Add basic support for performing whole-function RLE.

Note: This has not yet been thoroughly tested.  Use at your own risk.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@40489 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/Analysis/MemoryDependenceAnalysis.h

@@ -38,7 +38,8 @@ class MemoryDependenceAnalysis : public FunctionPass {
   
     Instruction* getCallSiteDependency(CallSite C, Instruction* start,
                                        bool local = true);
-    SmallPtrSet<Instruction*, 4> nonLocalHelper(Instruction* query, BasicBlock* block);
+    bool nonLocalHelper(Instruction* query, BasicBlock* block,
+                        DenseMap<BasicBlock*, Value*>& resp);
   public:
     
     static Instruction* NonLocal;
@@ -67,7 +68,8 @@ class MemoryDependenceAnalysis : public FunctionPass {
     Instruction* getDependency(Instruction* query, Instruction* start = 0,
                                BasicBlock* block = 0);
     
-    SmallPtrSet<Instruction*, 4> getNonLocalDependency(Instruction* query);
+    bool getNonLocalDependency(Instruction* query,
+                               DenseMap<BasicBlock*, Value*>& resp);
     
     /// removeInstruction - Remove an instruction from the dependence analysis,
     /// updating the dependence of instructions that previously depended on it.

lib/Analysis/MemoryDependenceAnalysis.cpp

@@ -26,8 +26,8 @@ using namespace llvm;
 
 char MemoryDependenceAnalysis::ID = 0;
   
-Instruction* MemoryDependenceAnalysis::NonLocal = (Instruction*)0;
-Instruction* MemoryDependenceAnalysis::None = (Instruction*)(~0 - 1);
+Instruction* MemoryDependenceAnalysis::NonLocal = (Instruction*)-2;
+Instruction* MemoryDependenceAnalysis::None = (Instruction*)-3;
   
 // Register this pass...
 static RegisterPass<MemoryDependenceAnalysis> X("memdep",
@@ -101,52 +101,49 @@ Instruction* MemoryDependenceAnalysis::getCallSiteDependency(CallSite C, Instruc
   return NonLocal;
 }
 
-SmallPtrSet<Instruction*, 4> MemoryDependenceAnalysis::nonLocalHelper(Instruction* query,
-                                                                      BasicBlock* block) {
-  SmallPtrSet<Instruction*, 4> ret;
+bool MemoryDependenceAnalysis::nonLocalHelper(Instruction* query,
+                                              BasicBlock* block,
+                                              DenseMap<BasicBlock*, Value*>& resp) {
+  if (resp.count(block))
+    return resp[block] != None;
   
-  Instruction* localDep = getDependency(query, block->end(), block);
+  Instruction* localDep = getDependency(query, 0, block);
   if (localDep != NonLocal) {
-    ret.insert(localDep);
-    return ret;
+    resp.insert(std::make_pair(block, localDep));
+    return true;
   }
   
+  bool inserted = false;
   for (pred_iterator PI = pred_begin(block), PE = pred_end(block);
-       PI != PE; ++PI) {
-    SmallPtrSet<Instruction*, 4> pred_deps = nonLocalHelper(query, *PI);
-    for (SmallPtrSet<Instruction*, 4>::iterator I = pred_deps.begin(),
-         E = pred_deps.end(); I != E; ++I)
-      ret.insert(*I);
-  }
+       PI != PE; ++PI)
+    inserted |= nonLocalHelper(query, *PI, resp);
   
-  if (ret.empty())
-    ret.insert(None);
+  if (!inserted)
+    resp.insert(std::make_pair(block, None));
   
-  return ret;
+  return inserted;
 }
 
-SmallPtrSet<Instruction*, 4> MemoryDependenceAnalysis::getNonLocalDependency(Instruction* query) {
-  SmallPtrSet<Instruction*, 4> ret;
-  
+bool MemoryDependenceAnalysis::getNonLocalDependency(Instruction* query,
+                                                     DenseMap<BasicBlock*, Value*>& resp) {
   Instruction* localDep = getDependency(query);
   if (localDep != NonLocal) {
-    ret.insert(localDep);
-    return ret;
+    resp.insert(std::make_pair(query->getParent(), localDep));
+    return true;
   }
   
+  bool inserted = false;
+  
   BasicBlock* parent = query->getParent();
   for (pred_iterator PI = pred_begin(parent), PE = pred_end(parent);
        PI != PE; ++PI) {
-    SmallPtrSet<Instruction*, 4> pred_deps = nonLocalHelper(query, *PI);
-    for (SmallPtrSet<Instruction*, 4>::iterator I = pred_deps.begin(),
-         E = pred_deps.end(); I != E; ++I)
-      ret.insert(*I);
+    inserted |= nonLocalHelper(query, *PI, resp);
   }
   
-  if (ret.empty())
-    ret.insert(None);
+  if (!inserted)
+    resp.insert(std::make_pair(query->getParent(), None));
   
-  return ret;
+  return inserted;
 }
 
 /// getDependency - Return the instruction on which a memory operation
@@ -163,12 +160,14 @@ Instruction* MemoryDependenceAnalysis::getDependency(Instruction* query,
   // If we have a _confirmed_ cached entry, return it
   if (cachedResult.second)
     return cachedResult.first;
-  else if (cachedResult.first != NonLocal)
+  else if (cachedResult.first && cachedResult.first != NonLocal)
   // If we have an unconfirmed cached entry, we can start our search from there
     QI = cachedResult.first;
   
   if (start)
     QI = start;
+  else if (!start && block)
+    QI = block->end();
   
   AliasAnalysis& AA = getAnalysis<AliasAnalysis>();
   TargetData& TD = getAnalysis<TargetData>();
@@ -212,7 +211,7 @@ Instruction* MemoryDependenceAnalysis::getDependency(Instruction* query,
     if (StoreInst* S = dyn_cast<StoreInst>(QI)) {
       // All volatile loads/stores depend on each other
       if (queryIsVolatile && S->isVolatile()) {
-        if (!start) {
+        if (!start || block) {
           depGraphLocal.insert(std::make_pair(query, std::make_pair(S, true)));
           reverseDep.insert(std::make_pair(S, query));
         }
@@ -225,7 +224,7 @@ Instruction* MemoryDependenceAnalysis::getDependency(Instruction* query,
     } else if (LoadInst* L = dyn_cast<LoadInst>(QI)) {
       // All volatile loads/stores depend on each other
       if (queryIsVolatile && L->isVolatile()) {
-        if (!start) {
+        if (!start || block) {
           depGraphLocal.insert(std::make_pair(query, std::make_pair(L, true)));
           reverseDep.insert(std::make_pair(L, query));
         }
@@ -253,7 +252,7 @@ Instruction* MemoryDependenceAnalysis::getDependency(Instruction* query,
       // Call insts need special handling.  Check is they can modify our pointer
       if (AA.getModRefInfo(CallSite::get(QI), dependee, dependeeSize) !=
           AliasAnalysis::NoModRef) {
-        if (!start) {
+        if (!start || block) {
           depGraphLocal.insert(std::make_pair(query, std::make_pair(QI, true)));
           reverseDep.insert(std::make_pair(QI, query));
         }
@@ -270,7 +269,7 @@ Instruction* MemoryDependenceAnalysis::getDependency(Instruction* query,
                                               dependee, dependeeSize);
       
       if (R != AliasAnalysis::NoAlias) {
-        if (!start) {
+        if (!start || block) {
           depGraphLocal.insert(std::make_pair(query, std::make_pair(QI, true)));
           reverseDep.insert(std::make_pair(QI, query));
         }
@@ -281,7 +280,7 @@ Instruction* MemoryDependenceAnalysis::getDependency(Instruction* query,
   }
   
   // If we found nothing, return the non-local flag
-  if (!start) {
+  if (!start || block) {
     depGraphLocal.insert(std::make_pair(query,
                                         std::make_pair(NonLocal, true)));
     reverseDep.insert(std::make_pair(NonLocal, query));

lib/Transforms/Scalar/GVN.cpp

@@ -15,6 +15,7 @@
 #define DEBUG_TYPE "gvn"
 #include "llvm/Value.h"
 #include "llvm/Transforms/Scalar.h"
+#include "llvm/BasicBlock.h"
 #include "llvm/Instructions.h"
 #include "llvm/Function.h"
 #include "llvm/DerivedTypes.h"
@@ -648,6 +649,10 @@ namespace {
                             ValueNumberedSet& currAvail,
                             DenseMap<Value*, LoadInst*>& lastSeenLoad,
                             SmallVector<Instruction*, 4>& toErase);
+    bool processNonLocalLoad(LoadInst* L, SmallVector<Instruction*, 4>& toErase);
+    Value *performPHIConstruction(BasicBlock *BB, LoadInst* orig,
+                                  DenseMap<BasicBlock*, Value*> &Phis);
+    void dump(DenseMap<BasicBlock*, Value*>& d);
   };
   
   char GVN::ID = 0;
@@ -687,6 +692,88 @@ void GVN::val_insert(ValueNumberedSet& s, Value* v) {
     s.insert(v);
 }
 
+void GVN::dump(DenseMap<BasicBlock*, Value*>& d) {
+  printf("{\n");
+  for (DenseMap<BasicBlock*, Value*>::iterator I = d.begin(),
+       E = d.end(); I != E; ++I) {
+    if (I->second == MemoryDependenceAnalysis::None)
+      printf("None\n");
+    else
+      I->second->dump();
+  }
+  printf("}\n");
+}
+
+
+Value *GVN::performPHIConstruction(BasicBlock *BB, LoadInst* orig,
+                                   DenseMap<BasicBlock*, Value*> &Phis) {
+  DenseMap<BasicBlock*, Value*>::iterator DI = Phis.find(BB);
+  if (DI != Phis.end())
+    return DI->second;
+  
+  unsigned numPreds = std::distance(pred_begin(BB), pred_end(BB));
+  
+  if (numPreds == 1) {
+    Phis[BB] = Phis[*pred_begin(BB)];
+    return Phis[BB];
+  } else {
+    PHINode *PN = new PHINode(orig->getType(), orig->getName()+".rle", BB->begin());
+    PN->reserveOperandSpace(numPreds);
+                                 
+    // Fill in the incoming values for the block.
+    for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
+      PN->addIncoming(performPHIConstruction(*PI, orig, Phis), *PI);
+    
+    bool all_same = PN->getNumIncomingValues() != 1;
+    Value* first = PN->getIncomingValue(0);
+    for (unsigned i = 1; i < PN->getNumIncomingValues(); ++i)
+      all_same &= (PN->getIncomingValue(i) == first);
+    
+    if (all_same) {
+      PN->eraseFromParent();
+      return first;
+    } else {
+      return PN;
+    }
+  }
+}
+
+bool GVN::processNonLocalLoad(LoadInst* L, SmallVector<Instruction*, 4>& toErase) {
+  MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
+  
+  DenseMap<BasicBlock*, Value*> deps;
+  bool ret = MD.getNonLocalDependency(L, deps);
+  if (!ret)
+    return false;
+  
+  DenseMap<BasicBlock*, Value*> repl;
+  for (DenseMap<BasicBlock*, Value*>::iterator I = deps.begin(), E = deps.end();
+       I != E; ++I)
+    if (I->second == MemoryDependenceAnalysis::None) {
+      return false;
+    } else if (StoreInst* S = dyn_cast<StoreInst>(I->second)) {
+      if (S->getPointerOperand() == L->getPointerOperand())
+        repl.insert(std::make_pair(I->first, S->getOperand(0)));
+      else
+        return false;
+    } else if (LoadInst* LD = dyn_cast<LoadInst>(I->second)) {
+      if (LD->getPointerOperand() == L->getPointerOperand())
+        repl.insert(std::make_pair(I->first, LD));
+      else
+        return false;
+    } else {
+      return false;
+    }
+  
+  Value* v = performPHIConstruction(L->getParent(), L, repl);
+  
+  MD.removeInstruction(L);
+  L->replaceAllUsesWith(v);
+  toErase.push_back(L);
+
+  return true;
+}
+
 bool GVN::processLoad(LoadInst* L,
                          DenseMap<Value*, LoadInst*>& lastLoad,
                          SmallVector<Instruction*, 4>& toErase) {
@@ -701,6 +788,9 @@ bool GVN::processLoad(LoadInst* L,
   // ... to a pointer that has been loaded from before...
   MemoryDependenceAnalysis& MD = getAnalysis<MemoryDependenceAnalysis>();
   Instruction* dep = MD.getDependency(L);
+  if (dep == MemoryDependenceAnalysis::NonLocal &&
+      L->getParent() != &L->getParent()->getParent()->getEntryBlock())
+    processNonLocalLoad(L, toErase);
   bool deletedLoad = false;
   
   while (dep != MemoryDependenceAnalysis::None &&
@@ -802,15 +892,17 @@ bool GVN::runOnFunction(Function &F) {
 
     for (BasicBlock::iterator BI = BB->begin(), BE = BB->end();
          BI != BE; ++BI) {
-      processInstruction(BI, currAvail, lastSeenLoad, toErase);
+      changed_function |= processInstruction(BI, currAvail, lastSeenLoad, toErase);
+      
+      NumGVNInstr += toErase.size();
+      
+      for (SmallVector<Instruction*, 4>::iterator I = toErase.begin(),
+           E = toErase.end(); I != E; ++I)
+        (*I)->eraseFromParent();
+      
+      toErase.clear();
     }
   }
   
-  NumGVNInstr = toErase.size();
-  
-  for (SmallVector<Instruction*, 4>::iterator I = toErase.begin(),
-       E = toErase.end(); I != E; ++I)
-    (*I)->eraseFromParent();
-  
   return changed_function;
 }

test/Transforms/GVN/dominated.ll

@@ -0,0 +1,20 @@
+; RUN: llvm-as < %s | opt -gvn | llvm-dis | not grep DEAD
+
+define i32 @main(i32** %p) {
+block1:
+  %z = load i32** %p
+	br i1 true, label %block2, label %block3
+
+block2:
+ %a = load i32** %p
+ br label %block4
+
+block3:
+  %b = load i32** %p
+  br label %block4
+
+block4:
+  %DEAD = load i32** %p
+  %c = load i32* %DEAD
+  ret i32 %c
+}

test/Transforms/GVN/nonlocal.ll

@@ -0,0 +1,19 @@
+; RUN: llvm-as < %s | opt -gvn | llvm-dis | not grep {DEAD =}
+
+define i32 @main(i32** %p) {
+block1:
+	br i1 true, label %block2, label %block3
+
+block2:
+ %a = load i32** %p
+ br label %block4
+
+block3:
+  %b = load i32** %p
+  br label %block4
+
+block4:
+  %DEAD = load i32** %p
+  %c = load i32* %DEAD
+  ret i32 %c
+}

test/Transforms/GVN/semidominated.ll

@@ -0,0 +1,19 @@
+; RUN: llvm-as < %s | opt -gvn | llvm-dis | not grep {DEAD =}
+
+define i32 @main(i32* %p) {
+block1:
+  %z = load i32* %p
+	br i1 true, label %block2, label %block3
+
+block2:
+ br label %block4
+
+block3:
+  %b = bitcast i32 0 to i32
+  store i32 %b, i32* %p
+  br label %block4
+
+block4:
+  %DEAD = load i32* %p
+  ret i32 %DEAD
+}