Avoid recomputing the unique exit blocks and their insert points when doing

multiple scalar promotions on a single loop. This also has the effect of
preserving the order of stores sunk out of loops, which is aesthetically
pleasing, and it happens to fix the testcase in PR13542, though it doesn't
fix the underlying problem.

llvm-svn: 161459

1 files changed, 26 insertions, 11 deletions

diff --git a/llvm/lib/Transforms/Scalar/LICM.cpp b/llvm/lib/Transforms/Scalar/LICM.cpp
index 582948ea14b..0192e928fe8 100644
--- a/llvm/lib/Transforms/Scalar/LICM.cpp
+++ b/llvm/lib/Transforms/Scalar/LICM.cpp
@@ -175,7 +175,9 @@ namespace {
     bool canSinkOrHoistInst(Instruction &I);
     bool isNotUsedInLoop(Instruction &I);
 
-    void PromoteAliasSet(AliasSet &AS);
+    void PromoteAliasSet(AliasSet &AS,
+                         SmallVectorImpl<BasicBlock*> &ExitBlocks,
+                         SmallVectorImpl<Instruction*> &InsertPts);
   };
 }
 
@@ -256,10 +258,13 @@ bool LICM::runOnLoop(Loop *L, LPPassManager &LPM) {
   // Now that all loop invariants have been removed from the loop, promote any
   // memory references to scalars that we can.
   if (!DisablePromotion && Preheader && L->hasDedicatedExits()) {
+    SmallVector<BasicBlock *, 8> ExitBlocks;
+    SmallVector<Instruction *, 8> InsertPts;
+
     // Loop over all of the alias sets in the tracker object.
     for (AliasSetTracker::iterator I = CurAST->begin(), E = CurAST->end();
          I != E; ++I)
-      PromoteAliasSet(*I);
+      PromoteAliasSet(*I, ExitBlocks, InsertPts);
   }
 
   // Clear out loops state information for the next iteration
@@ -631,6 +636,7 @@ namespace {
     Value *SomePtr;  // Designated pointer to store to.
     SmallPtrSet<Value*, 4> &PointerMustAliases;
     SmallVectorImpl<BasicBlock*> &LoopExitBlocks;
+    SmallVectorImpl<Instruction*> &LoopInsertPts;
     AliasSetTracker &AST;
     DebugLoc DL;
     int Alignment;
@@ -638,11 +644,12 @@ namespace {
     LoopPromoter(Value *SP,
                  const SmallVectorImpl<Instruction*> &Insts, SSAUpdater &S,
                  SmallPtrSet<Value*, 4> &PMA,
-                 SmallVectorImpl<BasicBlock*> &LEB, AliasSetTracker &ast,
-                 DebugLoc dl, int alignment)
+                 SmallVectorImpl<BasicBlock*> &LEB,
+                 SmallVectorImpl<Instruction*> &LIP,
+                 AliasSetTracker &ast, DebugLoc dl, int alignment)
       : LoadAndStorePromoter(Insts, S), SomePtr(SP),
-        PointerMustAliases(PMA), LoopExitBlocks(LEB), AST(ast), DL(dl),
-        Alignment(alignment) {}
+        PointerMustAliases(PMA), LoopExitBlocks(LEB), LoopInsertPts(LIP),
+        AST(ast), DL(dl), Alignment(alignment) {}
 
     virtual bool isInstInList(Instruction *I,
                               const SmallVectorImpl<Instruction*> &) const {
@@ -662,7 +669,7 @@ namespace {
       for (unsigned i = 0, e = LoopExitBlocks.size(); i != e; ++i) {
         BasicBlock *ExitBlock = LoopExitBlocks[i];
         Value *LiveInValue = SSA.GetValueInMiddleOfBlock(ExitBlock);
-        Instruction *InsertPos = ExitBlock->getFirstInsertionPt();
+        Instruction *InsertPos = LoopInsertPts[i];
         StoreInst *NewSI = new StoreInst(LiveInValue, SomePtr, InsertPos);
         NewSI->setAlignment(Alignment);
         NewSI->setDebugLoc(DL);
@@ -684,7 +691,9 @@ namespace {
 /// looping over the stores in the loop, looking for stores to Must pointers
 /// which are loop invariant.
 ///
-void LICM::PromoteAliasSet(AliasSet &AS) {
+void LICM::PromoteAliasSet(AliasSet &AS,
+                           SmallVectorImpl<BasicBlock*> &ExitBlocks,
+                           SmallVectorImpl<Instruction*> &InsertPts) {
   // We can promote this alias set if it has a store, if it is a "Must" alias
   // set, if the pointer is loop invariant, and if we are not eliminating any
   // volatile loads or stores.
@@ -794,14 +803,20 @@ void LICM::PromoteAliasSet(AliasSet &AS) {
   // location is better than none.
   DebugLoc DL = LoopUses[0]->getDebugLoc();
 
-  SmallVector<BasicBlock*, 8> ExitBlocks;
-  CurLoop->getUniqueExitBlocks(ExitBlocks);
+  // Figure out the loop exits and their insertion points, if this is the
+  // first promotion.
+  if (ExitBlocks.empty()) {
+    CurLoop->getUniqueExitBlocks(ExitBlocks);
+    InsertPts.resize(ExitBlocks.size());
+    for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i)
+      InsertPts[i] = ExitBlocks[i]->getFirstInsertionPt();
+  }
 
   // We use the SSAUpdater interface to insert phi nodes as required.
   SmallVector<PHINode*, 16> NewPHIs;
   SSAUpdater SSA(&NewPHIs);
   LoopPromoter Promoter(SomePtr, LoopUses, SSA, PointerMustAliases, ExitBlocks,
-                        *CurAST, DL, Alignment);
+                        InsertPts, *CurAST, DL, Alignment);
 
   // Set up the preheader to have a definition of the value.  It is the live-out
   // value from the preheader that uses in the loop will use.