[RewriteStatepoints] Do not instert Store before Phi

[yrouban]

Summary

When Store instructions are emitted they must not be followed by phi nodes.

[dneilson]

Please add a test case that demonstrates the patch in action (and would prevent regressions).

[yrouban]

lib/Transforms/Scalar/RewriteStatepointsForGC.cpp

1869

Use getFirstInsertionPt() instead of getFirstNonPHI()

lib/Transforms/Scalar/RewriteStatepointsForGC.cpp

if (Instruction *Inst = dyn_cast<Instruction>(Def)) {
         // InvokeInst is a TerminatorInst so the store need to be inserted
         // into its normal destination block.
         BasicBlock *NormalDest = Invoke->getNormalDest();
         Store->insertBefore(NormalDest->getFirstNonPHI());
       } else {
         assert(!Inst->isTerminator() &&
                "The only TerminatorInst that can produce a value is "
                "InvokeInst which is handled above.");
+        if (isa<PHINode>(Inst)) {
+          Store->insertBefore(Inst->getParent()->getFirstNonPHI());
+        } else {
           Store->insertAfter(Inst);
         }
+      }
     } else {
       assert(isa<Argument>(Def));
       Store->insertAfter(cast<Instruction>(Alloca));
     }
+    assert(!isa<PHINode>(Store->getNextNode()) &&
+           "must not insert in front of phi");
   }
 
   assert(PromotableAllocas.size() == Live.size() + NumRematerializedValues &&
          "we must have the same allocas with lives");
   if (!PromotableAllocas.empty()) {
     // Apply mem2reg to promote alloca to SSA
     PromoteMemToReg(PromotableAllocas, DT);
   }