Fix LSR to keep the RegUseTracker up to date when combining users.

This doesn't usually matter, because the other heuristics usually
succeed regardless, but it's good to keep the register use
bookkeeping consistent.

llvm-svn: 116005

llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp

@@ -113,7 +113,7 @@ class RegUseTracker {
 public:
   void CountRegister(const SCEV *Reg, size_t LUIdx);
   void DropRegister(const SCEV *Reg, size_t LUIdx);
-  void DropUse(size_t LUIdx);
+  void SwapAndDropUse(size_t LUIdx, size_t LastLUIdx);
 
   bool isRegUsedByUsesOtherThan(const SCEV *Reg, size_t LUIdx) const;
 
@@ -152,11 +152,19 @@ RegUseTracker::DropRegister(const SCEV *Reg, size_t LUIdx) {
 }
 
 void
-RegUseTracker::DropUse(size_t LUIdx) {
-  // Remove the use index from every register's use list.
+RegUseTracker::SwapAndDropUse(size_t LUIdx, size_t LastLUIdx) {
+  assert(LUIdx <= LastLUIdx);
+
+  // Update RegUses. The data structure is not optimized for this purpose;
+  // we must iterate through it and update each of the bit vectors.
   for (RegUsesTy::iterator I = RegUsesMap.begin(), E = RegUsesMap.end();
-       I != E; ++I)
-    I->second.UsedByIndices.reset(LUIdx);
+       I != E; ++I) {
+    SmallBitVector &UsedByIndices = I->second.UsedByIndices;
+    if (LUIdx < UsedByIndices.size())
+      UsedByIndices[LUIdx] =
+        LastLUIdx < UsedByIndices.size() ? UsedByIndices[LastLUIdx] : 0;
+    UsedByIndices.resize(std::min(UsedByIndices.size(), LastLUIdx));
+  }
 }
 
 bool
@@ -1339,7 +1347,7 @@ class LSRInstance {
                                     LSRUse::KindType Kind,
                                     const Type *AccessTy);
 
-  void DeleteUse(LSRUse &LU);
+  void DeleteUse(LSRUse &LU, size_t LUIdx);
 
   LSRUse *FindUseWithSimilarFormula(const Formula &F, const LSRUse &OrigLU);
 
@@ -1923,10 +1931,13 @@ LSRInstance::getUse(const SCEV *&Expr,
 }
 
 /// DeleteUse - Delete the given use from the Uses list.
-void LSRInstance::DeleteUse(LSRUse &LU) {
+void LSRInstance::DeleteUse(LSRUse &LU, size_t LUIdx) {
   if (&LU != &Uses.back())
     std::swap(LU, Uses.back());
   Uses.pop_back();
+
+  // Update RegUses.
+  RegUses.SwapAndDropUse(LUIdx, Uses.size());
 }
 
 /// FindUseWithFormula - Look for a use distinct from OrigLU which is has
@@ -3032,7 +3043,7 @@ void LSRInstance::NarrowSearchSpaceByCollapsingUnrolledCode() {
               }
 
               // Delete the old use.
-              DeleteUse(LU);
+              DeleteUse(LU, LUIdx);
               --LUIdx;
               --NumUses;
               break;