From c6897706b7c3796ac24535c9ea1449c0411f8c7a Mon Sep 17 00:00:00 2001
From: Dan Gohman <gohman@apple.com>
Date: Thu, 7 Oct 2010 23:33:43 +0000
Subject: [PATCH] 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.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@116005 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Transforms/Scalar/LoopStrengthReduce.cpp | 27 ++++++++++++++------
 1 file changed, 19 insertions(+), 8 deletions(-)

diff --git a/lib/Transforms/Scalar/LoopStrengthReduce.cpp b/lib/Transforms/Scalar/LoopStrengthReduce.cpp
index 90af6c9ee5a..07477661f9a 100644
--- a/lib/Transforms/Scalar/LoopStrengthReduce.cpp
+++ b/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;