IR: De-duplicate code for replacing operands in place

[oota-llvm.git] / lib / Analysis / MemoryDependenceAnalysis.cpp

diff --git a/lib/Analysis/MemoryDependenceAnalysis.cpp b/lib/Analysis/MemoryDependenceAnalysis.cpp
index 5966937271940084fe9d4e0eecc9b0a132caa2d7..8f22b0ed3de3dd6dfd99ee49430ed9ea8d698715 100644 (file)
--- a/lib/Analysis/MemoryDependenceAnalysis.cpp
+++ b/lib/Analysis/MemoryDependenceAnalysis.cpp
@@ -407,10 +407,31 @@ getPointerDependencyFrom(const AliasAnalysis::Location &MemLoc, bool isLoad,
 
     // Values depend on loads if the pointers are must aliased.  This means that
     // a load depends on another must aliased load from the same value.
+    // One exception is atomic loads: a value can depend on an atomic load that it
+    // does not alias with when this atomic load indicates that another thread may
+    // be accessing the location.
     if (LoadInst *LI = dyn_cast<LoadInst>(Inst)) {
       // Atomic loads have complications involved.
+      // A monotonic load is OK if the query inst is itself not atomic.
       // FIXME: This is overly conservative.
-      if (!LI->isUnordered())
+      if (!LI->isUnordered()) {
+        if (!QueryInst)
+          return MemDepResult::getClobber(LI);
+        if (LI->getOrdering() != Monotonic)
+          return MemDepResult::getClobber(LI);
+        if (auto *QueryLI = dyn_cast<LoadInst>(QueryInst))
+          if (!QueryLI->isSimple())
+            return MemDepResult::getClobber(LI);
+        if (auto *QuerySI = dyn_cast<StoreInst>(QueryInst))
+          if (!QuerySI->isSimple())
+            return MemDepResult::getClobber(LI);
+      }
+
+      // FIXME: this is overly conservative.
+      // While volatile access cannot be eliminated, they do not have to clobber
+      // non-aliasing locations, as normal accesses can for example be reordered
+      // with volatile accesses.
+      if (LI->isVolatile())
         return MemDepResult::getClobber(LI);
 
       AliasAnalysis::Location LoadLoc = AA->getLocation(LI);
@@ -469,8 +490,26 @@ getPointerDependencyFrom(const AliasAnalysis::Location &MemLoc, bool isLoad,
 
     if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
       // Atomic stores have complications involved.
+      // A monotonic store is OK if the query inst is itself not atomic.
       // FIXME: This is overly conservative.
-      if (!SI->isUnordered())
+      if (!SI->isUnordered()) {
+        if (!QueryInst)
+          return MemDepResult::getClobber(SI);
+        if (SI->getOrdering() != Monotonic)
+          return MemDepResult::getClobber(SI);
+        if (auto *QueryLI = dyn_cast<LoadInst>(QueryInst))
+          if (!QueryLI->isSimple())
+            return MemDepResult::getClobber(SI);
+        if (auto *QuerySI = dyn_cast<StoreInst>(QueryInst))
+          if (!QuerySI->isSimple())
+            return MemDepResult::getClobber(SI);
+      }
+
+      // FIXME: this is overly conservative.
+      // While volatile access cannot be eliminated, they do not have to clobber
+      // non-aliasing locations, as normal accesses can for example be reordered
+      // with volatile accesses.
+      if (SI->isVolatile())
         return MemDepResult::getClobber(SI);
 
       // If alias analysis can tell that this store is guaranteed to not modify