fix the opt's crash bug caused by "-early-cse-memssa -early-cse-memssa"

[cszide]

Summary

The optimization sequence "-early-cse-memssa -early-cse-memssa" will cause a crash bug for opt tool with any input. This is because that the LegacyPassManager can not correctly process the dependency of the second "-early-cse-memssa".

The "-early-cse-memssa" pass requires analysis pass "Memory SSA" and will preserves it. However, the "-early-cse-memssa" pass can not preserve pass "Function Alias Analysis Results", which is required by pass "Memory SSA" and it will be removed after the first "-early-cse-memssa". Thus, when adding the second "-early-cse-memssa", the LegacyPassManager find that the analysis pass "Memory SSA" is already existed, which causes that the required pass "Function Alias Analysis Results" can not be satisfied for the second "-early-cse-memssa".

PS: This bug has been verified using llvm 6/7 and the truck version.

[cszide]

The bug has been fixed by other patch.

lib/IR/LegacyPassManager.cpp

           // passes are run on the fly.
           delete AnalysisPass;
       }
+      else{
+        AnalysisUsage *TrAnUsage = findAnalysisUsage(AnalysisPass);
+        const AnalysisUsage::VectorType &TrIDs = TrAnUsage->getRequiredTransitiveSet();
+        for (AnalysisID ID : TrIDs) {
+          Pass *TrAP = findAnalysisPass(ID);
+          if(!TrAP){
+            const PassInfo *PI = findAnalysisPassInfo(ID);
+
+            if (!PI) {
+              // Pass P is not in the global PassRegistry
+              dbgs() << "Pass '"  << P->getPassName() << "' is not initialized." << "\n";
+              dbgs() << "Verify if there is a pass dependency cycle." << "\n";
+              dbgs() << "Required Passes:" << "\n";
+              for (const AnalysisID ID2 : RequiredSet) {
+                if (ID == ID2)
+                  break;
+                Pass *AnalysisPass2 = findAnalysisPass(ID2);
+                if (AnalysisPass2) {
+                  dbgs() << "\t" << AnalysisPass2->getPassName() << "\n";
+                } else {
+                  dbgs() << "\t"   << "Error: Required pass not found! Possible causes:"  << "\n";
+                  dbgs() << "\t\t" << "- Pass misconfiguration (e.g.: missing macros)"    << "\n";
+                  dbgs() << "\t\t" << "- Corruption of the global PassRegistry"           << "\n";
+                }
+              }
+            }
+
+            assert(PI && "Expected required passes to be initialized");
+            AnalysisPass = PI->createPass();
+            if (P->getPotentialPassManagerType () ==
+              AnalysisPass->getPotentialPassManagerType())
+            // Schedule analysis pass that is managed by the same pass manager.
+            schedulePass(AnalysisPass);
+            else if (P->getPotentialPassManagerType () >
+                 AnalysisPass->getPotentialPassManagerType()) {
+              // Schedule analysis pass that is managed by a new manager.
+              schedulePass(AnalysisPass);
+              // Recheck analysis passes to ensure that required analyses that
+              // are already checked are still available.
+              checkAnalysis = true;
+            } else
+              // Do not schedule this analysis. Lower level analysis
+              // passes are run on the fly.
+              delete AnalysisPass;
+          }
+        }
+      }
     }
   }