Extract FindAvailablePtrLoadStore out of FindAvailableLoadedValue. NFCI

trentxintong · trentxintong · commit aef0fcb19110 · 2017-03-19T15:27:52.000Z
Summary: Extract FindAvailablePtrLoadStore out of FindAvailableLoadedValue. Prepare for upcoming change which will do phi-translation for load on phi pointer in jump threading SimplifyPartiallyRedundantLoad. This is in preparation for https://reviews.llvm.org/D30543 Reviewers: efriedma, sanjoy, davide, dberlin Reviewed By: davide Subscribers: junbuml, davide, llvm-commits Differential Revision: https://reviews.llvm.org/D30524 llvm-svn: 298216
diff --git a/llvm/include/llvm/Analysis/Loads.h b/llvm/include/llvm/Analysis/Loads.h
@@ -88,6 +88,34 @@ Value *FindAvailableLoadedValue(LoadInst *Load,
                                 bool *IsLoadCSE = nullptr,
                                 unsigned *NumScanedInst = nullptr);
 
+/// Scan backwards to see if we have the value of the given pointer available
+/// locally within a small number of instructions.
+///
+/// You can use this function to scan across multiple blocks: after you call
+/// this function, if ScanFrom points at the beginning of the block, it's safe
+/// to continue scanning the predecessors.
+///
+/// \param Ptr The pointer we want the load and store to originate from.
+/// \param AccessTy The access type of the pointer.
+/// \param AtLeastAtomic Are we looking for at-least an atomic load/store ? In
+/// case it is false, we can return an atomic or non-atomic load or store. In
+/// case it is true, we need to return an atomic load or store.
+/// \param ScanBB The basic block to scan.
+/// \param [in,out] ScanFrom The location to start scanning from. When this
+/// function returns, it points at the last instruction scanned.
+/// \param MaxInstsToScan The maximum number of instructions to scan. If this
+/// is zero, the whole block will be scanned.
+/// \param AA Optional pointer to alias analysis, to make the scan more
+/// precise.
+/// \param [out] IsLoad Whether the returned value is a load from the same
+/// location in memory, as opposed to the value operand of a store.
+///
+/// \returns The found value, or nullptr if no value is found.
+Value *FindAvailablePtrLoadStore(Value *Ptr, Type *AccessTy, bool AtLeastAtomic,
+                                 BasicBlock *ScanBB,
+                                 BasicBlock::iterator &ScanFrom,
+                                 unsigned MaxInstsToScan, AliasAnalysis *AA,
+                                 bool *IsLoad, unsigned *NumScanedInst);
 }
 
 #endif
diff --git a/llvm/lib/Analysis/Loads.cpp b/llvm/lib/Analysis/Loads.cpp
@@ -312,22 +312,26 @@ Value *llvm::FindAvailableLoadedValue(LoadInst *Load,
                                       BasicBlock *ScanBB,
                                       BasicBlock::iterator &ScanFrom,
                                       unsigned MaxInstsToScan,
-                                      AliasAnalysis *AA, bool *IsLoadCSE,
+                                      AliasAnalysis *AA, bool *IsLoad,
                                       unsigned *NumScanedInst) {
-  if (MaxInstsToScan == 0)
-    MaxInstsToScan = ~0U;
-
-  Value *Ptr = Load->getPointerOperand();
-  Type *AccessTy = Load->getType();
-
-  // We can never remove a volatile load
-  if (Load->isVolatile())
-    return nullptr;
-
-  // Anything stronger than unordered is currently unimplemented.
+  // Don't CSE load that is volatile or anything stronger than unordered.
   if (!Load->isUnordered())
     return nullptr;
 
+  return FindAvailablePtrLoadStore(
+      Load->getPointerOperand(), Load->getType(), Load->isAtomic(), ScanBB,
+      ScanFrom, MaxInstsToScan, AA, IsLoad, NumScanedInst);
+}
+
+Value *llvm::FindAvailablePtrLoadStore(Value *Ptr, Type *AccessTy,
+                                       bool AtLeastAtomic, BasicBlock *ScanBB,
+                                       BasicBlock::iterator &ScanFrom,
+                                       unsigned MaxInstsToScan,
+                                       AliasAnalysis *AA, bool *IsLoadCSE,
+                                       unsigned *NumScanedInst) {
+  if (MaxInstsToScan == 0)
+    MaxInstsToScan = ~0U;
+
   const DataLayout &DL = ScanBB->getModule()->getDataLayout();
 
   // Try to get the store size for the type.
@@ -363,7 +367,7 @@ Value *llvm::FindAvailableLoadedValue(LoadInst *Load,
 
         // We can value forward from an atomic to a non-atomic, but not the
         // other way around.
-        if (LI->isAtomic() < Load->isAtomic())
+        if (LI->isAtomic() < AtLeastAtomic)
           return nullptr;
 
         if (IsLoadCSE)
@@ -382,7 +386,7 @@ Value *llvm::FindAvailableLoadedValue(LoadInst *Load,
 
         // We can value forward from an atomic to a non-atomic, but not the
         // other way around.
-        if (SI->isAtomic() < Load->isAtomic())
+        if (SI->isAtomic() < AtLeastAtomic)
           return nullptr;
 
         if (IsLoadCSE)
