PR9634: Don't unconditionally tell the AliasSetTracker that the PreheaderLoad

is equivalent to any other relevant value; it isn't true in general.
If it is equivalent, the LoopPromoter will tell the AST the equivalence.
Also, delete the PreheaderLoad if it is unused.

Chris, since you were the last one to make major changes here, can you check
that this is sane?

llvm-svn: 129049

1 files changed, 4 insertions, 21 deletions

diff --git a/llvm/lib/Transforms/Scalar/LICM.cpp b/llvm/lib/Transforms/Scalar/LICM.cpp
index 6cf1bd3deb5..93de9cf002e 100644
--- a/llvm/lib/Transforms/Scalar/LICM.cpp
+++ b/llvm/lib/Transforms/Scalar/LICM.cpp
@@ -743,30 +743,13 @@ void LICM::PromoteAliasSet(AliasSet &AS) {
                  Preheader->getTerminator());
   SSA.AddAvailableValue(Preheader, PreheaderLoad);
 
-  // Copy any value stored to or loaded from a must-alias of the pointer.
-  if (PreheaderLoad->getType()->isPointerTy()) {
-    Value *SomeValue;
-    if (LoadInst *LI = dyn_cast<LoadInst>(LoopUses[0]))
-      SomeValue = LI;
-    else
-      SomeValue = cast<StoreInst>(LoopUses[0])->getValueOperand();
-    
-    CurAST->copyValue(SomeValue, PreheaderLoad);
-  }
-
   // Rewrite all the loads in the loop and remember all the definitions from
   // stores in the loop.
   Promoter.run(LoopUses);
-  
-  // If the preheader load is itself a pointer, we need to tell alias analysis
-  // about the new pointer we created in the preheader block and about any PHI
-  // nodes that just got inserted.
-  if (PreheaderLoad->getType()->isPointerTy()) {
-    for (unsigned i = 0, e = NewPHIs.size(); i != e; ++i)
-      CurAST->copyValue(PreheaderLoad, NewPHIs[i]);
-  }
-  
-  // fwew, we're done!
+
+  // If the SSAUpdater didn't use the load in the preheader, just zap it now.
+  if (PreheaderLoad->use_empty())
+    PreheaderLoad->eraseFromParent();
 }