[Utils] Avoid repeated hash lookups (NFC)

[kazutakahirata]

It's safe to use try_emplace instead of operator[] here because:

• PhiPredIVs is empty at the beginning of the loop, and

• The elements we are inserting into PhiPredIVs are unique.

[llvmbot]

@llvm/pr-subscribers-llvm-transforms

Author: Kazu Hirata (kazutakahirata)

Changes

It's safe to use try_emplace instead of operator[] here because:

• PhiPredIVs is empty at the beginning of the loop, and

• The elements we are inserting into PhiPredIVs are unique.

---

Full diff: https://github.com/llvm/llvm-project/pull/131267.diff

1 Files Affected:

• (modified) llvm/lib/Transforms/Utils/SimplifyCFG.cpp (+3-3)

diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index 833dc7331aecd..3a849bca36b2a 100644
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -7542,10 +7542,10 @@ bool SimplifyCFGOpt::simplifyDuplicateSwitchArms(SwitchInst *SI,
   // SwitchSuccWrapper.
   PhiPredIVs.reserve(Phis.size());
   for (PHINode *Phi : Phis) {
-    PhiPredIVs[Phi] =
-        SmallDenseMap<BasicBlock *, Value *, 8>(Phi->getNumIncomingValues());
+    auto &IVs =
+        PhiPredIVs.try_emplace(Phi, Phi->getNumIncomingValues()).first->second;
     for (auto &IV : Phi->incoming_values())
-      PhiPredIVs[Phi].insert({Phi->getIncomingBlock(IV), IV.get()});
+      IVs.insert({Phi->getIncomingBlock(IV), IV.get()});
   }
 
   // Build a set such that if the SwitchSuccWrapper exists in the set and