svn mv Target/ARM/ARMGlobalMerge.cpp Transforms/Scalar/GlobalMerge.cpp
There is no reason to have simple IR level pass in lib/Target.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@142200 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/Scalar/GlobalMerge.cpp b/lib/Transforms/Scalar/GlobalMerge.cpp
new file mode 100644
index 0000000..0772b48
--- /dev/null
+++ b/lib/Transforms/Scalar/GlobalMerge.cpp
@@ -0,0 +1,226 @@
+//===-- GlobalMerge.cpp - Internal globals merging -----------------------===//
+//
+// The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+// This pass merges globals with internal linkage into one. This way all the
+// globals which were merged into a biggest one can be addressed using offsets
+// from the same base pointer (no need for separate base pointer for each of the
+// global). Such a transformation can significantly reduce the register pressure
+// when many globals are involved.
+//
+// For example, consider the code which touches several global variables at
+// once:
+//
+// static int foo[N], bar[N], baz[N];
+//
+// for (i = 0; i < N; ++i) {
+// foo[i] = bar[i] * baz[i];
+// }
+//
+// On ARM the addresses of 3 arrays should be kept in the registers, thus
+// this code has quite large register pressure (loop body):
+//
+// ldr r1, [r5], #4
+// ldr r2, [r6], #4
+// mul r1, r2, r1
+// str r1, [r0], #4
+//
+// Pass converts the code to something like:
+//
+// static struct {
+// int foo[N];
+// int bar[N];
+// int baz[N];
+// } merged;
+//
+// for (i = 0; i < N; ++i) {
+// merged.foo[i] = merged.bar[i] * merged.baz[i];
+// }
+//
+// and in ARM code this becomes:
+//
+// ldr r0, [r5, #40]
+// ldr r1, [r5, #80]
+// mul r0, r1, r0
+// str r0, [r5], #4
+//
+// note that we saved 2 registers here almostly "for free".
+// ===---------------------------------------------------------------------===//
+
+#define DEBUG_TYPE "global-merge"
+#include "llvm/Transforms/Scalar.h"
+#include "llvm/Attributes.h"
+#include "llvm/Constants.h"
+#include "llvm/DerivedTypes.h"
+#include "llvm/Function.h"
+#include "llvm/GlobalVariable.h"
+#include "llvm/Instructions.h"
+#include "llvm/Intrinsics.h"
+#include "llvm/Module.h"
+#include "llvm/Pass.h"
+#include "llvm/Target/TargetData.h"
+#include "llvm/Target/TargetLowering.h"
+#include "llvm/Target/TargetLoweringObjectFile.h"
+#include "llvm/ADT/Statistic.h"
+using namespace llvm;
+
+STATISTIC(NumMerged , "Number of globals merged");
+namespace {
+ class GlobalMerge : public FunctionPass {
+ /// TLI - Keep a pointer of a TargetLowering to consult for determining
+ /// target type sizes.
+ const TargetLowering *TLI;
+
+ bool doMerge(SmallVectorImpl<GlobalVariable*> &Globals,
+ Module &M, bool isConst) const;
+
+ public:
+ static char ID; // Pass identification, replacement for typeid.
+ explicit GlobalMerge(const TargetLowering *tli = 0)
+ : FunctionPass(ID), TLI(tli) {
+ initializeGlobalMergePass(*PassRegistry::getPassRegistry());
+ }
+
+ virtual bool doInitialization(Module &M);
+ virtual bool runOnFunction(Function &F);
+
+ const char *getPassName() const {
+ return "Merge internal globals";
+ }
+
+ virtual void getAnalysisUsage(AnalysisUsage &AU) const {
+ AU.setPreservesCFG();
+ FunctionPass::getAnalysisUsage(AU);
+ }
+
+ struct GlobalCmp {
+ const TargetData *TD;
+
+ GlobalCmp(const TargetData *td) : TD(td) { }
+
+ bool operator()(const GlobalVariable *GV1, const GlobalVariable *GV2) {
+ Type *Ty1 = cast<PointerType>(GV1->getType())->getElementType();
+ Type *Ty2 = cast<PointerType>(GV2->getType())->getElementType();
+
+ return (TD->getTypeAllocSize(Ty1) < TD->getTypeAllocSize(Ty2));
+ }
+ };
+ };
+} // end anonymous namespace
+
+char GlobalMerge::ID = 0;
+INITIALIZE_PASS(GlobalMerge, "global-merge",
+ "Global Merge", false, false)
+
+
+bool GlobalMerge::doMerge(SmallVectorImpl<GlobalVariable*> &Globals,
+ Module &M, bool isConst) const {
+ const TargetData *TD = TLI->getTargetData();
+
+ // FIXME: Infer the maximum possible offset depending on the actual users
+ // (these max offsets are different for the users inside Thumb or ARM
+ // functions)
+ unsigned MaxOffset = TLI->getMaximalGlobalOffset();
+
+ // FIXME: Find better heuristics
+ std::stable_sort(Globals.begin(), Globals.end(), GlobalCmp(TD));
+
+ Type *Int32Ty = Type::getInt32Ty(M.getContext());
+
+ for (size_t i = 0, e = Globals.size(); i != e; ) {
+ size_t j = 0;
+ uint64_t MergedSize = 0;
+ std::vector<Type*> Tys;
+ std::vector<Constant*> Inits;
+ for (j = i; j != e; ++j) {
+ Type *Ty = Globals[j]->getType()->getElementType();
+ MergedSize += TD->getTypeAllocSize(Ty);
+ if (MergedSize > MaxOffset) {
+ break;
+ }
+ Tys.push_back(Ty);
+ Inits.push_back(Globals[j]->getInitializer());
+ }
+
+ StructType *MergedTy = StructType::get(M.getContext(), Tys);
+ Constant *MergedInit = ConstantStruct::get(MergedTy, Inits);
+ GlobalVariable *MergedGV = new GlobalVariable(M, MergedTy, isConst,
+ GlobalValue::InternalLinkage,
+ MergedInit, "_MergedGlobals");
+ for (size_t k = i; k < j; ++k) {
+ Constant *Idx[2] = {
+ ConstantInt::get(Int32Ty, 0),
+ ConstantInt::get(Int32Ty, k-i)
+ };
+ Constant *GEP = ConstantExpr::getInBoundsGetElementPtr(MergedGV, Idx);
+ Globals[k]->replaceAllUsesWith(GEP);
+ Globals[k]->eraseFromParent();
+ NumMerged++;
+ }
+ i = j;
+ }
+
+ return true;
+}
+
+
+bool GlobalMerge::doInitialization(Module &M) {
+ SmallVector<GlobalVariable*, 16> Globals, ConstGlobals, BSSGlobals;
+ const TargetData *TD = TLI->getTargetData();
+ unsigned MaxOffset = TLI->getMaximalGlobalOffset();
+ bool Changed = false;
+
+ // Grab all non-const globals.
+ for (Module::global_iterator I = M.global_begin(),
+ E = M.global_end(); I != E; ++I) {
+ // Merge is safe for "normal" internal globals only
+ if (!I->hasLocalLinkage() || I->isThreadLocal() || I->hasSection())
+ continue;
+
+ // Ignore fancy-aligned globals for now.
+ unsigned Alignment = I->getAlignment();
+ Type *Ty = I->getType()->getElementType();
+ if (Alignment > TD->getABITypeAlignment(Ty))
+ continue;
+
+ // Ignore all 'special' globals.
+ if (I->getName().startswith("llvm.") ||
+ I->getName().startswith(".llvm."))
+ continue;
+
+ if (TD->getTypeAllocSize(Ty) < MaxOffset) {
+ const TargetLoweringObjectFile &TLOF = TLI->getObjFileLowering();
+ if (TLOF.getKindForGlobal(I, TLI->getTargetMachine()).isBSSLocal())
+ BSSGlobals.push_back(I);
+ else if (I->isConstant())
+ ConstGlobals.push_back(I);
+ else
+ Globals.push_back(I);
+ }
+ }
+
+ if (Globals.size() > 1)
+ Changed |= doMerge(Globals, M, false);
+ if (BSSGlobals.size() > 1)
+ Changed |= doMerge(BSSGlobals, M, false);
+
+ // 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);
+
+ return Changed;
+}
+
+bool GlobalMerge::runOnFunction(Function &F) {
+ return false;
+}
+
+Pass *llvm::createGlobalMergePass(const TargetLowering *tli) {
+ return new GlobalMerge(tli);
+}