Revert r204076 for now - it caused significant regressions in a number of

benchmarks.

<rdar://problem/16368461>



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@204558 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 78 insertions, 47 deletions

diff --git a/lib/Transforms/IPO/GlobalOpt.cpp b/lib/Transforms/IPO/GlobalOpt.cpp
index 06b31c6eb5..1a510cf4db 100644
--- a/lib/Transforms/IPO/GlobalOpt.cpp
+++ b/lib/Transforms/IPO/GlobalOpt.cpp
@@ -1588,16 +1588,18 @@ static bool OptimizeOnceStoredGlobal(GlobalVariable *GV, Value *StoredOnceVal,
   return false;
 }
 
-/// TryToAddRangeMetadata - At this point, we have learned that the only
+/// TryToShrinkGlobalToBoolean - At this point, we have learned that the only
 /// two values ever stored into GV are its initializer and OtherVal.  See if we
-/// can annotate loads from it with range metadata describing this.
-/// This exposes the values to other scalar optimizations.
-static bool TryToAddRangeMetadata(GlobalVariable *GV, Constant *OtherVal) {
+/// can shrink the global into a boolean and select between the two values
+/// whenever it is used.  This exposes the values to other scalar optimizations.
+static bool TryToShrinkGlobalToBoolean(GlobalVariable *GV, Constant *OtherVal) {
   Type *GVElType = GV->getType()->getElementType();
 
-  // If GVElType is already i1, it already has a minimal range. If the type of
-  // the GV is an FP value, pointer or vector, don't do this optimization
-  // because range metadata is currently only supported on scalar integers.
+  // If GVElType is already i1, it is already shrunk.  If the type of the GV is
+  // an FP value, pointer or vector, don't do this optimization because a select
+  // between them is very expensive and unlikely to lead to later
+  // simplification.  In these cases, we typically end up with "cond ? v1 : v2"
+  // where v1 and v2 both require constant pool loads, a big loss.
   if (GVElType == Type::getInt1Ty(GV->getContext()) ||
       GVElType->isFloatingPointTy() ||
       GVElType->isPointerTy() || GVElType->isVectorTy())
@@ -1609,53 +1611,81 @@ static bool TryToAddRangeMetadata(GlobalVariable *GV, Constant *OtherVal) {
     if (!isa<LoadInst>(U) && !isa<StoreInst>(U))
       return false;
 
+  DEBUG(dbgs() << "   *** SHRINKING TO BOOL: " << *GV);
+
+  // Create the new global, initializing it to false.
+  GlobalVariable *NewGV = new GlobalVariable(Type::getInt1Ty(GV->getContext()),
+                                             false,
+                                             GlobalValue::InternalLinkage,
+                                        ConstantInt::getFalse(GV->getContext()),
+                                             GV->getName()+".b",
+                                             GV->getThreadLocalMode(),
+                                             GV->getType()->getAddressSpace());
+  GV->getParent()->getGlobalList().insert(GV, NewGV);
+
   Constant *InitVal = GV->getInitializer();
   assert(InitVal->getType() != Type::getInt1Ty(GV->getContext()) &&
-         "No reason to add range metadata!");
+         "No reason to shrink to bool!");
 
-  // The MD_range metadata only supports absolute integer constants.
-  if (!isa<ConstantInt>(InitVal) || !isa<ConstantInt>(OtherVal))
-    return false;
+  // If initialized to zero and storing one into the global, we can use a cast
+  // instead of a select to synthesize the desired value.
+  bool IsOneZero = false;
+  if (ConstantInt *CI = dyn_cast<ConstantInt>(OtherVal))
+    IsOneZero = InitVal->isNullValue() && CI->isOne();
 
-  DEBUG(dbgs() << "   *** ADDING RANGE METADATA: " << *GV);
-
-  for (User *U : GV->users()) {
-    Instruction *UI = cast<Instruction>(U);
-    if (LoadInst *LI = dyn_cast<LoadInst>(UI)) {
-      // If we already have a range, don't add a new one, so that GlobalOpt
-      // terminates. In theory, we could merge the two ranges.
-      if (LI->getMetadata(LLVMContext::MD_range))
-        return false;
-      // Add range metadata to the load. Range metadata can represent multiple
-      // ranges, but they must be discontiguous, so we have two cases: the case
-      // where the values are adjacent, in which case we add one range, and the
-      // case where they're not, in which case we add two.
-      APInt Min = cast<ConstantInt>(InitVal)->getValue();
-      APInt Max = cast<ConstantInt>(OtherVal)->getValue();
-      if (Max.slt(Min))
-        std::swap(Min, Max);
-      APInt Min1 = Min + 1;
-      APInt Max1 = Max + 1;
-      if (Min1 == Max) {
-        Value *Vals[] = {
-          ConstantInt::get(GV->getContext(), Min),
-          ConstantInt::get(GV->getContext(), Max1),
-        };
-        MDNode *MD = MDNode::get(LI->getContext(), Vals);
-        LI->setMetadata(LLVMContext::MD_range, MD);
+  while (!GV->use_empty()) {
+    Instruction *UI = cast<Instruction>(GV->user_back());
+    if (StoreInst *SI = dyn_cast<StoreInst>(UI)) {
+      // Change the store into a boolean store.
+      bool StoringOther = SI->getOperand(0) == OtherVal;
+      // Only do this if we weren't storing a loaded value.
+      Value *StoreVal;
+      if (StoringOther || SI->getOperand(0) == InitVal) {
+        StoreVal = ConstantInt::get(Type::getInt1Ty(GV->getContext()),
+                                    StoringOther);
       } else {
-        Value *Vals[] = {
-          ConstantInt::get(GV->getContext(), Min),
-          ConstantInt::get(GV->getContext(), Min1),
-          ConstantInt::get(GV->getContext(), Max),
-          ConstantInt::get(GV->getContext(), Max1),
-        };
-        MDNode *MD = MDNode::get(LI->getContext(), Vals);
-        LI->setMetadata(LLVMContext::MD_range, MD);
+        // Otherwise, we are storing a previously loaded copy.  To do this,
+        // change the copy from copying the original value to just copying the
+        // bool.
+        Instruction *StoredVal = cast<Instruction>(SI->getOperand(0));
+
+        // If we've already replaced the input, StoredVal will be a cast or
+        // select instruction.  If not, it will be a load of the original
+        // global.
+        if (LoadInst *LI = dyn_cast<LoadInst>(StoredVal)) {
+          assert(LI->getOperand(0) == GV && "Not a copy!");
+          // Insert a new load, to preserve the saved value.
+          StoreVal = new LoadInst(NewGV, LI->getName()+".b", false, 0,
+                                  LI->getOrdering(), LI->getSynchScope(), LI);
+        } else {
+          assert((isa<CastInst>(StoredVal) || isa<SelectInst>(StoredVal)) &&
+                 "This is not a form that we understand!");
+          StoreVal = StoredVal->getOperand(0);
+          assert(isa<LoadInst>(StoreVal) && "Not a load of NewGV!");
+        }
       }
+      new StoreInst(StoreVal, NewGV, false, 0,
+                    SI->getOrdering(), SI->getSynchScope(), SI);
+    } else {
+      // Change the load into a load of bool then a select.
+      LoadInst *LI = cast<LoadInst>(UI);
+      LoadInst *NLI = new LoadInst(NewGV, LI->getName()+".b", false, 0,
+                                   LI->getOrdering(), LI->getSynchScope(), LI);
+      Value *NSI;
+      if (IsOneZero)
+        NSI = new ZExtInst(NLI, LI->getType(), "", LI);
+      else
+        NSI = SelectInst::Create(NLI, OtherVal, InitVal, "", LI);
+      NSI->takeName(LI);
+      LI->replaceAllUsesWith(NSI);
     }
+    UI->eraseFromParent();
   }
 
+  // Retain the name of the old global variable. People who are debugging their
+  // programs may expect these variables to be named the same.
+  NewGV->takeName(GV);
+  GV->eraseFromParent();
   return true;
 }
 
@@ -1809,10 +1839,11 @@ bool GlobalOpt::ProcessInternalGlobal(GlobalVariable *GV,
                                  DL, TLI))
       return true;
 
-    // Otherwise, if the global was not a boolean, we can add range metadata.
+    // Otherwise, if the global was not a boolean, we can shrink it to be a
+    // boolean.
     if (Constant *SOVConstant = dyn_cast<Constant>(GS.StoredOnceValue)) {
       if (GS.Ordering == NotAtomic) {
-        if (TryToAddRangeMetadata(GV, SOVConstant)) {
+        if (TryToShrinkGlobalToBoolean(GV, SOVConstant)) {
           ++NumShrunkToBool;
           return true;
         }