The HoistAssumptions function would previously generate instructions

in-between phi nodes, thus breaking the basic block rule mandating to have *all*
phi nodes at the beginning of a block.
This led subsequent passes that iterate over instructions to find phi nodes to
incorrectly stop as soon as it found a non PHI node instruction, when in fact
there might still have been phi nodes afterwards.

Change-Id: I5fbb4491bab1437270f87a85b9ee5d595e1f9bab

Author: jsantillan2017

IGC/Compiler/CISACodeGen/UniformAssumptions.cpp

@@ -197,11 +197,20 @@ namespace IGC {
                         newAssumption->setOperand(0, src);
                         if (auto srcInst = dyn_cast<Instruction>(src))
                         {
-                            newAssumption->insertAfter(srcInst);
+                            if (isa<PHINode>(srcInst))
+                            {
+                                newAssumption->insertBefore(
+                                    srcInst->getParent()->getFirstNonPHI());
+                            }
+                            else
+                            {
+                                newAssumption->insertAfter(srcInst);
+                            }
                         }
                         else
                         {
-                            newAssumption->insertBefore(F.getEntryBlock().getFirstNonPHI());
+                            newAssumption->insertBefore(
+                                F.getEntryBlock().getFirstNonPHI());
                         }
                         check_further = true;
                     }