From cc4903e2ba9ae398a0afb9e442cb441ca1c60695 Mon Sep 17 00:00:00 2001
From: Daniel Jasper <djasper@google.com>
Date: Tue, 2 Jan 2018 14:38:52 +0000
Subject: Revert r321089: "[DAG] Elide overlapping store" (and subsequent fix
 in r321204)

Our internal testing has revealed has discovered bugs in PPC builds.
I have forward reproduction instructions to the original author (Nirav).

llvm-svn: 321649
---
 llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp | 42 +++++++++++++--------------
 1 file changed, 21 insertions(+), 21 deletions(-)

(limited to 'llvm/lib/CodeGen')

diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 5843f86a842..81bff4d7eef 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -13782,30 +13782,30 @@ SDValue DAGCombiner::visitSTORE(SDNode *N) {
     }
   }
 
-  // Deal with elidable overlapping chained stores.
-  if (StoreSDNode *ST1 = dyn_cast<StoreSDNode>(Chain))
-    if (OptLevel != CodeGenOpt::None && ST->isUnindexed() &&
-        ST1->isUnindexed() && !ST1->isVolatile() && ST1->hasOneUse() &&
-        !ST1->getBasePtr().isUndef() && !ST->isVolatile()) {
-      BaseIndexOffset STBasePtr = BaseIndexOffset::match(ST->getBasePtr(), DAG);
-      BaseIndexOffset ST1BasePtr =
-          BaseIndexOffset::match(ST1->getBasePtr(), DAG);
-      unsigned STBytes = ST->getMemoryVT().getStoreSize();
-      unsigned ST1Bytes = ST1->getMemoryVT().getStoreSize();
-      int64_t PtrDiff;
-      // If this is a store who's preceeding store to a subset of the same
-      // memory and no one other node is chained to that store we can
-      // effectively drop the store. Do not remove stores to undef as they may
-      // be used as data sinks.
-
-      if (((ST->getBasePtr() == ST1->getBasePtr()) &&
-           (ST->getValue() == ST1->getValue())) ||
-          (STBasePtr.equalBaseIndex(ST1BasePtr, DAG, PtrDiff) &&
-           (0 <= PtrDiff) && (PtrDiff + ST1Bytes <= STBytes))) {
+  if (StoreSDNode *ST1 = dyn_cast<StoreSDNode>(Chain)) {
+    if (ST->isUnindexed() && !ST->isVolatile() && ST1->isUnindexed() &&
+        !ST1->isVolatile() && ST1->getBasePtr() == Ptr &&
+        ST->getMemoryVT() == ST1->getMemoryVT()) {
+      // If this is a store followed by a store with the same value to the same
+      // location, then the store is dead/noop.
+      if (ST1->getValue() == Value) {
+        // The store is dead, remove it.
+        return Chain;
+      }
+
+      // If this is a store who's preceeding store to the same location
+      // and no one other node is chained to that store we can effectively
+      // drop the store. Do not remove stores to undef as they may be used as
+      // data sinks.
+      if (OptLevel != CodeGenOpt::None && ST1->hasOneUse() &&
+          !ST1->getBasePtr().isUndef()) {
+        // ST1 is fully overwritten and can be elided. Combine with it's chain
+        // value.
         CombineTo(ST1, ST1->getChain());
-        return SDValue(N, 0);
+        return SDValue();
       }
     }
+  }
 
   // If this is an FP_ROUND or TRUNC followed by a store, fold this into a
   // truncating store.  We can do this even if this is already a truncstore.
-- 
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