[LoopUnswitch] Check OptimizeForSize before traversing over all basic blocks in current loop

[• chenli]

Summary

This patch moves the check of OptimizeForSize before traversing over all basic blocks in current loop. If OptimizeForSize is set to true, no non-trivial unswitch is ever allowed. Therefore, the early exit will help reduce compilation time. This patch should be NFC.

[• chenli]

Initial patch was attached incorrectly by accident. Update the correct one.

[reames]

LGTM

[weimingz]

LGTM

lib/Transforms/Scalar/LoopUnswitch.cpp

if (!BranchesInfo.countLoop(
           AC))
     return false;
 
   // Try trivial unswitch first before loop over other basic blocks in the loop.
   if (TryTrivialLoopUnswitch(Changed)) {
     return true;
   }
 
+  // Do not do non-trivial unswitch while optimizing for size.
+  // FIXME: Use Function::optForSize().
+  if (OptimizeForSize ||
+      loopHeader->getParent()->hasFnAttribute(Attribute::OptimizeForSize))
+    return false;
+
   // Loop over all of the basic blocks in the loop.  If we find an interior
   // block that is branching on a loop-invariant condition, we can unswitch this
   // loop.
   for (Loop::block_iterator I = currentLoop->block_begin(),
          E = currentLoop->block_end(); I != E; ++I) {
     TerminatorInst *TI = (*I)->getTerminator();
     if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
       // If this isn't branching on an invariant condition, we can't unswitch
static BasicBlock *isTrivialLoopExitBlock(Loop *L, BasicBlock *BB) {
   return nullptr;
 }
 
 /// We have found that we can unswitch currentLoop when LoopCond == Val to
 /// simplify the loop.  If we decide that this is profitable,
 /// unswitch the loop, reprocess the pieces, then return true.
 bool LoopUnswitch::UnswitchIfProfitable(Value *LoopCond, Constant *Val,
                                         TerminatorInst *TI) {
-  Function *F = loopHeader->getParent();
-
   // Check to see if it would be profitable to unswitch current loop.
   if (!BranchesInfo.CostAllowsUnswitching()) {
     DEBUG(dbgs() << "NOT unswitching loop %"
                  << currentLoop->getHeader()->getName()
                  << " at non-trivial condition '" << *Val
                  << "' == " << *LoopCond << "\n"
                  << ". Cost too high.\n");
     return false;
   }
 
-  // Do not do non-trivial unswitch while optimizing for size.
-  // FIXME: Use Function::optForSize().
-  if (OptimizeForSize || F->hasFnAttribute(Attribute::OptimizeForSize))
-    return false;
-
   UnswitchNontrivialCondition(LoopCond, Val, currentLoop, TI);
   return true;
 }
 
 /// Recursively clone the specified loop and all of its children,
 /// mapping the blocks with the specified map.
 static Loop *CloneLoop(Loop *L, Loop *PL, ValueToValueMapTy &VM,
                        LoopInfo *LI, LPPassManager *LPM) {