#define DEBUG_TYPE "constmerge"
#include "llvm/Transforms/IPO.h"
-#include "llvm/Constants.h"
-#include "llvm/DerivedTypes.h"
-#include "llvm/Module.h"
-#include "llvm/Pass.h"
#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/PointerIntPair.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/Statistic.h"
+#include "llvm/IR/Constants.h"
+#include "llvm/IR/DataLayout.h"
+#include "llvm/IR/DerivedTypes.h"
+#include "llvm/IR/Module.h"
+#include "llvm/Pass.h"
using namespace llvm;
STATISTIC(NumMerged, "Number of global constants merged");
initializeConstantMergePass(*PassRegistry::getPassRegistry());
}
- // run - For this pass, process all of the globals in the module,
- // eliminating duplicate constants.
- //
+ // For this pass, process all of the globals in the module, eliminating
+ // duplicate constants.
bool runOnModule(Module &M);
+
+ // Return true iff we can determine the alignment of this global variable.
+ bool hasKnownAlignment(GlobalVariable *GV) const;
+
+ // Return the alignment of the global, including converting the default
+ // alignment to a concrete value.
+ unsigned getAlignment(GlobalVariable *GV) const;
+
+ const DataLayout *TD;
};
}
UsedValues.insert(GV);
}
+// True if A is better than B.
+static bool IsBetterCannonical(const GlobalVariable &A,
+ const GlobalVariable &B) {
+ if (!A.hasLocalLinkage() && B.hasLocalLinkage())
+ return true;
+
+ if (A.hasLocalLinkage() && !B.hasLocalLinkage())
+ return false;
+
+ return A.hasUnnamedAddr();
+}
+
+bool ConstantMerge::hasKnownAlignment(GlobalVariable *GV) const {
+ return TD || GV->getAlignment() != 0;
+}
+
+unsigned ConstantMerge::getAlignment(GlobalVariable *GV) const {
+ if (TD)
+ return TD->getPreferredAlignment(GV);
+ return GV->getAlignment();
+}
+
bool ConstantMerge::runOnModule(Module &M) {
+ TD = getAnalysisIfAvailable<DataLayout>();
+
// Find all the globals that are marked "used". These cannot be merged.
SmallPtrSet<const GlobalValue*, 8> UsedGlobals;
FindUsedValues(M.getGlobalVariable("llvm.used"), UsedGlobals);
FindUsedValues(M.getGlobalVariable("llvm.compiler.used"), UsedGlobals);
- // Map unique constant/section pairs to globals. We don't want to merge
- // globals in different sections.
- DenseMap<Constant*, GlobalVariable*> CMap;
+ // Map unique <constants, has-unknown-alignment> pairs to globals. We don't
+ // want to merge globals of unknown alignment with those of explicit
+ // alignment. If we have DataLayout, we always know the alignment.
+ DenseMap<PointerIntPair<Constant*, 1, bool>, GlobalVariable*> CMap;
// Replacements - This vector contains a list of replacements to perform.
SmallVector<std::pair<GlobalVariable*, GlobalVariable*>, 32> Replacements;
// second level constants have initializers which point to the globals that
// were just merged.
while (1) {
- // First pass: identify all globals that can be merged together, filling in
- // the Replacements vector. We cannot do the replacement in this pass
- // because doing so may cause initializers of other globals to be rewritten,
- // invalidating the Constant* pointers in CMap.
- //
+
+ // First: Find the canonical constants others will be merged with.
for (Module::global_iterator GVI = M.global_begin(), E = M.global_end();
GVI != E; ) {
GlobalVariable *GV = GVI++;
-
+
// If this GV is dead, remove it.
GV->removeDeadConstantUsers();
if (GV->use_empty() && GV->hasLocalLinkage()) {
GV->eraseFromParent();
continue;
}
-
+
// Only process constants with initializers in the default address space.
if (!GV->isConstant() || !GV->hasDefinitiveInitializer() ||
GV->getType()->getAddressSpace() != 0 || GV->hasSection() ||
// Don't touch values marked with attribute(used).
UsedGlobals.count(GV))
continue;
-
- // Start by filling slots with only the globals we aren't allowed to
- // delete because they're externally visible.
- if (GV->hasLocalLinkage())
+
+ // This transformation is legal for weak ODR globals in the sense it
+ // doesn't change semantics, but we really don't want to perform it
+ // anyway; it's likely to pessimize code generation, and some tools
+ // (like the Darwin linker in cases involving CFString) don't expect it.
+ if (GV->isWeakForLinker())
continue;
-
+
Constant *Init = GV->getInitializer();
// Check to see if the initializer is already known.
- GlobalVariable *&Slot = CMap[Init];
+ PointerIntPair<Constant*, 1, bool> Pair(Init, hasKnownAlignment(GV));
+ GlobalVariable *&Slot = CMap[Pair];
- if (Slot == 0) { // Nope, add it to the map.
+ // If this is the first constant we find or if the old one is local,
+ // replace with the current one. If the current is externally visible
+ // it cannot be replace, but can be the canonical constant we merge with.
+ if (Slot == 0 || IsBetterCannonical(*GV, *Slot))
Slot = GV;
- }
}
+ // Second: identify all globals that can be merged together, filling in
+ // the Replacements vector. We cannot do the replacement in this pass
+ // because doing so may cause initializers of other globals to be rewritten,
+ // invalidating the Constant* pointers in CMap.
for (Module::global_iterator GVI = M.global_begin(), E = M.global_end();
GVI != E; ) {
GlobalVariable *GV = GVI++;
UsedGlobals.count(GV))
continue;
- // Only look at the remaining globals now.
+ // We can only replace constant with local linkage.
if (!GV->hasLocalLinkage())
continue;
Constant *Init = GV->getInitializer();
// Check to see if the initializer is already known.
- GlobalVariable *&Slot = CMap[Init];
+ PointerIntPair<Constant*, 1, bool> Pair(Init, hasKnownAlignment(GV));
+ GlobalVariable *Slot = CMap[Pair];
- if (Slot == 0) { // Nope, add it to the map.
- Slot = GV;
- } else { // Yup, this is a duplicate!
- // Make all uses of the duplicate constant use the canonical version.
- Replacements.push_back(std::make_pair(GV, Slot));
- }
+ if (!Slot || Slot == GV)
+ continue;
+
+ if (!Slot->hasUnnamedAddr() && !GV->hasUnnamedAddr())
+ continue;
+
+ if (!GV->hasUnnamedAddr())
+ Slot->setUnnamedAddr(false);
+
+ // Make all uses of the duplicate constant use the canonical version.
+ Replacements.push_back(std::make_pair(GV, Slot));
}
if (Replacements.empty())
// now. This avoid invalidating the pointers in CMap, which are unneeded
// now.
for (unsigned i = 0, e = Replacements.size(); i != e; ++i) {
+ // Bump the alignment if necessary.
+ if (Replacements[i].first->getAlignment() ||
+ Replacements[i].second->getAlignment()) {
+ Replacements[i].second->setAlignment(std::max(
+ Replacements[i].first->getAlignment(),
+ Replacements[i].second->getAlignment()));
+ }
+
// Eliminate any uses of the dead global.
Replacements[i].first->replaceAllUsesWith(Replacements[i].second);
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