Teach GlobalOpt to handle atomic accesses to globals.

 * Most of the transforms come through intact by having each transformed load or
store copy the ordering and synchronization scope of the original.
 * The transform that turns a global only accessed in main() into an alloca
(since main is non-recursive) with a store of the initial value uses an
unordered store, since it's guaranteed to be the first thing to happen in main.
(Threads may have started before main (!) but they can't have the address of a
function local before the point in the entry block we insert our code.)
 * The heap-SRoA transforms are disabled in the face of atomic operations. This
can probably be improved; it seems odd to have atomic accesses to an alloca
that doesn't have its address taken.

AnalyzeGlobal keeps track of the strongest ordering found in any use of the
global. This is more information than we need right now, but it's cheap to
compute and likely to be useful.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@149847 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 40 insertions, 13 deletions

diff --git a/lib/Transforms/IPO/GlobalOpt.cpp b/lib/Transforms/IPO/GlobalOpt.cpp
index 50f13255cd..3ec6348471 100644
--- a/lib/Transforms/IPO/GlobalOpt.cpp
+++ b/lib/Transforms/IPO/GlobalOpt.cpp
@@ -148,14 +148,27 @@ struct GlobalStatus {
   /// HasPHIUser - Set to true if this global has a user that is a PHI node.
   bool HasPHIUser;
 
+  /// AtomicOrdering - Set to the strongest atomic ordering requirement.
+  AtomicOrdering Ordering;
+
   GlobalStatus() : isCompared(false), isLoaded(false), StoredType(NotStored),
                    StoredOnceValue(0), AccessingFunction(0),
-                   HasMultipleAccessingFunctions(false), HasNonInstructionUser(false),
-                   HasPHIUser(false) {}
+                   HasMultipleAccessingFunctions(false),
+                   HasNonInstructionUser(false), HasPHIUser(false),
+                   Ordering(NotAtomic) {}
 };
 
 }
 
+/// StrongerOrdering - Return the stronger of the two ordering. If the two
+/// orderings are acquire and release, then return AcquireRelease.
+///
+static AtomicOrdering StrongerOrdering(AtomicOrdering X, AtomicOrdering Y) {
+  if (X == Acquire && Y == Release) return AcquireRelease;
+  if (Y == Acquire && X == Release) return AcquireRelease;
+  return (AtomicOrdering)std::max(X, Y);
+}
+
 /// SafeToDestroyConstant - It is safe to destroy a constant iff it is only used
 /// by constants itself.  Note that constants cannot be cyclic, so this test is
 /// pretty easy to implement recursively.
@@ -200,14 +213,16 @@ static bool AnalyzeGlobal(const Value *V, GlobalStatus &GS,
       }
       if (const LoadInst *LI = dyn_cast<LoadInst>(I)) {
         GS.isLoaded = true;
-        // Don't hack on volatile/atomic loads.
-        if (!LI->isSimple()) return true;
+        // Don't hack on volatile loads.
+        if (LI->isVolatile()) return true;
+        GS.Ordering = StrongerOrdering(GS.Ordering, LI->getOrdering());
       } else if (const StoreInst *SI = dyn_cast<StoreInst>(I)) {
         // Don't allow a store OF the address, only stores TO the address.
         if (SI->getOperand(0) == V) return true;
 
-        // Don't hack on volatile/atomic stores.
-        if (!SI->isSimple()) return true;
+        // Don't hack on volatile stores.
+        if (SI->isVolatile()) return true;
+        GS.Ordering = StrongerOrdering(GS.Ordering, SI->getOrdering());
 
         // If this is a direct store to the global (i.e., the global is a scalar
         // value, not an aggregate), keep more specific information about
@@ -879,7 +894,8 @@ static GlobalVariable *OptimizeGlobalAddressOfMalloc(GlobalVariable *GV,
   while (!GV->use_empty()) {
     if (StoreInst *SI = dyn_cast<StoreInst>(GV->use_back())) {
       // The global is initialized when the store to it occurs.
-      new StoreInst(ConstantInt::getTrue(GV->getContext()), InitBool, SI);
+      new StoreInst(ConstantInt::getTrue(GV->getContext()), InitBool, false, 0,
+                    SI->getOrdering(), SI->getSynchScope(), SI);
       SI->eraseFromParent();
       continue;
     }
@@ -894,7 +910,10 @@ static GlobalVariable *OptimizeGlobalAddressOfMalloc(GlobalVariable *GV,
 
       ICmpInst *ICI = cast<ICmpInst>(LoadUse.getUser());
       // Replace the cmp X, 0 with a use of the bool value.
-      Value *LV = new LoadInst(InitBool, InitBool->getName()+".val", ICI);
+      // Sink the load to where the compare was, if atomic rules allow us to.
+      Value *LV = new LoadInst(InitBool, InitBool->getName()+".val", false, 0,
+                               LI->getOrdering(), LI->getSynchScope(),
+                               LI->isUnordered() ? (Instruction*)ICI : LI);
       InitBoolUsed = true;
       switch (ICI->getPredicate()) {
       default: llvm_unreachable("Unknown ICmp Predicate!");
@@ -1454,6 +1473,7 @@ static GlobalVariable *PerformHeapAllocSRoA(GlobalVariable *GV, CallInst *CI,
 static bool TryToOptimizeStoreOfMallocToGlobal(GlobalVariable *GV,
                                                CallInst *CI,
                                                Type *AllocTy,
+                                               AtomicOrdering Ordering,
                                                Module::global_iterator &GVI,
                                                TargetData *TD) {
   if (!TD)
@@ -1503,6 +1523,9 @@ static bool TryToOptimizeStoreOfMallocToGlobal(GlobalVariable *GV,
   // into multiple malloc'd arrays, one for each field.  This is basically
   // SRoA for malloc'd memory.
 
+  if (Ordering != NotAtomic)
+    return false;
+
   // If this is an allocation of a fixed size array of structs, analyze as a
   // variable size array.  malloc [100 x struct],1 -> malloc struct, 100
   if (NElems == ConstantInt::get(CI->getArgOperand(0)->getType(), 1))
@@ -1545,6 +1568,7 @@ static bool TryToOptimizeStoreOfMallocToGlobal(GlobalVariable *GV,
 // OptimizeOnceStoredGlobal - Try to optimize globals based on the knowledge
 // that only one value (besides its initializer) is ever stored to the global.
 static bool OptimizeOnceStoredGlobal(GlobalVariable *GV, Value *StoredOnceVal,
+                                     AtomicOrdering Ordering,
                                      Module::global_iterator &GVI,
                                      TargetData *TD) {
   // Ignore no-op GEPs and bitcasts.
@@ -1566,7 +1590,7 @@ static bool OptimizeOnceStoredGlobal(GlobalVariable *GV, Value *StoredOnceVal,
     } else if (CallInst *CI = extractMallocCall(StoredOnceVal)) {
       Type *MallocType = getMallocAllocatedType(CI);
       if (MallocType && TryToOptimizeStoreOfMallocToGlobal(GV, CI, MallocType,
-                                                           GVI, TD))
+                                                           Ordering, GVI, TD))
         return true;
     }
   }
@@ -1642,7 +1666,8 @@ static bool TryToShrinkGlobalToBoolean(GlobalVariable *GV, Constant *OtherVal) {
         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", LI);
+          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!");
@@ -1650,11 +1675,13 @@ static bool TryToShrinkGlobalToBoolean(GlobalVariable *GV, Constant *OtherVal) {
           assert(isa<LoadInst>(StoreVal) && "Not a load of NewGV!");
         }
       }
-      new StoreInst(StoreVal, NewGV, SI);
+      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", LI);
+      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);
@@ -1808,7 +1835,7 @@ bool GlobalOpt::ProcessInternalGlobal(GlobalVariable *GV,
 
     // Try to optimize globals based on the knowledge that only one value
     // (besides its initializer) is ever stored to the global.
-    if (OptimizeOnceStoredGlobal(GV, GS.StoredOnceValue, GVI,
+    if (OptimizeOnceStoredGlobal(GV, GS.StoredOnceValue, GS.Ordering, GVI,
                                  getAnalysisIfAvailable<TargetData>()))
       return true;