From: Peizhao Ou <peizhaoo@uci.edu>
Date: Fri, 13 Apr 2018 17:05:47 +0000 (-0700)
Subject: Adds address dependency for atomic loads (for relaxed load l, if any subsequent relax... 
X-Git-Url: http://plrg.eecs.uci.edu/git/?a=commitdiff_plain;h=e82814b6938222a5e6e56c2f7fc24504c2573d71;p=oota-llvm.git

Adds address dependency for atomic loads (for relaxed load l, if any subsequent relaxed load depends on l, we don't need to taint l)
---

diff --git a/lib/CodeGen/CodeGenPrepare.cpp b/lib/CodeGen/CodeGenPrepare.cpp
index f4ff3787e63..7674e5cff92 100644
--- a/lib/CodeGen/CodeGenPrepare.cpp
+++ b/lib/CodeGen/CodeGenPrepare.cpp
@@ -221,6 +221,7 @@ FunctionPass *llvm::createCodeGenPreparePass(const TargetMachine *TM) {
 namespace {
 
 bool StoreAddressDependOnValue(StoreInst* SI, Value* DepVal);
+bool LoadAddressDependOnValue(LoadInst* LI, Value* DepVal);
 Value* GetUntaintedAddress(Value* CurrentAddress);
 
 // The depth we trace down a variable to look for its dependence set.
@@ -935,6 +936,49 @@ Instruction* findMostRecentDependenceUsage(LoadInst* LI, Instruction* LaterInst,
   return usage_inst;
 }
 
+// XXX-comment: For relaxed load 'LI', and the first upcoming store/conditional
+// branch instruction 'FirstInst', returns whether there are any intermediate
+// instructions I (including 'FirstInst') that satisfy:
+// 1. I is a load/store, and its address depends on 'LI'.
+// 2. I is a conditional branch whose condition depends on 'LI'.
+// Note that 'LI' and 'FirstInst' can be in different basic blocks, but LI's
+// basic block can unconditionally jumps (by steps) to FirstInst's block.
+bool NeedExtraConstraints(LoadInst* LI, Instruction* FirstInst) {
+  if (!FirstInst) {
+    return true;
+  }
+  auto* BB = LI->getParent();
+  auto BBI = LI->getIterator();
+  BBI++;
+  while (true) {
+    auto* I = &*BBI;
+    BBI++;
+    BranchInst *BI = dyn_cast<BranchInst>(I);
+    if (BI && BI->isUnconditional()) {
+      BasicBlock *DestBB = BI->getSuccessor(0);
+      BBI = DestBB->begin();
+      continue;
+    }
+
+    if (I->getOpcode() == Instruction::Store) {
+      return !StoreAddressDependOnValue(dyn_cast<StoreInst>(I), LI);
+    } else if (I->getOpcode() == Instruction::Load) {
+      if (I->isAtomic() &&
+          LoadAddressDependOnValue(dyn_cast<LoadInst>(I), LI)) {
+        // Normal loads are subject to be reordered by the backend, so we only
+        // rely on atomic loads.
+        return false;
+      }
+    } else if (I->getOpcode() == Instruction::Br) {
+      return !ConditionalBranchDependsOnValue(dyn_cast<BranchInst>(I), LI);
+    }
+    if (I == FirstInst) {
+      return true;
+    }
+  }
+  return true;
+}
+
 // XXX-comment: Returns whether the code has been changed.
 bool AddFakeConditionalBranchAfterMonotonicLoads(
     SmallSet<LoadInst*, 1>& MonotonicLoadInsts, DominatorTree* DT) {
@@ -944,24 +988,10 @@ bool AddFakeConditionalBranchAfterMonotonicLoads(
     MonotonicLoadInsts.erase(LI);
     SmallVector<BasicBlock*, 2> ChainedBB;
     auto* FirstInst = findFirstStoreCondBranchInst(LI, &ChainedBB);
-    if (FirstInst != nullptr) {
-      if (FirstInst->getOpcode() == Instruction::Store) {
-        if (StoreAddressDependOnValue(dyn_cast<StoreInst>(FirstInst), LI)) {
-          continue;
-        }
-      } else if (FirstInst->getOpcode() == Instruction::Br) {
-        if (ConditionalBranchDependsOnValue(dyn_cast<BranchInst>(FirstInst),
-                                            LI)) {
-          continue;
-        }
-      } else {
-        IntrinsicInst* II = dyn_cast<IntrinsicInst>(FirstInst);
-        if (!II || II->getIntrinsicID() != Intrinsic::aarch64_stlxr) {
-          dbgs() << "FirstInst=" << *FirstInst << "\n";
-          assert(false && "findFirstStoreCondBranchInst() should return a "
-                          "store/condition branch instruction");
-        }
-      }
+
+    // First check whether existing load-store ordering constraints exist.
+    if (FirstInst != nullptr && !NeedExtraConstraints(LI, FirstInst)) {
+      continue;
     }
 
     // We really need to process the relaxed load now.
@@ -1260,6 +1290,10 @@ bool StoreAddressDependOnValue(StoreInst* SI, Value* DepVal) {
   return dependenceSetInclusion(SI->getPointerOperand(), DepVal);
 }
 
+bool LoadAddressDependOnValue(LoadInst* LI, Value* DepVal) {
+  return dependenceSetInclusion(LI->getPointerOperand(), DepVal);
+}
+
 bool StoreDependOnValue(StoreInst* SI, Value* Dep) {
   return dependenceSetInclusion(SI, Dep);
 }