets with the best profitability.
396 BitVector PickedGlobals(Globals.size());
397 bool Changed = false;
398
399 for (size_t i = 0, e = UsedGlobalSets.size(); i != e; ++i) {
400 const UsedGlobalSet &UGS = UsedGlobalSets[e - i - 1];
401 if (UGS.UsageCount == 0)
402 continue;
403 if (PickedGlobals.anyCommon(UGS.Globals))
404 continue;
405 PickedGlobals |= UGS.Globals;
406 // If the set only contains one global, there's no point in merging.
407 // Ignore the global for inclusion in other sets though, so keep it in
408 // PickedGlobals.
409 if (UGS.Globals.count() < 2)
410 continue;
411 Changed |= doMerge(Globals, UGS.Globals, M, isConst, AddrSpace);
412 }
413
414 return Changed;
415}
416
David Blaikie47bf5c02015-08-21 22:19:06 +0000417bool GlobalMerge::doMerge(const SmallVectorImpl<GlobalVariable *> &Globals,
Ahmed Bougacha279e3ee2015-04-18 01:21:58 +0000418 const BitVector &GlobalSet, Module &M, bool isConst,
419 unsigned AddrSpace) const {
David Blaikie47bf5c02015-08-21 22:19:06 +0000420 assert(Globals.size() > 1);
Ahmed Bougacha279e3ee2015-04-18 01:21:58 +0000421
Chris Lattner229907c2011-07-18 04:54:35 +0000422 Type *Int32Ty = Type::getInt32Ty(M.getContext());
Mehdi Aminif6727b02015-07-07 18:49:25 +0000423 auto &DL = M.getDataLayout();
Anton Korobeynikov19edda02010-07-24 21:52:08 +0000424
Ahmed Bougacha279e3ee2015-04-18 01:21:58 +0000425 DEBUG(dbgs() << " Trying to merge set, starts with #"
426 << GlobalSet.find_first() << "\n");
427
428 ssize_t i = GlobalSet.find_first();
429 while (i != -1) {
430 ssize_t j = 0;
Anton Korobeynikov19edda02010-07-24 21:52:08 +0000431 uint64_t MergedSize = 0;
Jay Foadb804a2b2011-07-12 14:06:48 +0000432 std::vector<Type*> Tys;
Anton Korobeynikov19edda02010-07-24 21:52:08 +0000433 std::vector<Constant*> Inits;
Jiangning Liub2ae37f2014-06-11 06:44:53 +0000434
Adrian Prantl554fd992016-11-11 17:50:09 +0000435 bool HasExternal = false;
Adrian Prantl622bddb2016-11-11 22:09:25 +0000436 StringRef FirstExternalName;
Ahmed Bougacha279e3ee2015-04-18 01:21:58 +0000437 for (j = i; j != -1; j = GlobalSet.find_next(j)) {
David Blaikie9ed57a92015-08-21 22:00:44 +0000438 Type *Ty = Globals[j]->getValueType();
Mehdi Aminif6727b02015-07-07 18:49:25 +0000439 MergedSize += DL.getTypeAllocSize(Ty);
Bob Wilson4c8ab192010-11-17 21:25:36 +0000440 if (MergedSize > MaxOffset) {
441 break;
442 }
Anton Korobeynikov19edda02010-07-24 21:52:08 +0000443 Tys.push_back(Ty);
444 Inits.push_back(Globals[j]->getInitializer());
Adrian Prantl554fd992016-11-11 17:50:09 +0000445
446 if (Globals[j]->hasExternalLinkage() && !HasExternal) {
447 HasExternal = true;
Adrian Prantl622bddb2016-11-11 22:09:25 +0000448 FirstExternalName = Globals[j]->getName();
Adrian Prantl554fd992016-11-11 17:50:09 +0000449 }
Anton Korobeynikov19edda02010-07-24 21:52:08 +0000450 }
451
Adrian Prantl554fd992016-11-11 17:50:09 +0000452 // If merged variables doesn't have external linkage, we needn't to expose
453 // the symbol after merging.
454 GlobalValue::LinkageTypes Linkage = HasExternal
455 ? GlobalValue::ExternalLinkage
456 : GlobalValue::InternalLinkage;
Chris Lattnere40007a2010-09-05 21:18:45 +0000457 StructType *MergedTy = StructType::get(M.getContext(), Tys);
458 Constant *MergedInit = ConstantStruct::get(MergedTy, Inits);
Jiangning Liub2ae37f2014-06-11 06:44:53 +0000459
Adrian Prantl6cb849e2016-11-11 21:48:09 +0000460 // On Darwin external linkage needs to be preserved, otherwise
461 // dsymutil cannot preserve the debug info for the merged
462 // variables. If they have external linkage, use the symbol name
463 // of the first variable merged as the suffix of global symbol
464 // name. This avoids a link-time naming conflict for the
465 // _MergedGlobals symbols.
Adrian Prantl554fd992016-11-11 17:50:09 +0000466 Twine MergedName =
467 (IsMachO && HasExternal)
Adrian Prantl622bddb2016-11-11 22:09:25 +0000468 ? "_MergedGlobals_" + FirstExternalName
Adrian Prantl554fd992016-11-11 17:50:09 +0000469 : "_MergedGlobals";
470 auto MergedLinkage = IsMachO ? Linkage : GlobalValue::PrivateLinkage;
471 auto *MergedGV = new GlobalVariable(
472 M, MergedTy, isConst, MergedLinkage, MergedInit, MergedName, nullptr,
473 GlobalVariable::NotThreadLocal, AddrSpace);
Jiangning Liub2ae37f2014-06-11 06:44:53 +0000474
Peter Collingbourned4135bb2016-09-13 01:12:59 +0000475 const StructLayout *MergedLayout = DL.getStructLayout(MergedTy);
476
David Blaikie6614d8d2015-09-14 20:29:26 +0000477 for (ssize_t k = i, idx = 0; k != j; k = GlobalSet.find_next(k), ++idx) {
Jiangning Liub2ae37f2014-06-11 06:44:53 +0000478 GlobalValue::LinkageTypes Linkage = Globals[k]->getLinkage();
479 std::string Name = Globals[k]->getName();
480
Peter Collingbourned4135bb2016-09-13 01:12:59 +0000481 // Copy metadata while adjusting any debug info metadata by the original
482 // global's offset within the merged global.
483 MergedGV->copyMetadata(Globals[k], MergedLayout->getElementOffset(idx));
484
Chris Lattnere40007a2010-09-05 21:18:45 +0000485 Constant *Idx[2] = {
486 ConstantInt::get(Int32Ty, 0),
David Blaikie6614d8d2015-09-14 20:29:26 +0000487 ConstantInt::get(Int32Ty, idx),
Chris Lattnere40007a2010-09-05 21:18:45 +0000488 };
David Blaikie4a2e73b2015-04-02 18:55:32 +0000489 Constant *GEP =
490 ConstantExpr::getInBoundsGetElementPtr(MergedTy, MergedGV, Idx);
Anton Korobeynikov19edda02010-07-24 21:52:08 +0000491 Globals[k]->replaceAllUsesWith(GEP);
492 Globals[k]->eraseFromParent();
Jiangning Liub2ae37f2014-06-11 06:44:53 +0000493
John Brawn0bef27d2015-08-12 13:36:48 +0000494 // When the linkage is not internal we must emit an alias for the original
495 // variable name as it may be accessed from another object. On non-Mach-O
496 // we can also emit an alias for internal linkage as it's safe to do so.
497 // It's not safe on Mach-O as the alias (and thus the portion of the
498 // MergedGlobals variable) may be dead stripped at link time.
Peter Collingbournefe12d0e2016-05-19 04:38:56 +0000499 if (Linkage != GlobalValue::InternalLinkage || !IsMachO) {
David Blaikie6614d8d2015-09-14 20:29:26 +0000500 GlobalAlias::create(Tys[idx], AddrSpace, Linkage, Name, GEP, &M);
John Brawn0bef27d2015-08-12 13:36:48 +0000501 }
Jiangning Liub2ae37f2014-06-11 06:44:53 +0000502
Devang Patel76c85632011-10-17 17:17:43 +0000503 NumMerged++;
Anton Korobeynikov19edda02010-07-24 21:52:08 +0000504 }
505 i = j;
506 }
507
508 return true;
509}
510
Quentin Colombet8fc34092013-03-18 22:30:07 +0000511void GlobalMerge::collectUsedGlobalVariables(Module &M) {
512 // Extract global variables from llvm.used array
513 const GlobalVariable *GV = M.getGlobalVariable("llvm.used");
514 if (!GV || !GV->hasInitializer()) return;
515
516 // Should be an array of 'i8*'.
Rafael Espindola74f2e462013-04-22 14:58:02 +0000517 const ConstantArray *InitList = cast<ConstantArray>(GV->getInitializer());
518
Quentin Colombet8fc34092013-03-18 22:30:07 +0000519 for (unsigned i = 0, e = InitList->getNumOperands(); i != e; ++i)
520 if (const GlobalVariable *G =
521 dyn_cast<GlobalVariable>(InitList->getOperand(i)->stripPointerCasts()))
522 MustKeepGlobalVariables.insert(G);
523}
524
525void GlobalMerge::setMustKeepGlobalVariables(Module &M) {
Quentin Colombet8fc34092013-03-18 22:30:07 +0000526 collectUsedGlobalVariables(M);
527
Reid Klecknerf8d1d122016-10-19 19:56:22 +0000528 for (Function &F : M) {
529 for (BasicBlock &BB : F) {
530 Instruction *Pad = BB.getFirstNonPHI();
531 if (!Pad->isEHPad())
532 continue;
Quentin Colombet8fc34092013-03-18 22:30:07 +0000533
Reid Klecknerf8d1d122016-10-19 19:56:22 +0000534 // Keep globals used by landingpads and catchpads.
535 for (const Use &U : Pad->operands()) {
Quentin Colombet8fc34092013-03-18 22:30:07 +0000536 if (const GlobalVariable *GV =
Reid Klecknerf8d1d122016-10-19 19:56:22 +0000537 dyn_cast<GlobalVariable>(U->stripPointerCasts()))
Quentin Colombet8fc34092013-03-18 22:30:07 +0000538 MustKeepGlobalVariables.insert(GV);
Reid Klecknerf8d1d122016-10-19 19:56:22 +0000539 }
Quentin Colombet8fc34092013-03-18 22:30:07 +0000540 }
541 }
542}
Anton Korobeynikov19edda02010-07-24 21:52:08 +0000543
Devang Patel76c85632011-10-17 17:17:43 +0000544bool GlobalMerge::doInitialization(Module &M) {
Tim Northoverf804c172014-02-18 11:17:29 +0000545 if (!EnableGlobalMerge)
546 return false;
547
Peter Collingbournefe12d0e2016-05-19 04:38:56 +0000548 IsMachO = Triple(M.getTargetTriple()).isOSBinFormatMachO();
549
Mehdi Aminif6727b02015-07-07 18:49:25 +0000550 auto &DL = M.getDataLayout();
Silviu Barangaa055aab2013-01-07 12:31:25 +0000551 DenseMap<unsigned, SmallVector<GlobalVariable*, 16> > Globals, ConstGlobals,
552 BSSGlobals;
Anton Korobeynikov19edda02010-07-24 21:52:08 +0000553 bool Changed = false;
Quentin Colombet8fc34092013-03-18 22:30:07 +0000554 setMustKeepGlobalVariables(M);
Anton Korobeynikov19edda02010-07-24 21:52:08 +0000555
556 // Grab all non-const globals.
Duncan P. N. Exon Smith530d0402015-10-09 18:57:47 +0000557 for (auto &GV : M.globals()) {
Jiangning Liub2ae37f2014-06-11 06:44:53 +0000558 // Merge is safe for "normal" internal or external globals only
Duncan P. N. Exon Smith530d0402015-10-09 18:57:47 +0000559 if (GV.isDeclaration() || GV.isThreadLocal() || GV.hasSection())
Jiangning Liub2ae37f2014-06-11 06:44:53 +0000560 continue;
561
Duncan P. N. Exon Smith530d0402015-10-09 18:57:47 +0000562 if (!(MergeExternalGlobals && GV.hasExternalLinkage()) &&
563 !GV.hasInternalLinkage())
Anton Korobeynikov19edda02010-07-24 21:52:08 +0000564 continue;
565
Duncan P. N. Exon Smith530d0402015-10-09 18:57:47 +0000566 PointerType *PT = dyn_cast<PointerType>(GV.getType());
Silviu Barangaa055aab2013-01-07 12:31:25 +0000567 assert(PT && "Global variable is not a pointer!");
568
569 unsigned AddressSpace = PT->getAddressSpace();
570
Anton Korobeynikov19edda02010-07-24 21:52:08 +0000571 // Ignore fancy-aligned globals for now.
Duncan P. N. Exon Smith530d0402015-10-09 18:57:47 +0000572 unsigned Alignment = DL.getPreferredAlignment(&GV);
573 Type *Ty = GV.getValueType();
Mehdi Aminif6727b02015-07-07 18:49:25 +0000574 if (Alignment > DL.getABITypeAlignment(Ty))
Anton Korobeynikov19edda02010-07-24 21:52:08 +0000575 continue;
576
Anton Korobeynikov6bcea062010-07-26 18:45:39 +0000577 // Ignore all 'special' globals.
Duncan P. N. Exon Smith530d0402015-10-09 18:57:47 +0000578 if (GV.getName().startswith("llvm.") ||
579 GV.getName().startswith(".llvm."))
Anton Korobeynikov6bcea062010-07-26 18:45:39 +0000580 continue;
581
Quentin Colombet8fc34092013-03-18 22:30:07 +0000582 // Ignore all "required" globals:
Duncan P. N. Exon Smith530d0402015-10-09 18:57:47 +0000583 if (isMustKeepGlobalVariable(&GV))
Quentin Colombet8fc34092013-03-18 22:30:07 +0000584 continue;
585
Mehdi Aminif6727b02015-07-07 18:49:25 +0000586 if (DL.getTypeAllocSize(Ty) < MaxOffset) {
Peter Collingbournefe12d0e2016-05-19 04:38:56 +0000587 if (TM &&
588 TargetLoweringObjectFile::getKindForGlobal(&GV, *TM).isBSSLocal())
Duncan P. N. Exon Smith530d0402015-10-09 18:57:47 +0000589 BSSGlobals[AddressSpace].push_back(&GV);
590 else if (GV.isConstant())
591 ConstGlobals[AddressSpace].push_back(&GV);
Anton Korobeynikov19edda02010-07-24 21:52:08 +0000592 else
Duncan P. N. Exon Smith530d0402015-10-09 18:57:47 +0000593 Globals[AddressSpace].push_back(&GV);
Anton Korobeynikov19edda02010-07-24 21:52:08 +0000594 }
595 }
596
David Blaikie47bf5c02015-08-21 22:19:06 +0000597 for (auto &P : Globals)
598 if (P.second.size() > 1)
599 Changed |= doMerge(P.second, M, false, P.first);
Silviu Barangaa055aab2013-01-07 12:31:25 +0000600
David Blaikie47bf5c02015-08-21 22:19:06 +0000601 for (auto &P : BSSGlobals)
602 if (P.second.size() > 1)
603 Changed |= doMerge(P.second, M, false, P.first);
Bob Wilson881b45c2010-11-17 21:25:39 +0000604
David Blaikied4860002015-08-25 17:01:36 +0000605 if (EnableGlobalMergeOnConst)
606 for (auto &P : ConstGlobals)
607 if (P.second.size() > 1)
608 Changed |= doMerge(P.second, M, true, P.first);
Anton Korobeynikov19edda02010-07-24 21:52:08 +0000609
610 return Changed;
611}
612
Devang Patel76c85632011-10-17 17:17:43 +0000613bool GlobalMerge::runOnFunction(Function &F) {
Anton Korobeynikov19edda02010-07-24 21:52:08 +0000614 return false;
615}
616
Quentin Colombet2393cb92013-03-19 21:46:49 +0000617bool GlobalMerge::doFinalization(Module &M) {
618 MustKeepGlobalVariables.clear();
619 return false;
620}
621
Ahmed Bougacha82076412015-06-04 20:39:23 +0000622Pass *llvm::createGlobalMergePass(const TargetMachine *TM, unsigned Offset,
John Brawn8b954242015-08-03 12:08:41 +0000623 bool OnlyOptimizeForSize,
624 bool MergeExternalByDefault) {
625 bool MergeExternal = (EnableGlobalMergeOnExternal == cl::BOU_UNSET) ?
626 MergeExternalByDefault : (EnableGlobalMergeOnExternal == cl::BOU_TRUE);
627 return new GlobalMerge(TM, Offset, OnlyOptimizeForSize, MergeExternal);
Anton Korobeynikov19edda02010-07-24 21:52:08 +0000628}