Extend global merge pass to optionally consider global constant variables.
Also add some checks to not merge globals used within landing pad instructions or marked as "used".
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@177331 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/Scalar/GlobalMerge.cpp b/lib/Transforms/Scalar/GlobalMerge.cpp
index 1601a8d..14e463a 100644
--- a/lib/Transforms/Scalar/GlobalMerge.cpp
+++ b/lib/Transforms/Scalar/GlobalMerge.cpp
@@ -53,6 +53,7 @@
#define DEBUG_TYPE "global-merge"
#include "llvm/Transforms/Scalar.h"
+#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/IR/Attributes.h"
#include "llvm/IR/Constants.h"
@@ -60,14 +61,22 @@
#include "llvm/IR/DerivedTypes.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/GlobalVariable.h"
+#include "llvm/IR/InlineAsm.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/Intrinsics.h"
+#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/Module.h"
#include "llvm/Pass.h"
+#include "llvm/Support/CommandLine.h"
#include "llvm/Target/TargetLowering.h"
#include "llvm/Target/TargetLoweringObjectFile.h"
using namespace llvm;
+static cl::opt<bool>
+EnableGlobalMergeOnConst("global-merge-on-const", cl::Hidden,
+ cl::desc("Enable global merge pass on constants"),
+ cl::init(false));
+
STATISTIC(NumMerged , "Number of globals merged");
namespace {
class GlobalMerge : public FunctionPass {
@@ -78,6 +87,23 @@
bool doMerge(SmallVectorImpl<GlobalVariable*> &Globals,
Module &M, bool isConst, unsigned AddrSpace) const;
+ /// \brief Check if the given variable has been identified as must keep
+ /// \pre setMustKeepGlobalVariables must have been called on the Module that
+ /// contains GV
+ bool isMustKeepGlobalVariable(const GlobalVariable *GV) const {
+ return MustKeepGlobalVariables.count(GV);
+ }
+
+ /// Collect every variables marked as "used" or used in a landing pad
+ /// instruction for this Module.
+ void setMustKeepGlobalVariables(Module &M);
+
+ /// Collect every variables marked as "used"
+ void collectUsedGlobalVariables(Module &M);
+
+ /// Keep track of the GlobalVariable that are marked as "used"
+ SmallPtrSet<const GlobalVariable *, 16> MustKeepGlobalVariables;
+
public:
static char ID; // Pass identification, replacement for typeid.
explicit GlobalMerge(const TargetLowering *tli = 0)
@@ -169,6 +195,46 @@
return true;
}
+void GlobalMerge::collectUsedGlobalVariables(Module &M) {
+ // Extract global variables from llvm.used array
+ const GlobalVariable *GV = M.getGlobalVariable("llvm.used");
+ if (!GV || !GV->hasInitializer()) return;
+
+ // Should be an array of 'i8*'.
+ const ConstantArray *InitList = dyn_cast<ConstantArray>(GV->getInitializer());
+ if (InitList == 0) return;
+
+ for (unsigned i = 0, e = InitList->getNumOperands(); i != e; ++i)
+ if (const GlobalVariable *G =
+ dyn_cast<GlobalVariable>(InitList->getOperand(i)->stripPointerCasts()))
+ MustKeepGlobalVariables.insert(G);
+}
+
+void GlobalMerge::setMustKeepGlobalVariables(Module &M) {
+ // If we already processed a Module, UsedGlobalVariables may have been
+ // populated. Reset the information for this module.
+ MustKeepGlobalVariables.clear();
+ collectUsedGlobalVariables(M);
+
+ for (Module::iterator IFn = M.begin(), IEndFn = M.end(); IFn != IEndFn;
+ ++IFn) {
+ for (Function::iterator IBB = IFn->begin(), IEndBB = IFn->end();
+ IBB != IEndBB; ++IBB) {
+ // Follow the inwoke link to find the landing pad instruction
+ const InvokeInst *II = dyn_cast<InvokeInst>(IBB->getTerminator());
+ if (!II) continue;
+
+ const LandingPadInst *LPInst = II->getUnwindDest()->getLandingPadInst();
+ // Look for globals in the clauses of the landing pad instruction
+ for (unsigned Idx = 0, NumClauses = LPInst->getNumClauses();
+ Idx != NumClauses; ++Idx)
+ if (const GlobalVariable *GV =
+ dyn_cast<GlobalVariable>(LPInst->getClause(Idx)
+ ->stripPointerCasts()))
+ MustKeepGlobalVariables.insert(GV);
+ }
+ }
+}
bool GlobalMerge::doInitialization(Module &M) {
DenseMap<unsigned, SmallVector<GlobalVariable*, 16> > Globals, ConstGlobals,
@@ -176,6 +242,7 @@
const DataLayout *TD = TLI->getDataLayout();
unsigned MaxOffset = TLI->getMaximalGlobalOffset();
bool Changed = false;
+ setMustKeepGlobalVariables(M);
// Grab all non-const globals.
for (Module::global_iterator I = M.global_begin(),
@@ -200,6 +267,12 @@
I->getName().startswith(".llvm."))
continue;
+ // Ignore all "required" globals:
+ // - the ones used for EH
+ // - the ones marked with "used" attribute
+ if (isMustKeepGlobalVariable(I))
+ continue;
+
if (TD->getTypeAllocSize(Ty) < MaxOffset) {
if (TargetLoweringObjectFile::getKindForGlobal(I, TLI->getTargetMachine())
.isBSSLocal())
@@ -221,11 +294,11 @@
if (I->second.size() > 1)
Changed |= doMerge(I->second, M, false, I->first);
- // FIXME: This currently breaks the EH processing due to way how the
- // typeinfo detection works. We might want to detect the TIs and ignore
- // them in the future.
- // if (ConstGlobals.size() > 1)
- // Changed |= doMerge(ConstGlobals, M, true);
+ if (EnableGlobalMergeOnConst)
+ for (DenseMap<unsigned, SmallVector<GlobalVariable*, 16> >::iterator
+ I = ConstGlobals.begin(), E = ConstGlobals.end(); I != E; ++I)
+ if (I->second.size() > 1)
+ Changed |= doMerge(I->second, M, true, I->first);
return Changed;
}