[DCE] Always get TargetLibraryInfo

[aeubanks]

Summary

I don't see any reason not to unconditionally retrieve TLI, it's fairly
cheap.

Fixes calls-errno.ll under NPM.

[aeubanks]

actually the legacy PM does the same thing, and also opt registers TLI analysis, will take another look

[aeubanks]

also change legacy pass

[aeubanks]

looks like opt registers its own TargetLibraryAnalysis but that doesn't count as running it, so getCachedResult returns null

llvm/lib/Transforms/Scalar/DCE.cpp

static bool eliminateDeadCode(Function &F, TargetLibraryInfo *TLI) {
   while (!WorkList.empty()) {
     Instruction *I = WorkList.pop_back_val();
     MadeChange |= DCEInstruction(I, WorkList, TLI);
   }
   return MadeChange;
 }
 
 PreservedAnalyses DCEPass::run(Function &F, FunctionAnalysisManager &AM) {
-  if (!eliminateDeadCode(F, AM.getCachedResult<TargetLibraryAnalysis>(F)))
+  if (!eliminateDeadCode(F, &AM.getResult<TargetLibraryAnalysis>(F)))
     return PreservedAnalyses::all();
 
   PreservedAnalyses PA;
   PA.preserveSet<CFGAnalyses>();
   return PA;
 }
 
 namespace {
 struct DCELegacyPass : public FunctionPass {
   static char ID; // Pass identification, replacement for typeid
   DCELegacyPass() : FunctionPass(ID) {
     initializeDCELegacyPassPass(*PassRegistry::getPassRegistry());
   }
 
   bool runOnFunction(Function &F) override {
     if (skipFunction(F))
       return false;
 
-    auto *TLIP = getAnalysisIfAvailable<TargetLibraryInfoWrapperPass>();
-    TargetLibraryInfo *TLI = TLIP ? &TLIP->getTLI(F) : nullptr;
+    TargetLibraryInfo *TLI =
+        &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(F);
 
     return eliminateDeadCode(F, TLI);
   }
 
   void getAnalysisUsage(AnalysisUsage &AU) const override {
+    AU.addRequired<TargetLibraryInfoWrapperPass>();
     AU.setPreservesCFG();
   }
 };
 }
 
 char DCELegacyPass::ID = 0;
 INITIALIZE_PASS(DCELegacyPass, "dce", "Dead Code Elimination", false, false)
 
 FunctionPass *llvm::createDeadCodeEliminationPass() {
   return new DCELegacyPass();
 }

llvm/test/Transforms/DCE/calls-errno.ll

 ; RUN: opt < %s -dce -S | FileCheck %s
+; RUN: opt < %s -passes=dce -S | FileCheck %s
 
 declare double @acos(double) nounwind
 declare double @asin(double) nounwind
 declare double @atan(double) nounwind
 declare double @atan2(double, double) nounwind
 declare double @ceil(double) nounwind
 declare double @cos(double) nounwind
 declare double @cosh(double) nounwind