[LoopUnswitch] Add an else clause to IsTrivialUnswitchCondition() when checking HeaderTerm instruction type

[• chenli]

Summary

This is a trivial code change with no functionality effect.

When LoopUnswitch determines trivial unswitch condition, it checks whether the loop header's terminator instruction is a branch instruction or switch instruction since trivial unswitch condition can only apply to these two instruction types. The current code does not fail the check directly on other instruction types, but check the nullness of LoopExitBB variable instead. The added else clause makes the check fail immediately on other instruction types and makes the code more obvious.

[reames]

LGTM.

lib/Transforms/Scalar/LoopUnswitch.cpp

644

The comment doesn't seem to add much value. Possibly remove?

No need for curly braces.

[• chenli]

Revise wrt Philip's comments.

lib/Transforms/Scalar/LoopUnswitch.cpp

for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end();
         // trivial vals are looks trivial too.
         if (BranchesInfo.isUnswitched(SI, CaseVal))
           continue;
         LoopExitBB = LoopExitCandidate;
         if (Val) *Val = CaseVal;
         break;
       }
     }
+  } else {
+    // TrivialUnswitchCondition can only apply to BranchInst or SwitchInst.
+    // Anything else should return false immediately.
+    return false;
   }
 
   // If we didn't find a single unique LoopExit block, or if the loop exit block
   // contains phi nodes, this isn't trivial.
   if (!LoopExitBB || isa<PHINode>(LoopExitBB->begin()))
     return false;   // Can't handle this.
 
   if (LoopExit) *LoopExit = LoopExitBB;