Revert r56315. When the instruction to speculate is a load, this

code can incorrectly move the load across a store. This never
happens in practice today, but only because the current
heuristics accidentally preclude it.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@147623 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Transforms/Utils/SimplifyCFG.cpp

@@ -1063,32 +1063,8 @@ static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *BB1) {
       return false;
   }
 
-  // If we get here, we can hoist the instruction. Try to place it
-  // before the icmp instruction preceding the conditional branch.
-  BasicBlock::iterator InsertPos = BI;
-  if (InsertPos != BIParent->begin())
-    --InsertPos;
-  // Skip debug info between condition and branch.
-  while (InsertPos != BIParent->begin() && isa<DbgInfoIntrinsic>(InsertPos))
-    --InsertPos;
-  if (InsertPos == BrCond && !isa<PHINode>(BrCond)) {
-    SmallPtrSet<Instruction *, 4> BB1Insns;
-    for(BasicBlock::iterator BB1I = BB1->begin(), BB1E = BB1->end(); 
-        BB1I != BB1E; ++BB1I) 
-      BB1Insns.insert(BB1I);
-    for(Value::use_iterator UI = BrCond->use_begin(), UE = BrCond->use_end();
-        UI != UE; ++UI) {
-      Instruction *Use = cast<Instruction>(*UI);
-      if (!BB1Insns.count(Use)) continue;
-      
-      // If BrCond uses the instruction that place it just before
-      // branch instruction.
-      InsertPos = BI;
-      break;
-    }
-  } else
-    InsertPos = BI;
-  BIParent->getInstList().splice(InsertPos, BB1->getInstList(), HInst);
+  // If we get here, we can hoist the instruction.
+  BIParent->getInstList().splice(BI, BB1->getInstList(), HInst);
 
   // Create a select whose true value is the speculatively executed value and
   // false value is the previously determined FalseV.

test/Transforms/SimplifyCFG/SpeculativeExec.ll

@@ -13,8 +13,8 @@ bb1:            ; preds = %entry
 	%tmp2 = icmp sgt i32 %c, 1
 	br i1 %tmp2, label %bb2, label %bb3
 ; CHECK: bb1:
-; CHECK-NEXT: add i32 %a, 1
 ; CHECK-NEXT: icmp sgt i32 %c, 1
+; CHECK-NEXT: add i32 %a, 1
 ; CHECK-NEXT: select i1 %tmp2, i32 %tmp3, i32 %a
 ; CHECK-NEXT: br label %bb3