Merging r167912: into the 3.2 release branch.

Handle DAG CSE adding new uses during ReplaceAllUsesWith. Fixes PR14333.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/branches/release_32@168596 91177308-0d34-0410-b5e6-96231b3b80d8

Author: 32bitmicro

lib/CodeGen/SelectionDAG/DAGCombiner.cpp

@@ -7728,7 +7728,18 @@ bool DAGCombiner::MergeConsecutiveStores(StoreSDNode* St) {
       if (StoreNodes[i].MemNode == EarliestOp)
         continue;
       StoreSDNode *St = cast<StoreSDNode>(StoreNodes[i].MemNode);
-      DAG.ReplaceAllUsesOfValueWith(SDValue(St, 0), St->getChain());
+      // ReplaceAllUsesWith will replace all uses that existed when it was
+      // called, but graph optimizations may cause new ones to appear. For
+      // example, the case in pr14333 looks like
+      //
+      //  St's chain -> St -> another store -> X
+      //
+      // And the only difference from St to the other store is the chain.
+      // When we change it's chain to be St's chain they become identical,
+      // get CSEed and the net result is that X is now a use of St.
+      // Since we know that St is redundant, just iterate.
+      while (!St->use_empty())
+        DAG.ReplaceAllUsesWith(SDValue(St, 0), St->getChain());
       removeFromWorkList(St);
       DAG.DeleteNode(St);
     }

test/CodeGen/X86/pr14333.ll

@@ -0,0 +1,12 @@
+; RUN: llc -mtriple=x86_64-unknown-unknown < %s
+%foo = type { i64, i64 }
+define void @bar(%foo* %zed) {
+  %tmp = getelementptr inbounds %foo* %zed, i64 0, i32 0
+  store i64 0, i64* %tmp, align 8
+  %tmp2 = getelementptr inbounds %foo* %zed, i64 0, i32 1
+  store i64 0, i64* %tmp2, align 8
+  %tmp3 = bitcast %foo* %zed to i8*
+  call void @llvm.memset.p0i8.i64(i8* %tmp3, i8 0, i64 16, i32 8, i1 false)
+  ret void
+}
+declare void @llvm.memset.p0i8.i64(i8* nocapture, i8, i64, i32, i1) nounwind