[NFC][CodeGen] Modify the type element of TailCalls to simplify the dupRetToEnableTailCallOpts()

[ZhangKang]

Summary

Now, I am trying to improve the function dupRetToEnableTailCallOpts() to do more generate optimization not only for tail call.

When I do this work, I find the old code can be simplified to define the element type of TailCalls as BasicBlock not CallInst.

[jsji]

LGTM.

llvm/lib/CodeGen/CodeGenPrepare.cpp

2061

Can this be a range based for?

[ZhangKang]

Use the for range loop.

[ZhangKang]

llvm/lib/CodeGen/CodeGenPrepare.cpp

2061

Done.

llvm/lib/CodeGen/CodeGenPrepare.cpp

   /// Only dup the ReturnInst if the CallInst is likely to be emitted as a tail
   /// call.
   const Function *F = BB->getParent();
-  SmallVector<CallInst*, 4> TailCalls;
+  SmallVector<BasicBlock*, 4> TailCallBB;
   if (PN) {
     for (unsigned I = 0, E = PN->getNumIncomingValues(); I != E; ++I) {
       // Look through bitcasts.
       Value *IncomingVal = PN->getIncomingValue(I)->stripPointerCasts();
       CallInst *CI = dyn_cast<CallInst>(IncomingVal);
+      BasicBlock *PredBB = PN->getIncomingBlock(I);
       // Make sure the phi value is indeed produced by the tail call.
-      if (CI && CI->hasOneUse() && CI->getParent() == PN->getIncomingBlock(I) &&
+      if (CI && CI->hasOneUse() && CI->getParent() == PredBB &&
           TLI->mayBeEmittedAsTailCall(CI) &&
           attributesPermitTailCall(F, CI, RetI, *TLI))
-        TailCalls.push_back(CI);
+        TailCallBB.push_back(PredBB);
     }
   } else {
     SmallPtrSet<BasicBlock*, 4> VisitedBBs;

       CallInst *CI = dyn_cast<CallInst>(&*RI);
       if (CI && CI->use_empty() && TLI->mayBeEmittedAsTailCall(CI) &&
           attributesPermitTailCall(F, CI, RetI, *TLI))
-        TailCalls.push_back(CI);
+        TailCallBB.push_back(*PI);
     }
   }
 
   bool Changed = false;
-  for (unsigned i = 0, e = TailCalls.size(); i != e; ++i) {
-    CallInst *CI = TailCalls[i];
-    CallSite CS(CI);
-
+  for (unsigned i = 0, e = TailCallBB.size(); i != e; ++i) {
     // Make sure the call instruction is followed by an unconditional branch to
     // the return block.
-    BasicBlock *CallBB = CI->getParent();
-    BranchInst *BI = dyn_cast<BranchInst>(CallBB->getTerminator());
+    BranchInst *BI = dyn_cast<BranchInst>(TailCallBB[i]->getTerminator());
     if (!BI || !BI->isUnconditional() || BI->getSuccessor(0) != BB)
       continue;
 
-    // Duplicate the return into CallBB.
-    (void)FoldReturnIntoUncondBranch(RetI, BB, CallBB);
+    // Duplicate the return into TailCallBB.
+    (void)FoldReturnIntoUncondBranch(RetI, BB, TailCallBB[i]);
     ModifiedDT = Changed = true;
     ++NumRetsDup;
   }